CARBURATOR CENTRAL

Wideband Tuning for Carbureted Drag Racing

11-sec. Camaro on the Fast Track to a Perfect Tune. (By Stanford Curry)

This LogWorks chart shows a basic quarter-mile pass. As you read the chart from left-to-right, the black line represents engine RPM, showing four major peaks at 6900 RPM (for gears 1 – 4), followed by a drop into the next gear. The torque you feel in the car is shown in the orange Acceleration (g) line , which is strongest in first gear and trails off in subsequent gears. The Air/Fuel Mixture is the magenta line, and it should ideally hover between 12.5:1 to 13.5:1 in each gear. Also note the blue Vacuum line , showing when the driver's foot is to the floor (low vacuum) or when the driver lifts, as he did coming off the line in first gear to reduce wheelspin (where the orange Acceleration line dropped and black RPM line spiked). Each line has its scale represented in the left column

1. Recording & Displaying Live Data

2. Downloading & Viewing Recorded Data

3. Idle Tuning

4. Power Valve Tuning

5. Accelerator Pump Cam & Squirter Nozzle Tuning

6. Main Jet Tuning

7. Cruise Tuning

Carburetors are great for wide-open-throttle (WOT) applications like drag racing, thanks to their comparatively low cost and ease-of-setup. Assuming you have the right size of carburetor for your application and that your engine's in good working order (no fuel leaks, no ignition glitches, no parts rattling around in the oil pan), it's easy to get up and running and tap the potential of Innovate's tuning solutions. With an hour or two wrenching and running a few wires, you can capture data that allows you to track your air/fuel ratio, engine RPM, acceleration gs and vacuum (load) as your car travels down the strip. (Installation tips) The data you capture will help you spot top-end lean-out conditions, highlight traction issues and fine-tune part-throttle / cruise conditions where you can reduce fuel consumption. This overview provides examples of each as we discuss tuning carburetor components including main jets, power valve, accelerator pump and air bleeds (idle and high-speed

1. Recording & Displaying Live Data: Now that you've installed and configured the LM-1 and LMA-3, it's time to take your car for a drive, capture some data, interpret the results and make some tweaks where necessary. Like the install guide says, hit the LM-1's "Record" button once to start recording ("R" will flash on the LM-1's display) and once again to stop recording – this builds what is referred to as a "Session" in the LM-1. You can record multiple sessions and up to 44 minutes of total driving time before you have to download the data to your laptop and clear the LM-1's memory. If you still have the laptop attached to the LM-1, you can also maximize the LogWorks Monitor display and see your car's Air/Fuel, RPM, Vacuum and Acceleration while the car's running – handy if you're tuning the idle in the garage or riding along in the passenger seat while someone else drives your car (on the dyno or on the street).

2. Downloading & Viewing Recorded Data: Innovate makes it easy to pull recorded data down from the LM-1 to your laptop. With your laptop connected to the LM-1, open up the LogWorks Monitor software and click on the "File" drop-down menu and highlight "Download LM-1 Log" to load your recorded data to your laptop. Once the download completes, you'll see a new window appear with a graphical representation of your session – similar to the following picture. You can toggle between multiple sessions by clicking on the "Session" drop-down menu.

It's a good habit to immediately save this newly downloaded data onto your laptop before you clear out the LM-1's memory storage of its sessions. First, click on "File" in your newly created LogWorks graph window and then click on "Save As." Type a filename that includes something meaningful to you about the session (e.g., "80p88s.log" can denote 80 size primaries, 88 size secondaries). This filename needs to make sense to you when you revisit the information 2 – 3 months later in the racing season. Next, clear out the LM-1's memory by going back to the LogWorks Monitor and clicking "File" and then "Reset LM-1 Log."

The example below shows a basic chassis dyno pull from 3000 RPM to 7000 RPM (black line) with the pink Air/Fuel Ratio line indicating a slight lean-out condition after 5500 RPM. Spikes like these may point to a fuel delivery problem, so check your fuel bowl levels. Otherwise, the lean-out can be addressed by changing to a size or two larger on the main jets for both the primaries and secondaries. The blue line is Vacuum , showing that the driver's foot is to the floor all the way through the dyno pull. You can also add a note to the session by clicking on the little yellow note icon, just below the drop-down "Channels" menu and dragging it down to the Timeline area where you wish to append the information. The note information you add to that box will be displayed when you "mouse over" it with your cursor later.

As you can see in the following diagram, richening the jets two full numbers in the primary and secondary sides richened the mixture and reduced the high RPM lean-out as noted by the flatter pink Air/Fuel Ratio line through the pull.

We tuned for a mid-13 Air/Fuel Ratio here as a baseline. Even with the dyno pulls showing a flat Air/Fuel Ratio in the 13:1 range, a run down the track is the next logical step to test your baseline tuning. The conditions are usually different between dyno and track, providing the opportunity to further refine the jetting of the primary & secondary main circuits. Dyno vs. track conditions can vary in elevation, temperature, headwind, etc. You may also find the track passes sometimes highlight a lean-out condition caused by fuel bowl starvation – too small of a fuel line, too low of a fuel bowl level, not enough fuel pump volume, etc. As the log from a track run illustrates, the jetting was initially too lean in third and fourth gear, but richened with RPMs which at least rules out fuel delivery issues. Therefore, the next objective is to jet the carb in wide-open-throttle conditions for 13 – 13.5:1 Air/Fuel in third and fourth gear.

The preceding graphic shows that the car is running too lean in third and fourth gear ( Air/Fuel in the 14:1 range) with 80 size jets in the primaries (plus a power valve) and 88s in the secondaries. Standard practice recommends changing up or down 2 jet sizes front & rear at a time, which would have put us just about perfect if we had a set of 82s and 90s with us. We only had 83s and 92s at the time of this test which richened the Air/Fuel Ratio just a little too far – low 13s and high 12s as shown in the following diagram. What's important to note here is the sensitivity of Innovate's O2 readings. You can easily see that the Air/Fuel Ratio dropped from dangerously lean 14.5:1 to safely rich 12.5 – 13:1 through richening the main jets by a factor of 3.5 jet sizes (up 3 in the primaries, up 4 in the secondaries).

Innovate's point and click interface also makes it easy to stretch the timeline (click the magnifying glass and then click on the timeline across the bottom of the chart). You can also add the rectangular data boxes you see in the picture by clicking on the gauge icon and then clicking anywhere on the chart.

Innovate also provides you a facility to look at your session data as an aggregate of all the sessions instead of looking at run-by-run views of each line graph. You can also easily combine all of your sessions (dyno pulls, drag strip runs or street driving) and look at them in a single table. As shown in the graphic below, simply click on the LogWorks "View" drop-down menu, and then click "View Chart" which will bring up a table.

When the Table view comes up, click on the "Table" drop-down menu and select "Table Setup" to choose which variables you want to place on the vertical and horizontal axes of the table. A commonly used approach is to select RPM as the Horizontal X axis and Vacuum (or MAP) as the Vertical Y axis, and select Air/Fuel Rati o to fill in the Chart Content. The table's tabs allow you to look at the data points' Average, Standard Deviation, Number of Data Points, Maximum and Minimum values.

You can also enable color-coding by clicking on "Colors" and selecting the color scheme of your preference. Cells in the table are then color coded based on their numerical value. The color scheme in the following diagram is the "Wobniar" ("Rainbow" spelled backwards) which intuitively uses blue for the rich / cool side of the Air/Fuel Ratio spectrum and red as the lean / hot side.

You can also view the table's data as a three-dimensional graph by clicking on the table's drop-down menu choice of "View" and then click "View Table as a 3D Graph." The following diagram shows what the 3D graph looks like:

3. Idle Tuning: Get the car started and fully warmed up to operating temperature for at least 10 minutes – take a trip to the local store and back (this avoids tuning the car "cold" and subsequently running too rich when it is warmed up on cruise night). With your car in neutral or park, the laptop hooked into the LM-1 box and running the LogWorks Monitor software, you should see your Air/Fuel , RPM idle speed and Vacuum (MAP as PSI) on the laptop display, similar to what's shown in the following diagram.

Adjust your idle speed screw(s) for primaries (& secondaries if so equipped) to achieve your desired idle speed. Then adjust the idle mixture screws. Some carburetors only have two idle mixture screws for the primaries, while others offer a "4 corner idle system, using the primaries and secondaries. The goal is to achieve an Air/Fuel Ratio somewhere between 13:1 and 14.7:1 while maximizing your Vacuum reading. Looking at the Air/Fuel , RPM and Vacuum , you will find that barely moving your carb's idle mixture screws – maybe 1/16 th of a turn – can change the Air/Fuel Ratio over half of a point without any change in your perceived idle speed. This is just one area where Innovate's wideband really shines – sensitivity.

If the idle mixture screws don't have enough impact on the Air/Fuel Ratio or Vacuum , you can try incrementally changing the carb's idle feed restrictors and idle air bleeds (if the carb is so equipped). If the car idles with the idle mixture screws closed or nearly closed (less than a half turn from full clockwise / bottomed out), you can lean out the idle by substituting a smaller idle feed restrictor for the one currently in it, or you can try using a larger idle air bleed. If the car requires turning the mixture screws out from fully closed / bottomed, an abnormally large number of turns (4 turns out from fully closed), you can try richening the idle circuit by installing either a larger diameter idle feed restrictor or a smaller idle air bleed.

For cars with automatic transmissions and no "idle-compensation" solenoid triggered by the trans or A/C, you may face a tradeoff of idle quality when the transmission is in Park compared to when it's in Drive. Once you set the idle for Drive (optionally with the air conditioner running and lights on as your "highest load" worst case), you may wind up with a little lower Air/Fuel Ratio in Drive or higher idle speed in Park than you might otherwise prefer. Chock the drive wheels, set your emergency brake AND have a friend hold their foot on the brakes while keeping the engine running and transmission in Drive for this exercise. Try to achieve an acceptable idle speed while maximizing Vacuum and getting Air/Fuel Ratio between 12.5:1 and 14:1.

4. Power Valve Tuning: Once you have the idle speed and mixture set, take note of the Vacuum reading using your LM-1 and LogWorks software. If you have a carb that uses a "power valve" to enrich the mixture under load conditions for the primaries or secondaries, your should try using power valve with an opening level 2 – 3 inches below the idle vacuum (in Drive for automatics or Neutral for manuals). This gap prevents dumping too much fuel into the engine during either idle or cruise. You can see the power valve add fuel on the LogWorks chart by looking at the Vacuum reading (blue line) and the pink Air/Fuel Ratio reading. When the blue Vacuum line dips below the setting of the power valve (5.5 inches of vacuum, for example), the pink Air/Fuel Ratio will drop a point or two (from 14:1 down to 12:1) because the engine needs more fuel under that heavier load. In the same situation under load, if you were to lift back off of the throttle, this would raise the vacuum above 5.5 inches – and the Air/Fuel Ratio would rise back up from 12:1 to 14:1. At light loads above its stated rating (most are available from 2.5 inches up to 8.5) – the power valve is no longer active since the cruise and/or mains are providing enough fuel.

5. Accelerator Pump Cam & Squirter Nozzle Tuning: The accelerator pump system handles most of the "increase-in-load" fueling needs and can be seen on the LogWorks chart as a drop in Air/Fuel Ratio coinciding with a drop in Vacuum . If your mixture is too rich (e.g., 10:1) right after you floor it, try using a smaller-lift accelerator pump cam or retarding the pump cam by moving it to a different position on the throttle shaft. If you find that you have a lean spot a half second to a second after flooring the throttle, your accelerator pump nozzle may be too big. Try reducing the accelerator pump squirter nozzle size, which extends the duration of the accelerator pump's discharge – you should then see a smoothing or flattening a given Air/Fuel Ratio on charts after flooring the throttle. This effect is easily seen on charts for manual-transmission cars accelerating through the gears.

6. Main Jet Tuning: The main jets are the focus of most tuners working with a carb, and Innovate's wideband system makes this the simplest of all the tasks. Drive the car to a dyno shop, record a session (from 2500 or 3000 RPM through redline in third or fourth gear) and open LogWorks to view the RPM and Air/Fuel Ratio lines. The Air/Fuel Ratio may show a drop at the same time you floor it (the blue Vacuum line confirms this with a drop), but for now focus on the Air/Fuel Ratio and the shape of the line roughly 1.5 seconds after you floor it until redline. If the line is relatively flat and horizontal, hovering around 12.5:1 – 13.5:1, you're set. If it's above that range (too lean for wide open throttle), try going up two jet sizes (on a Holley or Demon carburetor – Edelbrocks, Carters and Quadrajets may be similar). If the Air/Fuel Ratio is below that range, it's richer than optimal unless you're either trying to combat detonation or are running a turbo/supercharger – so try leaning it out with a size or two smaller jet size. Once you're consistently pulling between 12.5:1 to 13.5:1 you should be ready for some tuning at the drag strip.

You should test your car both on the dyno and at the track, since the dyno doesn't offer the same variations in load, traction, wind resistance and temperature as the track. While at the track, pay attention to the Air/Fuel Ratio in each gear – the Acceleration / g reading (orange line) will come into play here as well. If your Air/Fuel Ratio is between 13.0:1 and 13.5:1 in all gears, you're in great shape. If it's too lean in first gear off the line but fine in the others, check the g reading – you may be pulling so hard off the line that you're uncovering jets. Possible cures include checking the float levels or getting main jet extensions for the secondaries. If your Air/Fuel Ratio is fine in first and second but starts to get too lean in third or fourth, you may be draining the fuel bowls faster than your fuel pump & lines can fill them. The diagram below shows a good bit of wheel spin modulation in first gear (RPM spike drop in orange g line) and flat Air/Fuel Ratio lines in gears 2-4 which will require slight richening from 14.4:1 down to 13:1 via the main jets. Another track tip includes logging the RPM drops between gears. Previous logging showed that we could stay on the fat of the torque curve after each gear change by narrowing the gear splits, so we changed from a Tremec wide-ratio 3.27:1 first gear trans to a close-ratio with a 2.95:1 first gear.

Instead of a run-by-run view of each line graph, you can very easily combine all of your passes (sessions) and look at them in a table or as a chart. Create a table in LogWorks's graph by clicking "View," then "View Chart" and configuring your table axes (Horizontal = RPM, Vertical = Vacuum or MAP, Chart Content = LM1_02). To collapse all the sessions, click on Sessions. The table below is based on the same data as the dragstrip run, and it highlights the lean Air/Fuel Ratio condition during wide-open-throttle (low Vacuum / under 1.58 PSI) over 5000 RPM as orange or yellow color-coded cells.

7. Cruise Tuning: Many tuners think that main jets control most of the fuel flow during cruise RPM – 2100 to 3400, depending on gearing. The reality is that the idle circuit on most carburetors can control most of the Air/Fuel Ratio during steady-state cruise, yielding better fuel economy. Using the Innovate LogWorks software, you can find the transition period between the idle circuits and the mains fairly easily, and then optimize the idle circuit as an "idle/cruise" circuit and let the mains & power valve specialize on high load, wide-open-throttle situations. A dyno is the safest and most repeatable place to do this type of tuning, but you could drive your car on a long, flat stretch of road to capture the data as well.

Assuming you've properly set up your idle circuit in the 13:1 to 14.5:1 Air/Fuel Ratio range for zero load (parked) idle and partial load (under 1900 RPM), try temporarily jetting the mains over-rich. Go up 4 - 8 jet sizes just for this exercise, giving you between a 10:1 and 11:1 Air/Fuel Ratio at 4000 RPM 3 rd or 4 th gear steady state cruise. With the car on the dyno or on a flat road, run it up to 4000 RPM in 3 rd or 4 th gear, then start recording the session on your Innovate equipment. Begin dropping RPM in 250 RPM increments from 4000 RPM and then holding that RPM for 10 seconds each time: 4000, 3750, 3500, 3250, 3000, 2750, 2500, 2250, 2000, 1750. Download this data to your laptop and look at the Air/Fuel Ratio for each 10 second RPM sample. When the Air/Fuel Ratio begins to rise on that chart (from the 11:1 range to the 13:1 range), the mains are transitioning back down to the idle circuits. On many cars this occurs between 2000 and 2500 RPM.

An additional way of looking at this data is through the LogWorks Table and Chart facilities described earlier. The chart below shows a good cruise Air/Fuel Ratio (in the 14:1 range) attained at varying load ( Vacuum ) conditions between 2100 RPM and 2400. Note that lower vacuum (higher load) conditions brought the Air/Fuel Ratio down just below 14:1 while lighter loads had it near 15:1.Not bad for a 560 HP pump-gas Camaro that runs 11s in the quarter and gets 21 MPG.

Depending on what RPM and Air/Fuel Ratio your car cruises at on the highway and if you have adjustable air bleeds for the main jet circuits, you can begin incrementally trying larger air bleeds to delay the RPM onset of the mains. This may slightly lean out the mains' Air/Fuel Ratio as well, so be careful during this phase if you choose to work with the high speed (main jet) air bleed circuits.

Use the LogWorks View / View Chart facility to build a table for each set of high speed air bleeds you data log. The table facility in LogWorks allows you to highlight and copy these tables into tabs on a spreadsheet, so you can calculate the difference of your setups on a third tab to see the effect of your changes. In the example below, we changed the high speed air bleeds on a Demon carburetor to delay the onset of the main jets during cruise. This tweak improved Air/Fuel Ratio in the car's cruise range (13 PSI through 16 PSI, from 2000 RPM through 2500) as shown in the green highlight. (This table is the difference in AFR between the two runs).

Once you have the mains coming on closer to the RPM level you want, you then need to double check Air/Fuel Ratio through the full range that the mains are operating to ensure you're not getting too lean. If you are too lean, increase the size of the main jets to achieve a decent Air/Fuel Ratio . Be careful and incremental here, listen for any signs of detonation and remember to not delay the onset of the mains too far (resulting in flat spots). 2800 RPM is the upper limit for delaying the onset of the main jet system, especially if your engine combo is set up for a low torque peak with high compression & a smallish cam. Remember to make one change at a time, measure the results, and repeat. Soon you will be "finding" horsepower and efficiency in all sorts of unexpected places!

Old School Meets New School :How to Get EFI-Quality Mileage From Your Carburetor

Think you can't have a small-block that lays down 556 hp, 512 lb-ft of torque, 120-mph trap speeds, and 21 mpg on the highway without dropping three grand on a slick EFI setup? Think again.

The secret? Wideband tuning and adjust-able carburetor fuel circuits that allow you to tune idle/cruise mixture and curves. "Off-road use only" combinations of cam-shaft, cylinder heads, and quench area can become surprisingly docile with some attention to carburetor tuning. Most over-the-counter (OTC) carbs come with a tuning baseline that will run OK in the average car, but not exceptionally well with your specific application. With wideband tuning and careful attention to two key circuits found in most OTC carbs, you realize fuel mileage that rivals that of the latest EFI setup. Yes, having an overdrive to slow the final drive ratio down to the 2.5:1-2.6:1 range helps, but the mileage benefits of a 2,000-rpm cruise can be easily nixed by an untuned carb dumping a 10:1 air/fuel ratio into the motor when 15:1 is nice enough.

Most people think of tuning a carburetor via two circuits: the mains and the idle mixture. For this article, we're going to go way deep on the idle circuit and ignore the mains/wide-open throttle. Contrary to popular belief, the mains don't really come into play until engine speed reaches 2,500- 3,000 rpm and assumes a low-vacuum mode, like when your right foot is getting acquainted with the carpet.

The often-overlooked idle circuit determines the idle mix, as well as cruise and part-throttle efficiency. Get the idle air/fuel mix in the 14-15:1 range at idle, transition, and cruise, and you're way ahead of a carburetor that dumps 10-11:1 buckets of gas through your motor. During light load conditions, your engine can get by fine on 14 to 15 parts of air for every part of fuel (6.8 percent of the mixture by volume), which equates to 33 percent less than an 11:1 air/fuel ratio.

WHAT YOU'LL NEED:

* Innovate Motorsports LM-1 Wideband tuning device and LMA-3 Aux Box data acquisition (roughly $590)

* Idle-feed restrictor blanks ($14, Barry Grant PN 200083, drill to size)

* Air bleed blanks ($13 for Barry Grant PN 200082 or $26 for Holley 126-28-10, drill to size)

* Small drill bits, 0.018-0.100-inch ($20 per set from most hobby/remote control shops)

* Power drill and small bit chuck (to handle the very small drill bits)

* Narrow-blade standard screwdriver (for changing air or fuel bleeds)

* Line wrenches and Allen- or screwdrivers for removing fuel bowls

* New bowl and metering block gaskets (replace if old or questionable)

* Small snack bags (to hold IFRs or ABs separately)

* Sharpie permanent marker

BASELINE

First, make sure that the primary and secondary throttle blades uncover 0.020 inch of the transfer port. This is standard procedure with most Holley and Demon-style carburetors and is usually done before putting it on the manifold so that you can visually check and measure the amount of transfer port being uncovered.

On a four-corner idle circuit carb, you may be able to gain some idle speed by opening the secondary throttle-blade position a hair. If the engine still doesn't have acceptable idle speed and quality, you may consider drilling a 3/32­inch (0.09375) hole in the throttle blades. Mighty Demons, such as the one used on our test car, offer an alternative to drilling the blades. You can increase the idle air allowed into the engine via its Idle-Eze adjustment found underneath the air-cleaner stud.

Next, gently rotate the idle-mixture screws clockwise (on both sides of the carb, or on all four corners if your carb is equipped with four-corner idle circuits) until they're fully seated--don't over-tighten. With all four idle-mixture screws seated at zero-air/fuel admission, back each one out 1.5 turns counter-clockwise. This will give you a base- line amount of air/fuel being admitted to the engine at idle and allow you to get the car started and running. After you start the car, you may have to adjust the idle-mixture screw outward (counter-clockwise) or inward (clockwise) by as much as a full turn to keep the engine idling.

Look at the Innovate LM1 readout at this time to check the air/fuel mixture. For now, aim for 13.5-14:1 to get the engine up to operating temperature. The air/fuel ratio will richen up as the engine reaches operating temp. Once it's fully warmed again, adjust the four idle/cruise-mixture screws until you're in the 14.0-14.4:1 range at idle. Ideally, you'll also have the Innovate Aux Box set up so you can monitor engine vacuum, rpm, and acceleration (more on measuring acceleration later).

Using the LM1 wideband monitor and Aux Box data acquisition really makes this step simple, since you can maximize the screen on your laptop while the LM1 is attached, and adjust the idle/cruise-mixture screws (for air/ fuel) and Idle-Eze screw (for idle speed and air/fuel). The LM1 and Aux Box provide you with six exceptionally easy-to-read gauges, enabling you to tune a solid idle, a higher idle vacuum, and an air/fuel baseline of 14:1. The high-visibility dials (see close-up) make it easy to immediately see subtle changes to air/fuel ratio, idle rpm, and manifold vacuum in real time, while you're tuning the car. Now check the vacuum reading at idle. Our hot-cam small-block (253 intake, 259 exhaust duration at 0.050 and 0.640-inch lift, 110-degree lobe separation) idled at 9-9.5 inches at 820 rpm. With this in mind, we installed a 6.5-inch power valve, allowing the engine to get a healthy splash of fuel when engine load (vacuum) dictated it. Since it's only 3 inches below idle vacuum, this is a fairly loose power valve. We're on the lean edge of idle/cruise while also delaying the onset of the mains. So having a power valve 3 inches below idle vacuum has proven to keep throttle response crisp without dumping in fuel. Most tuners would stop at this point and begin jetting the mains. But hold on--here's where we improve fuel economy and provide razor-sharp throttle response.

ENHANCED TUNING

The first tool in the enhanced tuning section is the Idle Feed Restrictor (IFR), which is located in the metering block, so you'll need to drain and pull the fuel bowls to get at it. If you have a four-corner idle/cruise carb, there are two diagonally oriented removable bleed/restrictors on the primary metering block and two on the secondary side. The IFR is the gatekeeper of fuel for the idle/cruise circuit. Experienced tuners decrease IFR size when they need to reduce idle/cruise below 1/2-3/4 turn from fully closed in order to get 14:1 air/fuel ratios at those speeds. The IFR is flooding the idle circuit with fuel and causing the idle and cruise to saturate. Alternatively, tuners can increase IFR size if the engine is starving for idle/cruise fuel (beyond 2.5 turns out from fully closed/seated idle/cruise screws to keep the engine running). Graphics always tell the story well, so here's a look at Innovate's Logworks data logging facility. As the car crests a hill, notice the blue manifold-vacuum line rising as the idle/cruise air/fuel mixture falls into the 11-12:1 range. Leaning out the IFR should help these lines move in parallel instead of opposite directions, as seen in this diagram.

Our test car yielded idle mixtures in the 13:1 range when there was very light load at cruise, but when the load changed, the ratio plunged to the 12s and 11s. Pig rich. With the stock/OTC 0.036-inch IFR in our 750-cfm Mighty Demon, we couldn't out-mpg a Ford Excursion. To compensate, we dropped the IFR from 0.036 to 0.020. Since we'd cut so much fuel out of the circuit, even with the idle/cruise screws backed out from 1.5 to 3 turns, the engine would barely idle or run under 2,000 rpm. This meant we had succeeded in limiting fuel flow through the idle/cruise circuit. The next step was to change the rpm and rate at which the idle/cruise circuit allowed admittance to the new and thrifty metering curve.

We then began adjusting the second component in the idle/cruise circuit, the Idle Air Bleeds (IABs). IABs are small screw-in "air jets" that reside in each barrel of the carburetor--they are the ones farthest away from the fuel vents in the Mighty Demon, as shown in the accompanying diagram.

IABs function as a mini-carburetor within the idle/cruise circuit. They take the fuel from the IFR and bleed in a small amount of air under vacuum, before this air/fuel mix makes it to the last step into the engine (the Idle/cruise­mixture screws). The IABs allow you to tailor what vacuum/load and at what rpm the idle/cruise circuit will begin to meter air/fuel to the engine. With our engine starving for air/fuel, thanks to the ultra-lean IFRs we'd just installed, we had to make our leaner air/fuel curve come on-line earlier via a smaller IAB hole. The stock IABs are 0.070 inch; we went down to 0.032 inch. With the smaller IABs, the car fired right up and idled with the idle/cruise screws 1.6 turns out from seated. We set the air/fuel at 14.3:1 on a warmed-up idle, and the engine ran perfectly at 14.0-14.7:1 from 1,400 to 2,100 rpm (part throttle through the gears as well as cruise).

The next step was to rein in the mains. They were beginning to make the air/fuel mixture go rich under load (14 inches of vacuum at cruise or less) or above 2,500 rpm. The idle/cruise circuit was now doing its job flawlessly, but the main circuits were ready to join the party too early under those same conditions. Air/fuel would fall to high-11s and mid-12s at 2,300 rpm or under load.

Since we had just enabled the idle/cruise circuit to function from 900 through 2,900 rpm, we didn't need the mains joining in at 2,400 rpm. We remedied the over-rich condition in the mid-range cruise by retarding the mains' high-speed air bleed (HSAB) circuits from coming in as soon--the opposite of what we did with the IABs. Since the mains were allowing fuel to come in too early, we opened up the HSABs from the stock 0.039s to 0.093s. The jumbo 0.093-inch HSABs delayed the onset of the main circuits to 2,800 rpm, as shown in the green and blue bars in the accompanying charts.

Sure enough, the 0.093s kept our air/fuel in the low-14s all the way up to 2,600 rpm on level ground and helped keep it in the high-13s when pulling up hills or accelerating lightly. The chart below reveals our final state and illustrates our improvement in air/fuel at cruise from the mid- 13s to the mid-14 range, pulling 200 more rpm at cruise and the same vacuum. No stumbles and no hitches, other than the occasional tapping of the fuel gauge just to make sure it hadn't frozen up. The trip back from the race track had us with traffic running 65-70 mph, and we saw 21 mpg when we filled up back at home.

Car Craft July 2005

You'll Need Some Electronics to Do It, but Now It's Easier Than Ever to Be A Carb-Tuning Hero

By Jeff Smith

In a time not long past there was that guy down the street from you – that special car-crafting guru who could tune an engine by ear. He was revered by the local gearheads for his uncanny knack for creating not just impressive power, but also transforming chugging street slugs into razor-sharp sweetheart engines. He was like the Pinball Wizard – the deaf, dumb, and blind kid who could play those flipper fingers like he was part of the machine. We were all in awe of the Carb Wizard. While that guy still exists, we've discovered a little piece of electronic technology that can turn almost any knowledgeable car crafter in a Carb Wizard. This latest development in hand held electronic-power knowledge is the affordable air/fuel-ratio meter. While there are many on the market, we first ftold you about a favorite, the Innovate Motorsports digital unit, in "Tune In, Turn On, and Make Power" (Feb. '04) where we explain how it works alongside a few basics concerning air/fuel ratio and horsepower. This is such a potentially great tool that we thought we'd get into how to tune your engine using this tool not just for max power, but also to raise the bar for better part-throttle response and highway cruising. While the innovate meter is capable of logging up to 44 minutes of brain-numnbing data, we'll approach this tuning session assuming you're going to read the Innovate meter in real time. Ideally, data logging is better because you can study the information more closely.

WOT

The best place for wide-open throttle (WOT) air/fuel testing is at the dragstrip. Short of that, you can do Second-gear bursts of 2 to 3 seconds each and have a passenger watch the meter. For your initial work, you should shoot for WOT air/fuel ratios between 2.5:1 to 13.0:1. Remember to make only one change at a time and keep using the same test procedure. If you're at the dragstrip, use mph numbers to help with tuning trends. As long as your changes improve trap speed, continue to move in that direction. IN many cases, the combination will be rich – like 11.8:1 at WOT. That means you should start by leaning out the secondary side of the carburetor. With Holleys and Demons, minimum jet changes of two sizes per step are a good idea. For example, if you want to run leaner , go from 80 rear jets to 78s. It's also a good idea to start your tuning with the carb in its stock jetting configuration. IF you are five or six jet sizes (or more) away from the box-stock configuration, it's possible there's something else wrong with the carb or your engine.

PART-THROTTLE TUNING

Contrary to what you may think, street engines spend a majority of time at idel and at very low throttle openings. In addition, the idle cicuit continues to deliver fuel even when the carb is delivering fuel through the main metering circuit. Given this, the best place to start improving highway and in-town fuel mileage is with the idle circuit.

Most general-purpose aftermarket performance carburetors are designed to deliver around a 12.5:1 air/fuel ratio to avoid lean surge conditions. Most mild street engines can tolerate part-throttle air/fuel ratios of 13.5:1 all the way up to as high as 15.0:1. Keep in mind that all production EFI engines operate 14.7:1 air/fuel ratio and the driveability is excellent. It's more of a challenge to tune a carburetor to achieve a lean 14.7:1 air/fuel at part-throttle and still deliver excellent and immediate WOT power, but it can be done. What this means is the power-valve and accelerator-pump circuits become much more critical. This is where a Q-jet shines, using its small, highly responsive primary side to achieve excellent throttle response for part-throttle driving. But other carbs can be tuned to also work very well. Don't be afraid of 14.0:1 or even 14.5 – 15.0:1 air/fuel ratios, they don't hurt the engine. There is very little load at highway cruise speeds because the engine is only making about 15 to 25 hp under these conditions.

This is definitely cut-and-try type work. IF you go too lean on the idle-feed restrictors, the engine will surge at cruise and hesitate under light acceleration, since most engines don't like to accelerate at lean air/fuel ratios. If you tune the idle-feed restrictors too lean, the engine will most likely suffer from an off-idle lean stumble as an early indicator that you've gone too far. It's the transition circuits that are more seriously challenged and the ones that will falter first when you begin to lean out the idle and primary main circuits.

TUNING CHALLENGE 1

Our first real-world example started out with a 9.0:1 compression 455ci Olds with a mild hydraulic cam, dual-plane Edelbrock, the stock 455 Q-jet, headers, and an HEI ignition. The Innovate meter reported an idle mixture of around 12.0:1 that went lean at about 13.8:1 as the throttle opened up in mild acceleration. At steady-state highway cruise speeds, the air/fuel ratio went back rich at around 12.5:1. At WOT, the engine was actually a bit lean.

The first thing we did was to adjust WOT tuning by swapping the stock CH secondary rods to thinner rods (eventually a pair of aluminum rods) until we had a WOT air/fuel that came in around 12.8:1. Because of the cam, intake, and header swap, part-throttle transition fuel was also slightly lean, so we changed to a slightly weaker power- valve spring to pull the metering rods out of the primary jets sooner as load increased. The engine responded with a slightly richer mixture in light acceleration of around 13.2:1, but we still had a slightly rich cruise air/fuel ratio. When we tried larger (leaner 52B) primary metering rods, it hurt light-throttle acceleration. Some late-model Q-jets are set up to allow you to adjust the position or depth of the primary metering rods in the jets. If our carb had been equipped with this feature, we could have adjusted the metering rods deeper in the primary jets to lean out the part-throttle metering.

TUNING CHALLENGE 2

We also tried a 350 Chevy equipped with a long-duration cam and a Holley 750-cfm 0-3310 vacuum-secondary carb that suffered from a bad off-idle stumble and a pig-rich 10.5:1 ratio at part-throttle cruise. The WOT air/fuel ratio was only slightly rich at 12.2:1. The challenge was to improve the driveability and mileage without sacrificing WOT power. After properly adjusting the primary accelerator-pump linkage, the stumble disappeared. We also replaced the large 0.036-inch accelerator-pump nozzle to a 0.028 to further improve the throttle response.

The LM-1 meter told us the engine was way rich at just off idle, so we first tried leaning out the idle-mixture screws, but it didn't help. Next we disassembled the carb and found that a previous hacker had drilled out the idle-feed restriction of around 0.032 to 0.035 inch. Some quick math revealed that the 0.052-inch orifice increased the area by more than 100 percent. As a temporary fix, we tried a 0.020-inch-diameter wire stuffed into the idle-fuel jet to reduce the flow area. The larger wire reduced the area by roughly 15 percent, which leaned out the part-throttle air/fuel ratio to roughly 11.8:1. which was still very rich. Further experimenting with reducing the main jets from 72 to 69 and using a slightly larger 0.025-inch wire in the idle-feed jet finally got the part-throttle air/fuel ratio close to 12.8:1. We could not tune any leaner without creating an off-idle stumble and part-throttle lean-surge condition because of the cam. The WOT air/fuel also improved the leaner primary jetting to 12.5:1. These simple changes improved the fuel mileage by over 30 percent.

An ideal accelerator-pump shot is just enough to maximize acceleration. Additional fuel only kills power.

The best approach is to weld the supplied bung into the exhaust pipe near or in the header collector. Mount the Bosch sensor in the upper half of the pipe to prevent condensation from affecting sensor accuracy.

Part of the Aux Box software allows you to custom configure up to five gauges on your laptop such as air/fuel, an rpm signal, and a total of four other 0-5-volt analog channels for stuff like voltage, engine temperature, engine vacuum (MAP), and throttle position. This data can be viewed in detail to help you dial in the car.

WOT tuning is relatively simple. If the meter reads richer than 12.5:1, remove the secondary float bowl on your Demon or Holley and try jets two steps leader. Shoot for between 12.5 and 12.9:1 air/fuel or for top dragstrip mph.

Rochester Q-jet WOT is the easiest to tune. All you have to do is change the metering rods. Fatter rods are leaner (less fuel)while thinner metering rods flow more fuel for a richer mixture.

The Edelbrock carb primary metering rods and springs are incredibly easy to change. Merely loosen the lid screw, slide the cover over and pull the rod and spring out. If you need to change primary or secondary jets, the lid must come off, which only takes a couple of minutes and you won't spill any fuel.

The Q-jet uses one power-valve piston with a hanger to operate both metering rods in their respective primary jets. A stiffer power-valve spring pushes the metering rods out of the jets sooner (at higher vacuum levels). A softer power-valve spring uses less fuel by keeping the metering rods buried in the primary jets.

Setting idle mixture will change when you bolt on the air cleaner. If possible, set your idle-mixture ratios with the air cleaner in place. Holley and Demon carbs use a diaphragm-style primary power valve. The opening point is usually marked on the valve, such as a number like 65. This means that the valve opens (adding more fuel) at 6.5 inches of manifold vacuum. Using a lower-number power valve, like a 55 or 45 delays power-valve opening and could improve fuel mileage.

While the idle circuit is very basic, it has a huge impact on drieability. The idle- mixture screw controls the idle air/fuel mixture, but once the throttle is open the idle fuel restrictor combined with an idel air bleed determine the off-idle air/fuel ratio until the throttle blades open enough to create fuel flow out of the boosters and the main metering circuit.

Big cams with low idle manifold vacuum require opening to flow sufficient air to make the engine idle. If the throttle blades expose too much of the idle transfer slot (arrow) at curb idle. Then the usual fix is to drill two small holes (starting at around 3/32 inch) in the primary throttle blades on the idle-port slide of the blades. This shows the proper amount of the idle transfer slot exposed.

CC Tuning Tip

Poor ignition performance can be confusing when using the LM-1 air/fuel ratio meter. When a cylinder misfires, the air and fuel do not combust, meaning the oxygen in the air moves into the exhaust where the O2 sensor will immediately pick up the additional air and indicate a lean condition. Simply put, this means a dead cylinder or occasional misfire will show up on the innovate meter as a lean condition not a rich mixture as you might thing. Fix the misfiring cylinder(s) and the air/ fuel ration will read as a richer mixture.

True Reading

Excerpts from Muscle Car Enthusiast, September, 2004, by Dave Dudek, Jr.

There are several methods people use to get their machines tuned propoerly, and each method offers strengths and weaknesses:

• You can measure the exhaust gas temps (EGTs) on each cylinder. This is done by welding a bung in your header or by drilling and tapping your exhaust manifolds about one inch from where the exhaust exits the head. This method measures the temperature of the exhaust gases as they exit the cylinder head. This method of tuning is very time consuming and generally expensive -- most weekend enthusiasts will never go to this extreme to tune their cars.
• A more commonly known tuning technique is "reading the plugs." This might be the most abused and misunderstood tuning tool used. A professional can tell plenty about how your engine is tuned by reading the plugs, the key word being professional
• Another device used to help aid in tuning is a "narrow band" analog rich/lean gauge. This device uses an oxygen (O₂) sensor. However, because of the narrow volt range of zero to two volts, many consider this to not be accurate and many professionals discount it completely.

To test the LM-1 meter we took our 1970 Challenger R/T test vehicle to AP Engineering Clinton Township, Michigan. AP Engineering is one of the premier dyno and tuning facilities in the state of Michigan, and they just happened to have a high-dollar profession-grade wide band O2 setup. What better way to test the accuracy of Innovate Motorsports' new product?

When we fired up the Hemi and made our first dyno pull, the LM-1 meter showed the air/fuel ratio was 11.4 (way rich) at peak power (501 hp). We then switched from the LM-1 meter to AP Engineering's professional wide band set-up and made another pull. Everybody was floored when the computer spit out 11.3 at peak power -- the LM-1 was almost dead-on! Peak power was 501 again.

A reading of 11.4 is rich, so we put smaller jets in the carbs and made another pull. Horsepower jumped to 522 and the AFR hit 12.3 at peak hp. Again, we swapped in the LM-1 meter and made a confirmation pull. The LM-1 was dead on at 12.3. That number is still rich so we made another jet swap and fired up the Hemi once again. We were rewarded with 531 hp and the A/F securely at 12.9. Again we swapped back to AP's pro set-up and another pull confirmed the LM-1 was almost dead on.

Dial in the Perfect Air/Fuel Ratio in Your Driveway

Tuning our '67 Firebird with the LM-1

[excerpts from High Performance Pontiac. October, 2004]

by Rocky Rotella

The carburetor is one component few enthusiasts fully understand. Since it is ultimately responsible for providing the engine with the correct mixture of fuel and air at every rpm point, having it too rich or too lean in one or several areas can negatively affect the perfomance of the vehicle. Installing different-size metering jets and/or rods can produce improved results, but dragstrip testing or expensive dyno sessions remained, until recently, the most accurate ways to find the perfect combination for maxiumum performance.

Our Test Car

We felt our '67 Firebird convertible would be an excellent candidate to test the functionality and versatility of the LM-1. Our Firebird features a basic performance rebuild using stock-type parts with part-throttle street manners receiving as much attention as full-throttle performance. The original 400 was removed and replaced with a 455 now displacing 462 ci. It features mildly ported 4X heads with 2.11/1.77 inch valves, a compression ratio just over 9.75:1, a Nunzi hydraulic camshaft with 222/232 degrees duration at .050, an Edelbrock Performer RPM intake manifold, and a '77 Pontiac 800-cfm Quadrajet. The combination is rounded out with four-tube headers followed by a Flowmaster exhaust system and a Turbo 400 backed by a limited-slip 3.55 rearend. It feels strong under all types of driving conditions, and in many respects it represents a wide variety of combinations seen on the streets today.

Getting Started

Our first step in testing was to connect the LM-1 to a 12-volt power source and calibrate the 02 sensor to open air as stated in the instructions. Once calibrated we inserted the probe into the tailpipe, and with our engine running at normal operating temperature, we viewed the readings. We knew our car was slightly rich at idle by the smell of raw fuel from the exhaust, and our suspicions were confirmed with an A/F ratio of about 13.2:1 at idle. Before making any changes, we took our Firebird for a test drive, noting the A/F ratio under the diferent types of driving conditions it sees and allowing us to accurately view the effects of the changes we might make.

We quickly found our car was running around 12.5:1 under aggressive, part-throttle conditions with a slight cruise ratio near 14:1. We also found our full-throttle A/F ratio to be near 11.5:1, which is a bit rich according to the experienced sources we contacted.

Using the LM-1 as a Tuning Aid

We then directed our attention to the carburetor. Since the Quadrajet has separate primary and secondary circuits, each can be tailored independently to produce the best total performance while on the respective circuit, giving the best overall throttle response in all types of driving conditions. For the most accurate results we opted to tune each circuit independantly, limiting our first changes to the primary side, then addressing the secondary side.

Knowing the A/F ratio was 13.2:1 at idle, we readjusted the idle mixture screws located in front on the base of the Quadrajet. This leaned the idle ratio to around 13.5:1 but had little effect on part-throttle readings. Wanting to lean the part-throttle ratio, we replaced th existing .074-inch primary metering jets with leaner .072 jets. This allowed us to further trim our A/F ratio to around 14.7:1 at idle, and the test drive immediately after proved this was a step in the right direction. Throttle response had noticeably improved and our engine was more sensitive to throttle position changes making the car easier to drive. The LM-1 agreed, now showing our light cruise mixture around 14.5:1 with aggressive part-throttle near 12.8:1.

Since its rebuild our carburetor has been running secondary metering rods with a 0.35-inch tip with satisfying results. With the initial test drive we knew the full-throttle A/F ratio of 11.5 was slightly rich and leaning it might produce a more complete burn. Wanting to place the ratio closer to 12.5 to 13:1, we selected rods with a tip diameter of .044 inch, which leaned the ratio to around 12.2:1. Since we are trying to extract maximum efficiency from our combination and hoping to lean it further, we installed secondary rods with a .0527-inch tip, which improved the full-throttle A/F ratio to 12.7:1 and within our target range. Acceleration felt more brisk, especially at the point the secondary air valve began to open, which are the results we hoped for.

Conclusion

While experienced tuners could achieve similar results with minimal trial and error, the LM-1 gives the backyard mechanic an opportunity to tune his or her Pontiac to perform equally well. To some it may first appear to be a race-only tuning tool, but we quickly saw how beneficial the LM-1 can be for street cars, and having your car perform better under all types of driving conditions is never unpleasant. It might take supertuning your Pontiac to the next level!

Tuning a Marine Carb

Excerpts from Family & Performance Boating, by Henry Olsen

Summer is here and gasoline prices are up and out of sight, this has many boat owners wondering how they tune their engine so they can get more hours out of a tank of fuel without losing power or doing any engine damage from going to lean on the air/fuel mixtures. Properly tuning a carburetor or programmable fuel injection to supply a boat engine with the correct air/fuel mixture for performance, lower fuel use and reliability has always been thought of as an art that those few people that can "read" a spark plug could do properly. Those top tuners looked at the spark plug, the exhaust port and the first 6 inches of the header for proper "color" and then made an educated guess at what jet size change was needed. One of the disadvantages of this method is that the header and spark plug can only indicate what the mixture was at the exact rpm and load condition the plug check was done at, so you were mainly just tuning by trial and error. The more modern day tuners are now taking advantage of the technology being used to make today's new boats run so good by the use of a wideband oxygen sensor to read the content of the engine's exhaust. A wide-band oxygen sensor reads the oxygen or unburnt combustionables content of the exhaust to determine the air/fuel mixture. This new wideband oxygen sensor technology is being used by the top race teams in Nascar and NHRA Pro-Stock as well as some of the top Super Cat off-shore race teams.

The proper tuning of any engine can make the difference between a great running engine and an engine that always sounds and runs like it needs a "tune-up". For most marine tuners, one of the biggest mysteries is how do you "jet" the engine in order to obtain the correct air/fuel ratio necessary for a high performance marine engine, to not only supply drivable horsepower when you want to go fast, but also supply the engine with the correct air/fuel mixture for while just cruising or when idling thru a no wake zone.

Tuning with a Digital air/fuel meter.

The air/fuel meter method uses a wideband oxygen sensor to determine the fuel mixture by analyzing the unburned combustibles in the exhaust gas. A wideband oxygen sensor can read air/fuel mixtures as rich as 9 to 1 or on the lean side it can read air/fuel mixtures lf 19 to 1 or leaner (a standard, narrow-band oxygen sensor is only accurate at air/fuel mixtures of around 14.7 to 1). This method has the advantage of extremely fast reaction times for the readings but the accuracy of the readings can be affected on an engine with a "race" cam or a supercharged application at light load/low rpm testing conditions because of the excessive oxygen in the exhaust created by the cam overlap or the superchargers blow thru effect at low engine speed and low load conditions. The digital air/fuel meter method requires you to know what air/fuel mixture your engine needs for each driving condition.

A starting point for air/fuel mixtures for most performance marine engines is:

Idle: 14.1-13.4 to 1 air/fuel mixture

Cruise/light loads rpm 14.2 –14.0 to 1 air/fuel mixture

Power mixture and acceleration: 12.5 to 1 is the ideal air/fuel mixture for a "normal" engine, but many marine engine builders prefer a 11 or 11.5 to 1 power mixture; a high performance engine with improved combustion chamber design such as a Pro-Stock or a Winston Cup engine, which are being used in some of the top offshore race boats, can use a slightly leaner power mixture of 13.0 to 1 air/fuel ratio. A supercharged engine can use a power mixture richer than 12 to 1 as a method to help control the detonation that can be caused by the higher cylinder pressures.

The performance and replacement marine carburetors sold today have a generic "tune-up" or jetting unless the carburetor is built for a specific engine package and fuel. A carburetor not built and tuned for a specific engine, exhaust system, and fuel should supply an air/fuel mixture rich enough for a variety of engines (but this is not always the case). If the carburetor is supplying too lean of an air/fuel mixture, the engine will lack power, run sluggish, overheat and the lean mixture could cause engine damage. If the carburetor is supplying an air/fuel mixture that is too rich, the engine may tend to load up, foul the spark plugs, run sluggish and lack power. The carburetor must have 5 ½ to 6 ½ lbs. of fuel pressure at all rpm and load conditions, if the fuel pressure goes to high the carburetor will tend to" flood", while if the fuel pressure goes to low the carburetor fuel level will drop causing the engine to starve for fuel at higher loads and engine speeds. If the fuel pressure drops below the proper pressure, the carburetors air/fuel mixture will go lean and engine damage may follow. A fuel pressure in excess of 6-½ lbs. can cause the carburetor to flood especially when operating in rough water conditions such as when you jump a wake or if you land in the trough after coming off a large swell, this flooding can be seen as black smoke coming from the exhaust or the engine begins to miss and run sluggish till it clears out.

One area often ignored is fuel tank venting, if air can not get into the tank to replace the fuel the engine is consuming fuel can not get out, the fuel tank must have a vented gas cap or some other type of vent system. Doug Schriefer from Barry Grant Inc. often points out that for every gallon of fuel you use a gallon of air must be allowed into the fuel tank so if you are adding power into your boat you may need to upgrade the fuel tank vent system with larger hoses or additional vents. If the fuel tank vented by a hose routed to a external vent always be sure to route the hose so it has a loop in it that is above the external vent, this will keep any water spray from traveling from the vent thru the hose and into the tank because the water will not easily travel up hill. Also do not forget to upgrade the fuel filter/water separator, you are operating in a marine environment and water is everywhere you need to keep the water out of the carburetor or fuel injectors. Proper fuel pressure/volume and fuel tank venting are very important because a marine engine is expected to supply more power for a much longer time than any other form of Motorsports, the fuel pump must be able to supply enough fuel for the carburetor while the engine is supplying the boat with full power for sometimes hours at a time!

The fuel you use (reformulated pump or race), the air density (i.e. altitude, barometric pressure, air temperature, humidity), compression ratio, camshaft, exhaust system, ignition timing curve, engine condition, fuel pressure, air flow thru the flame arrester, etc will all effect the carburetor "tune-up" needed to get the correct fuel mixture for your engine. The first order of business is to get the correct ignition advance curve for the engine and fuel being used, then the fuel pressure must be checked to be sure it has the proper system pressure at all engine load conditions. Too much or too little ignition timing can give you a false lean or rich air/fuel ratio reading, so first check and set the ignition advance and advance curve!

Ignition Timing and The Advance Curve

Before checking the air/fuel mixture, the ignition timing and advance curve must first be correct. No mater how what ignition system you use, if the ignition spark timing is not correct for the engine needs, the engine will not produce all the potential power built into it. Once the ignition advance curve has been confirmed to be correct, many of the problems that we see can be traced to the fuel mixture being incorrect for the engine's needs.

Checking the air/fuel mixtures under load with a carbureted engine

After the basic engine condition and tune-up (fuel pressure, timing curve, etc) is confirmed to be correct, the next step is to determine what the air/fuel mixture is at idle through 3000rpm. If the cruise mixture is off, first change the jets in order to get the air/fuel mixture correct at the 2500-3000-cruise rpm range. Then check and set the idle mixture. If the air/fuel mixture is too lean at idle or part throttle and the idle mixture screws do not provide enough adjustment, the correction may involve enlarging the idle "jet". This lean condition at part throttle condition will cause the engine to miss or stumble, this is due to the lean air/fuel mixture, this problem is very common on many of the performance carburetors sold today. If the air/fuel mixture is too rich at idle and part throttle, the idle jet/restriction may be too big and may need to be replaced with a smaller one.

The next step is to read the air/fuel mixture while operating the boat under power using a wideband oxygen sensor to check the cruise speed air/fuel mixture-main jetting, followed by a check of the power air/fuel mixture under load. During a drive test you are able to read and then correct the air/fuel mixture so you can have them correct at idle, cruise/light throttle and full throttle. If you are buying a engine package that has been "dyno tuned" or developed and run on an engine dynamometer, get the engine builder supply you with what air/fuel mixture they ran the engine on the dyno for both maximum power and cruise rpm loads and then be sure they are the same with the engine in the vehicle. If you have a engine builder build a custom engine for you and they run it on a dyno, have them record the air/fuel mixture with a air/fuel meter such as the Innovate Motorsports unit and then you can use the recorded data to tune the fuel curve to supply the engine with the same air/fuel mixture that the engine builder used on the dyno. Many of the engine packages we have checked the ignition spark timing and air/fuel mixture curves on have had the correct ignition spark timing and air/fuel mixtures for high rpm/wide open throttle operation but need a lot of tuning work at low rpm/part throttle/normal driving conditions. In most cases when an engine is run on a engine dynamometer, they only check for maximum power while using race style headers with open exhaust (non water jacketed marine headers) and they supply the engine with air that is not of the same density the air you will see when your boat is in the water and the carburetor probably did not have a flame arrestor or any other type of air cleaner on it.

The air/fuel mixture and ignition timing curves should be corrected for the real world operating conditions of your boats engine compartment with coming thru your flame arrestor, along the changes in exhaust backpressure created by the exhaust system you are using which may cause the air/fuel mixtures to change from their original baseline causing the engine to not perform with the same power that was seen on the dyno.

Tuning A Fuel Injected Engine

The Innovate Motorsports wide band oxygen sensor based air/fuel meter can be used to read the exhaust in order to be sure the air/fuel mixture that a fuel injection system supplying is correct for the engines demands. If the fuel injection system is programmable the correction may be as simple as a few simple computer program changes, but if it is not programmable there is still a few tricks that can be done. The easiest way to change the air/fuel mixture on a non-programmable fuel injection system is to change the fuel pressure or the flow rate of the fuel injectors. As the fuel pressure is increased the fuel flow will be increased, thus making the air/fuel mixture richer. Increasing the fuel pressure has a limited effect on fuel mixtures, if you increase the fuel pressure too much the fuel injectors windings may not have enough power to open the fuel injectors against the increased fuel pressure, this will cause the mixture to go lean as the fuel injectors start to lock closed. If you need to increase the fuel pressure from a base fuel pressure of 40 psi (pounds per square inch) more than 15 % to try to get a rich enough air/fuel mixture, it may be time to buy larger fuel injectors. Lowering the fuel pressure will cause the air/fuel mixture to go leaner but again limit you change to no more than 15%, if more correction is needed smaller fuel injectors may be needed. The fuel supply system must be able to supply enough volume and pressure to maintain the proper fuel

The Results of Proper Tuning

A properly tuned fuel and ignition system will allow your marine engine to perform up to its potential and will supply you with a better performing, more reliable and efficient running marine engine that will be a whole lot more enjoyable to use. Taking the time to properly tune your boat's fuel and ignition advance systems will not only allow you to have a more reliable marine engine with more drivable engine power, it can also help lower your engines fuel consumption. This properly tuned marine engine that has the correct air/fuel mixture and ignition advance curve will help you have a boat that runs great, has more power, uses less fuel and is free from the problems and this proper tuning may help avoid the engine damage that can result from incorrect ignition timing or overly lean air/fuel mixtures.

Race Engine Jetting

Excerpts from Circle Track Magazine, April 2004, by Henry Olsen

Jetting a carburetor is one of the few "black arts" in the automotive world that is still a mystery to most racers and tuners, most tuners look at the spark plug, the exhaust port and the first 6 inches of the header for proper "color" and make a guess at what jet size change is needed. One of the disadvantages of this method is that the header and spark plug can only indicate what the mixture was at the rpm and load condition at the time. The content of the engine's exhaust can show what the air/fuel mixture is and how efficiently the engine is burning the fuel. Races are often won or lost by getting more laps out of a tank of fuel than the competition, how efficiently the fuel is burned by the engine can be a major factor in the difference between winning and losing a race.

The proper tuning of a race engine can make the difference between being the winner or having never ending troubles while trying to just keep up with the competition. For most racers, one of the biggest mysteries is how do you jet the engine in order to obtain the correct air to fuel ratio necessary for your race engine to not only supply drivable horsepower under all race load demands but also while cruising during caution laps, having the air/fuel mixture correct for the engine's needs while you are cruising around the track at caution speeds is often ignored. If the air/fuel mixture is too rich for the engine while you are running at caution speeds, the engine may tend to load up and foul the spark plugs, while if the air/fuel mixture is too lean the engine may tend to run hot. Having a air/fuel mixture rich enough for all racing conditions will allow you to get all the horsepower out of the engine while getting as many laps as possible from a tank of fuel without overheating or doing any engine damage from having too lean of an air/fuel mixture, this is one of the many tricks it takes to beat the competition to the finish line. This may sound impossible, but the new advances in exhaust gas analysis technology have made it possible to "read" and/or record what the air/fuel mixture actually is under almost any driving condition. In the past exhaust gas analyzers have tended to be large and expensive, but we have been using one of new modern units from the PerformanceGas series of infrared exhaust gas analyzers from OTC/SPX; these units are not only compact and portable, but also affordable for a grass roots racer.

Most race carburetors sold today have a generic "tune-up" or jetting unless the carburetor is built for a specific engine package and fuel. Just adding mufflers or any header/exhaust system change such as adding an "H" pipe into the exhaust can cause the air/fuel mixture to change making it necessary to re-jet the carburetor. A carburetor not built and tuned for a specific engine, exhaust system, and fuel must supply an air/fuel mixture rich enough for a variety of engines. If the carburetor is supplying too lean of an air/fuel mixture, the engine will run sluggish, overheat or the lean mixture could cause engine damage. If the carburetor is supplying an air/fuel mixture that is too rich, the engine may tend to load up, foul the spark plugs, run sluggish and lack power.

Ignition Advance Curve

Before checking the air/fuel mixture, the ignition timing and advance curve must first be correct. Any distributor, performance replacement or original equipment, must have the mechanical and vacuum advance curves checked and then tailored to the engine and the fuel being used. (Note: MSD distributors come with a very conservative mechanical advance curve and included in the box are the bushings and springs to get the desired curve.)

Air / Fuel Mixture

A lean fuel mixture (too little fuel for the amount of air in the cylinder) can cause an engine to stumble or give a rough idle as well as to run too hot, overheat, and cause a lack of power as well as engine failure. A rich fuel mixture (too much fuel for the amount of air in the cylinder) can cause an engine to "load up" at idle, foul the spark plugs, and also lack power or run sluggish...An optional method of checking air fuel mixtures is by using a wide band oxygen sensor installed into the exhaust header, the wide band oxygen sensor is read using a digital air/fuel meter. The unit that I have had the best results from is available from Innovate Motorsports. This method looks at the oxygen/unburned combustibles in the engine's exhaust and then the unit supplies an air/fuel mixture reading; the readings are very accurate...

On Car Testing

After the basic engine condition and tune-up (fuel pressure, timing curve, etc) is confirmed to be correct, as well as checking to be sure there are no vacuum leaks, the next step is to determine what the air/fuel mixture is at idle through 3000rpm. If the cruise mixture is off, first change the jets in order to get the air/fuel mixture correct at the 2500-3000-cruise rpm range. Then check and set the idle mixture. If the air/fuel mixture is too lean at idle or part throttle and the idle mixture screws do not provide enough adjustment, the correction may involve enlarging the idle "jet". If the mixture is still lean at 1000 through 1800 rpm, the idle channel restriction, if used, may have to be slightly enlarged to allow more fuel to be delivered at part throttle.

This lean condition at part throttle condition will cause the engine to miss or stumble is due to the lean air/fuel mixture. This problem is very common on many carbs. (The notable exception is the Demon line of carburetors, which have used the PerformanceGas to do exhaust gas analysis along with dyno, track and drivability testing to establish the factory fuel curve that allows them to come with a stumble-free guarantee.) If the air/fuel mixture is too rich at idle and part throttle, the idle jet/restriction may be too big and may need to be replaced with a smaller one.

A carburetor has an accelerator pump, idle, main jets, and in most cases a power system that is designed to supply the correct air/fuel mixture for the engine's demands. An idle system will have an idle jet/restriction that must be changed to supply the desired fuel mixture for idle and off idle engine demands. For a carburetor that uses a power valve, the main jet size is what determines what air/fuel mixture is delivered to the engine at light load/cruise speeds (1500rpm and up). The power valve restriction (under the power valve) is the determining factor in what the air/fuel mixture the carburetor will supply when the power valve is open; a 6.5 inch power valve will be open and supplying the richer air/fuel mixture needed under high power demands anytime the vacuum is below its 6.5 opening point. A carburetor that uses metering rods in the primary jets such as a Quadrajet, will use the metering rods to change the air/fuel ratio for both the power and cruise mixture demands of the engine; the larger the metering rod diameter the leaner the air/fuel mixture will be. The accelerator pump adds fuel as the throttle valves are opened, tuning the accelerator pump squirter volume and duration it's tuning is mainly trial and error.

The Lambda meter method uses an extended range oxygen sensor to determine the fuel mixture by analyzing the unburned combustibles in the exhaust gas, a extended range oxygen sensor can read air/fuel mixtures as rich as 10 to 1 or on the lean side it can read air/fuel mixtures lf 19 to 1 or leaner (a standard oxygen sensor is only accurate at air/fuel mixtures of around 14.7 to 1)...The Innovate Motorsports Digital Air/Fuel Meter can allow you to sample and record the air/fuel mixture data at a rate of 12 samples per second over a period of up to 44 minutes, this data can allow you to tune the fuel mixture to the ideal air/fuel mixture curve that the infrared exhaust gas analyzer can help you establish.

Tuning at the track

When the engine is being used at a racetrack or anytime you are trying to get the very most from the engine, the air/fuel mixtures should be adjusted to correct for the ever changing air density. First, the baseline "tune-up" for the air/fuel mixtures must be set and correct for the conditions you have tested under, then the next step is fine-tuning for changes in the air density....

EFI CENTER

Tools for tuning Electonic Fuel Injection are expanding greatly. New laptop tuning solutions, chip tuners, etc. are coming out every day. These new tools allow you to modify injector duty cycles, target air/fuel ratios (and also timing, etc.). But regardless of what you're using to modify your fuel injection, YOU NEED TO KNOW WHAT'S HAPPENING. You need to measure the results of changes. You set the targets in your tuning solution, but you meaure the actual AFRs with the LM-1.

The steps are:

1) Measure and datalog with the LM-1.

2) View your logs on LogWorks.

3) Determine changes to be made with your tuning device.

4) Repeat the process until your vehicle is completely dialed in for your application.

In LogWorks, besides the graphing and overlay features, the Chart feature is especially useful for working with EFI-tuning devices. Simply configure the axis and step size to match your fuel map, and compare the actual AFRs to target AFRs. TUNING TIP: If you double click on any cell in the chart, you can input your target and LogWorks will calculate the multiplier for you.

Wideband EFI Tuning

SCCA Solo II Champion Tunes Honda S2000 & AEM ECU with Innovate Wideband

Innovate's wideband tuning tools (LM-1/LMA-3 or LC-1/DL-32 are two examples) allow you to optimize performance from an EFI system. The Innovate system captures information about how your car runs at wide-open-throttle, cruise, idle and transition – helping you optimize your engine's tune and improve your car's performance. Innovate's products log everything from basic RPM and Air/Fuel Ratio and Manifold Absolute Pressure (MAP) to more specialized parameters like Throttle Position and Intake Air Temperatures . After recording the data with the Innovate system, you can analyze this data, adjust a few calibrations in your EFI system's "fuel map" and then run the car again to check your results for performance gains. Less time spent guessing your way through fuel maps gives you more time for the track and a better chance at the trophies.

Most EFI systems – including the aftermarket "piggyback" or "black box" systems that operate on top of factory Engine Control Units (ECUs) – rely on a basic fuel map for metering fuel. The fuel map is either pre-installed or it requires the user to pull a fuel map calibration down from the EFI system manufacturer's Web site using their laptop and then upload the fuel map calibration to the EFI system's Engine Control Unit (ECU) or associated piggyback system. An EFI system's fuel map can be thought of as a three-dimensional (3D) map of X (Engine RPM), Y ( Load / Throttle Position ) and Z (Fuel Amount to Inject). A similar 3D map applies for spark advance by replacing axis Z's "Fuel Amount to Inject" with "Degrees of Spark Advance."

Example 3D EFI Map

The nice thing about using Innovate's LM-1 and LMA-3 to tune an EFI setup is the selection of sensors which feed the EFI system. Wires for the Throttle Position Sensor ( TPS ), RPM, Manifold Absolute Pressure ( MAP ), Intake Air Temp (IAT), Coolant Temp and Crankshaft Angle are used by EFI systems to calculate the proper time and amount of fuel to inject while the engine is running. This "pre-wiring" makes it convenient to attach the LMA-3 wires for channel input onto the wires that go into the EFI system's brain, giving you access to a wealth of data. The sensors for RPM, MAP , and TPS were tapped for the purposes of this discussion. NOTE: I tried to log knock data during these sessions. However, that signal is not a linear analog output so it turned out to be not useful for tuning.

1 Recording & Displaying Live Data: With your LM-1 and LMA-3 installed and tapped into the relevant sensors, it's time to take your car for a drive, capture some data and interpret the results. Capturing data is as easy as hitting the "Record" button once to start recording ("R" will flash on the LM-1's display) and once again to stop recording. Each recording is referred to as a "Session." You can record multiple sessions and up to 44 minutes of total recording time before you need to download the data to your laptop and free up the LM-1's onboard memory for additional recording. Using a laptop attached to the LM-1, you can also maximize the LogWorks Monitor display to see your car's Air/Fuel Ratio , RPM, Manifold Absolute Pressure ( MAP ), Throttle Position and Acceleration while the car is running – very helpful while you're tuning the idle in the garage or riding as a passenger while someone else drives the car.

LogWorks Virtual Gauges Showing Air/Fuel Ratio, TPS, MAP, Acceleration, etc.

2 Downloading & Viewing Recorded Data: Innovate makes it easy to pull recorded data down from the LM-1 to your laptop. With your laptop connected to the LM-1, open up the LogWorks Monitor software and click on the "File" drop-down menu, then highlight "Download LM-1 Log" to load your recorded data to your laptop. Once the download completes, you'll see a new window appear with a graphical representation of your session, similar to the screen shot below. You can toggle between multiple sessions using the "Session" drop-down menu of that new chart.

Screen Capture of new LogWorks session chart- Air/Fuel, RPM, MAP, Accel 1.jpg

It's a good habit to immediately save this newly downloaded data onto your laptop before you clear out the LM-1's memory storage of its old sessions. First click on "File" in that newly created graph's window, and then click on "Save As." Type a filename that includes something memorable about the session. An example is "1ClickLessFuel2000_2500RPM_AllMAPs.log" to denote taking one unit of fuel out from 2K-2.5K at all load levels. This practice helps you make sense of the log when you revisit it 3 months later. You can then clear out the LM-1's memory by going back to the LogWorks Monitor and clicking "File" and then "Reset LM-1 Log."

3 Baseline Practices: One of the first things tuners do before altering a fuel curve on any EFI car is to make a copy of the existing EFI system's map – assuming that the system allows you to copy the file to your laptop and later upload that file back into the ECU. This is helpful when you want to undo a change you've made to the fuel map. Now is also a good time to capture some baseline data about how the car runs before you make any adjustments to the original fuel map. Drive the car, record the data and download the data (and ECU fuel map file if possible) to your laptop – before making any changes. Then analyze the data, make your adjustments and drive the car again to determine if your changes resulted in the desired effect.

A good, safe practice is to baseline (and data log) a few runs on the dyno before making any changes to the fuel map (or spark map for that matter). With your baseline captured, you can compare your baseline run data against subsequent run data (done after adjustments).

4 Idle Tuning : Compared to the effort required to tune a carbureted car's idle circuit (which does double duty as the cruise circuit), tuning EFI systems for idle & cruise with a wideband is very simple. Most EFI systems apply the axes of RPM and Load ( MAP value) in order to arrive at an amount of fuel to inject. In the following diagram of an EFI system's fuel map, Engine RPM is the horizontal X axis and Load (MAP value) is the vertical Y axis. The numbers in each X-Y cell tell the EFI system how long to hold a fuel injector open for that RPM and MAP value.

EFI Fuel Mapping

For an example, say that you've captured some data and are reviewing it in the LogWorks interface shown in the following diagram. You click on LogWorks's gauge-like button in the upper left hand corner of the window, just below the drop-down menu for "Channels" to allow you to add a metrics box that shows the values of the data collected at that point in time. You can add as many metrics boxes as you like, and you can remove them just as easily by clicking on them again. The graph shows that at a 900 RPM idle the Air/Fuel Ratio is 13.5:1.

Idle Tune Air/Fuel Graph

If you want to lean it out just a tad (EFI guys are such perfectionists..) just open your EFI system's interface and make a few changes. With the interface open, locate the 900 RPM range for -12 to -10 PSI of MAP or Vacuum , highlight those cells as shown in the following diagram and then tap the minus key (-) to reduce the amount of fuel administered to your engine at idle. Less sophisticated EFI systems may require you to manually type in the values for these numbers, but even typing still beats the carbureted alternative if twisting mixture screws and replacing idle air bleeds.

Idle Change in ECU Software

Start the car up again and check the LogWorks gauges. The Air/Fuel Ratio has changed to 14.6:1 and the idle is now smoother at 860 RPM with about the same Vacuum . Some EFI interfaces even allow you to make your fuel mapping changes with the engine running, so you have the option of adjusting the fuel map while looking at the LM-1's Air/Fuel Ratio display.

EFI LogWorks Virtual Gauge Dials

Note: Most EFI systems will have a menu option that allows you to trigger an idle compensation system when the car's automatic transmission is in Drive but the car standing still. For those systems that don't, the previous tuning process can be used for cars with an automatic transmission. Remember to chock the wheels, engage the emergency brake and have a friend in the driver's seat pressing the brakes as you tune with the transmission in Drive. You can then sit in the passenger's seat to make the fuel map adjustments using the laptop.

5 Light Cruise Tuning: Next, you can measure and tweak (where necessary) the values in the EFI interface to the right of the cells you just changed. That section (1500 RPM and up, -11 to -12 PSI load ) is used for very light cruise conditions with very little load . Capture your data, make your changes to no more than two horizontal rows at a time, drive the car, capture more data, analyze and repeat as necessary until you feel like your cruise Air/Fuel Ratios are in the range you want them in and you haven't sacrificed drivability or safety. Again, look at your knock voltage readings and compare these against the baseline for any discrepancies. This process allows you to analyze whether your changes resulted in the Air/Fuel Ratios and drivability you sought in that range.

Save the Innovate data captured from the LM-1 (and the EFI system's current file if it allows you to -- using a similar filename convention) under a filename that makes sense to you for the changes you've done. You can at this point begin working your way upward 1 or 2 rows at a time on the EFI system's map to build out the cruise and transition section of the map. That process is described along with a couple of options for tuning the transition section near the end of this discussion.

6 Wide-Open-Throttle (WOT) Tuning: The same level of simplicity applies for tuning the car at wide-open throttle – it's just a different area of the map. Ideally, WOT tuning should be done at a dyno (to measure wheel horsepower and torque) and then the racetrack (compare quarter-mile ET and MPH as well as 60 foot times off the line). Tuning for WOT focuses on the upper part of the EFI system's fuel map shown earlier, where vacuum is closer to -1 or 0 (or positive values for boosted applications) and extends all the way from idle RPM through redline.

Most manufacturers will tune the EFI system to run between 11.5:1 and 12.7:1 in the high load , mid-upper RPM range for optimum power and engine reliability, while running mixtures near 13:1 at slightly lighter loads (-2 PSI). For even lighter loads, the EFI system switches into a "closed loop" feedback system that targets 14.7:1 for optimum fuel economy and emissions.

Looking at the high-load part of the map in the following table, look at the turquoise rows of Air/Fuel Ratio . This map is a LogWorks table taken from a Honda S2000 running on its factory fuel map. The table consists of many sessions collected across a wide range of throttle, RPM and load conditions.

Baseline Table

At the 0 and -1 PSI range (Wide Open Throttle), the Air/Fuel Ratio is between 11.8:1 and 12:1 from 1500 RPM up to 8250 RPM. However, the Air/Fuel Ratio seems to drop after 8250 RPM down into the 10:1 range – not conducive to maximum power. This is where Innovate's data logging can find you some horsepower by highlighting an opportunity to raise the Air/Fuel Ratio back into the 11s from 8250 to redline. The pink Air/Fuel Ratio line in the corresponding dyno run from this Honda confirms that the engine goes too rich after 8250 – the pink Air/Fuel Ratio line drops over a full point of Air/Fuel Ratio from 7500 RPM to 8500 RPM.

Baseline AFR Example

What's happening is that Honda deliberately adds extra fuel after 8400 RPM (the stock S2000's power peak) to drop the Air/Fuel Ratio down into the 10s. This artificially limits the power peak to 8400 RPM instead of the engine's true peak flow potential at 8800 RPM – where 8-12 more horsepower is available. Honda does this to reduce the likelihood of an average owner bumping into the fuel cutoff at 8900 RPM. Aftermarket "black boxes" like those from Greddy and Apex can run on top of the factory ECU, allowing an experienced tuner to use a wideband system like Innovate's LM-1 and tap that extra 12 horsepower by trimming the excess fuel injected between 8400 RPM and redline. This can be done by plugging your laptop into the black box's interface and editing the relevant RPM/ Load cells in a fuel map screen that's similar to what was described earlier in the Idle section. If you instead have a "stand-alone" aftermarket ECU in place of the factory ECU (as in the following diagram), you simply open up the interface and make your changes to the RPM/ Load cells there, and then go back and test for the resulting changes.

WOT Fuel Trim

It's safest to do this type of fine-tuning on a dyno first, paying careful attention to the Innovate LM-1's Air/Fuel Ratio readout and data logs in the areas of RPM and Load where you made the changes. In addition, pay close attention to the knock voltage you're logging in the LMA-3 and viewing in LogWorks. Compare your baseline logs against each set of changes so you can avoid harmful detonation.

7 Transition Tuning: You've now used your Innovate LM-1, LMA-3 and LogWorks software to check for knock and to fine-tune the idle and wide-open-throttle ranges of your car's EFI fuel map. All that's left is to "fill in the blanks" between idle and wide-open-throttle in the EFI system's fuel map. One of the easiest ways to measure and refine your EFI fuel maps in this "transition" area is to take your car to a dyno shop and make many dyno pulls, being sure to capture the data with your Innovate equipment. Although you may need to rent a few hours to thoroughly tackle all the ranges, a couple of hundred dollars is far less expensive than replacing an engine.

Concentrate on one load range at a time and use the Innovate LogWorks Instrument Panel of configurable dials to make each pull. Remember to hit "Record" on the LM-1 before you start this process. One approach is to base your pulls on TPS , making a full pull (from 1500 RPM or so up to redline or until the RPM plateaus) using only 10% throttle. You will have to actively watch the TPS dial and control your foot to ensure you keep it at 10% for the full pull. Then make another pull, this time at 20%, then 30% and so on until you make your last pull at 100% throttle.

Next, you can try capturing data based on making pulls referenced by engine load – trying to keep engine load ( MAP value or Vacuum ) as constant as possible through the pull or until the engine plateaus at an RPM level, starting at a load level that is a row or two above the idle load level you've set in the EFI system's fuel map. This practice is infrequently done, but can provide insight into stumbles or hiccups that aren't otherwise only show up in normal street driving.

After your final pull (of TPS and Load/MAP), download the data you recorded from the LM-1 to your laptop. Open up LogWorks's "View" drop-down menu, then click on "New Chart" option to bring up the Chart Settings box like the following graphic:

Viewing New Chart

Set your Horizontal axis to RPM and your Vertical axis to MAP and your Chart Content as LM1_O2 and click OK to bring up the table. Next, click on "Sessions" to select all of your sessions as content for the table you're building – this allows you to capture all the Air/Fuel Ratio s for the various dyno pulls you just ran and display them as a single table which you can very easily color code for easier viewing.

Enable color-coding by clicking on "Colors" and selecting the color scheme of your preference. Cells in the table automatically become color coded based on their numerical value. The color scheme in the following diagram is "Wobniar" (which is "Rainbow" spelled backwards) and intuitively has blue at the rich / cool side of the Air/Fuel Ratio spectrum and red as the lean / hot side.

EFI Transitions Viewed as Color-coded Table

Review the LogWorks table to examine cells that contain Air/Fuel Ratio s that don't make sense for the area of the fuel map that they are in. The previous table has a red cell in the lower right corner with a dangerously lean 22.39 Air/Fuel Ratio at 8500 RPM and 8.3 pounds of boost (this table is from an EFI car with a small turbo). The EFI system's fuel map needs to be checked and likely richened in that range. It also appears that there are some lean cells (over 15:1 Air/Fuel Ratio ) within the 4500 RPM – 5000 RPM range between -12 PSI and -3.18 PSI which need to have fuel added as well.

Remember to make one change at a time, measure the results, and repeat. Soon you will be "finding" horsepower and efficiency in all sorts of unexpected places!

Standalone ECU Tuning

Most modern standalone Engine Control Units can benefit from the use of a wideband Air/Fuel meter.A few of the basic applications are closed-loop EFI operation, tuning and setup, and narrow-band emulation.

Closed-loop EFI operation.In this application, the wideband controller (LM-1, etc.) controls the wideband oxygen sensor, and outputs a 0-5V signal that continuously informs the ECU what the measured air/fuel ratio is. The trick is to match the voltage-to-AFR correlation so that it is mapped correctly to the ECU. All Innovate wideband controllers have programmable analog outputs, so often it is as simple as determining what the ECU is "looking for," and programming the LM-1 to match it. Innovate digital wideband outputs are truly linear, and many older analog controllers are non-linear, so, in some cases, you'll need to reprogram the ECU's input table to match the Innovate output. Here's an example from a Electromotive Tech-3 ECU (link to Tech-3 App. Note):

Remember to ground the analog output to the same ground as the ECU to avoid ground offset issues. If you still see ground offset, you can shift the LC-1 or LM-1's output to compensate. NOTE: Some ECUs will operate in closed-loop mode only at cruise or idle (not at WOT), so check the specs on your ECU.

Basic Tuning. Another common application of tuning a standalone ECU involves utilizing Innovate datalogging capabilities (LM-1, DL-32, or LogWorks direct on a PC). Most ECUs ship with a base fuel map. This map is designed to get the vehicle running safely so that it can then be tuned to optimum. Accordingly, the base map is almost always far from perfect. Often it is way to rich, which means you're wasting fuel and losing horsepower.

The process here is to record a log of AFR and RPM (at least). With LogWorks, you can then graph and chart the actual AFRs, under real road conditions, at every load and RPM. With a chart like this:

You can make appropriate changes to your ECU's target fuel map, then repeat the process. By logging other key variables, such as throttle position- TPS, manifold absolute pressure- MAP, cylinder head temperature-CHT, and/or acceleration, you can further understand exactly what's going on with your engine, and dial in it in for maximum power, maximum efficiency, or the perfect balance.

Narrow-band emulation. In some cases, your ECU might operate best with a narrow-band oxygen sensor input. You can use the LM-1 to provide this also. The factory setting for output #1 is set to emulate the steep and narrow output curve of a stock narrow-band sensor. You can also shift this to "trick" an ECU into providing more horsepower under some conditions.

Piggy-back Fuel Controllers

Piggy-back fuel controllers are popular because they allow users to modify stock fuel injection without replacing the entire ECU. They operate in various ways. Some of them modify the injector duty cycle control signals as they travel from the ECU to the injectors. Others modify input data to the ECU (like MAF for example), effectively "tricking" the ECU into delivering more or less fuel at a given RPM. Regardless of how exactly the piggy-back works, you'll want to measure the results of any modifications you make to your fueling map.

Even if you can't tune the piggy-back (some are fixed and not user programmable), you'll want to make a log before and after you add the piggy-back. This helps you evaluate what exactly it's trying to do, and avoid dangerous lean conditions or wastefully rich conditions. If you can tune your piggy-back, use the LM-1 to carefully tune every cell of your fuel map.

Laptop Tuning

A new wave of laptop tuning tools have been coming to market that allow users to directly modify the fuel and timing maps of stock ECUs. These usually use the OBD-II port (On Board Diagnostics). Some of them, such as the EcuTEK system for Subaru WRXs, can directly read the LM-1's digital data stream and display AFR or lambda in the EcuTEK software. For all of them, you'll want to be carefully measuring air/fuel ratios (and other variables) while you're tuning.

Chip Tuning and Re-Flashing Devices

Handheld chip re-flashers have been around for a while. But recently, many of the most popular units are adding features that allow users to change key parameters like fueling curves and ignition timing.

The basic scenario is always the same: Use your LM-2 to log AFR, RPM, MAP, etc. before and after each change.

Squirt and Spark: How your ECU Works

There's a photo of me as a six-year old in my family's driveway. The look on my face is one of extreme concentration – I have a stethoscope in my ears and I'm hunched over the V12 that lived (and died) under the hood of my father's Jaguar. He is beside me, instructing me on how to adjust the four Zenith carburetors for balance by listening to the subtle changes in pitch at the air intake of each one. Didn't make the thing any more reliable, of course. But it made you feel you'd done something anyway.

Over the last 26 years I've figured out how most of an automobile works, and even got good enough at balancing the SUs on my own various MGs and early Jags that I can take care of it while my girlfriend pops into the loo at the filling station, which is about how often you have to do it

But then they went and invented fuel injection, and then engine management that unites fuel injection with engine ignition, and then they went and packed it in a little metal box. All the magic little set screws and plungers and orifices and weighted distributor advances and points gaps are set into a microchip, and you can hardly tell which part to hold the stethoscope to.

Unless you're one of the few who really understand how a modern Electronic Control Unit (ECU) works, it is probable that you subscribe to Arthur C. Clarke's notion that "any sufficiently advanced technology is indistinguishable from magic." If so, read on.

The Computers Are Just Smarter

Modern engine management is not rocket science. Its just doing the same thing that carburetors and distributors used to do, but better. We know (and the computer is programmed with) the ideal amount of fuel to mix with a certain amount of air at various engine speed and load levels. In The Olden Days the venturis and jets in your carburetor used to approximate this.

We and the computer also know when the plugs should spark to ignite this mixture for best burning at different speeds and loads. All of this was previously the job of your distributor and some kind of advance mechanism, and again it was approximated. Looking at how approximate the ignition and mixture used to be, it's remarkable that old cars ran at all. Certainly they ran very inefficiently.

Now, thanks to ECUs, we are in a halcyon era of powerful engines with flexible powerbands and relatively low emissions and high fuel efficiency. That Jag of my father's was the fastest sedan in the world when it was introduced. It put out 250hp from a 5.3 liter V12. Now you have 250hp in a 2005 Subaru Legacy with a 2.5 liter 4-banger. Internal combustion hasn't changed; the computers have taken over.

It's All About the Sensors

Electronic engine management is all about getting accurate information from the engine's environment and then sending out accurate signals to the control mechanisms of the engine. In a typical system you have the following input sensors:

1. throttle position of the accelerator

2. air temperature in the intake manifold

3. air pressure (or weight of the air) in the intake manifold

4. a measure of the residual oxygen in the exhaust manifold (the O2 sensor)

5. engine rpm

6. camshaft position

7. crankshaft position

8. engine load, usually as a function of manifold vacuum pressure

9. engine coolant temperature

10. about a zillion other things, like "knock" sensing, battery voltage, ambient air temperature, and whether Hoobastank is still on the Billboard top 40.

The computer simply takes all this data, compares it to data about optimum spark and fuel volumes for different conditions, and controls how much fuel to inject and when to fire the spark plugs.

Modern Mixture and Maps:

We know that there is an ideal air:fuel mixture ratio for each type of fuel - for gasoline this is 14.7 weight units of air to 1 weight unit of fuel, a so-called "stoichiometric" mixture. In principle, this is the mixture point at which all fuel injected will combust with all the gases in the ambient air. However the combustion is rarely perfect – an oxygen may never meet a hydrocarbon on the other side of a crowded cylinder of dancing vapours - so a somewhat leaner mixture (around 16:1) will ensure that excess air will gather up all of the hydrocarbons in the fuel and so will produce fewer emissions and better fuel efficiency. On the other hand a richer mixture will ensure that all the air that can be moved into the engine will combine with hydrocarbons in the fuel and so for maximum power you actually want this mixture to be richer - closer to 12:1. Since you're more concerned with power under hard acceleration and less concerned on the overrun (when you lift the throttle), the computer can target leaner and richer mixture ratios depending, literally, on how hard you stomp on the throttle.

Maintaining the ideal mixture is the function of your "fuel map" and it determines how much fuel the ECU will inject during each cycle of the engine. Essentially the map is a compromise to give you power when you want it, keep emissions as low as possible, and all the time keep the mixture within safe parameters to avoid damage to the engine.

How much Air?

Before it can determine how much fuel to squirt in, the main challenge for the ECU is to know what weight of air is in the intake manifold and getting sucked (normally aspirated) or pushed (turbo or supercharged) through the intake valve. Modern ECUs measure this in one of two ways: either by taking the pressure and temperature of the air in the manifold and calculating Manifold Absolute Pressure (MAP), or by measuring the weight of the air (Mass Air Flow or MAF) as it moves into the intake past a heated wire filament across which the ECU can measure electrical resistance. Older systems used other means, including various flaps and pulleys (I'm not kidding) to measure airflow. Now most production cars use MAF, although I use MAP in my rally car and some manufacturers, including Subaru, are moving back towards this.

How Much Fuel?

The main mixture job of the ECU is to control the injectors. Fuel injectors are little spray nozzles that can be snapped open and shut by an electrical charge: the amount of time they're open, combined with the pressure of the fuel coming in and the size of the injector, determines how much fuel will be injected. In "multi-point" fuel injection systems there's an injector for each cylinder, while in more basic systems ("Throttle Body Injection") there's just one for the whole intake.

So what determines how long the injectors stay open? The ECU senses the weight of the air, the rpm of the engine, and compares this to the data "map" it contains about ideal mixture for each load-rpm condition (see "base fuel delivery" graph). It then decides how long to open the injectors for and sends an electrical signal to them for the right amount of time. At idle the injectors open for just a millisecond – long enough to keep the engine ticking and no more. But mash the throttle and they go towards the maximum "duty cycle" – theoretically they could stay open 100% of the time but generally are engineered to give full throttle by being open about 80% of the time – that is, 80% of the time that it takes the crankshaft to go around twice. Thus is mixture in the modern engine determined.

When to Spark?

As engine speed increases, you need to ignite the mixture in the combustion chamber progressively earlier to get most efficient ignition. Note that the "explosion" in each cylinder is really a very fast fire and that the "fire front" moves through the mixture until burning is complete. The earlier you can spark the mixture, the more power you'll get as there will be more time to burn all the vapour before the exhaust valve opens. But if you fire the spark too early, you will end up with the explosion completing too soon and you get an uneven leading edge to the burn – effectively a separate explosion - called a "detonation." This may allow a "hot spot" of the explosion to hit the top of the piston (normally it is protected by a barrier of other gases at the edge of the explosion), and this is what a "knock" in the engine is. All engines knock somewhat, actually, but if you don't keep it within an acceptable level you will burn a hole right through the piston. Don't ask me how I know.

Higher octane fuel, by the way, burns more consistently at the leading edge, which is why for most race applications we use fuels with an octane above 100 while you might use 87 in your street car, and why we can advance the timing and run higher compression in the race cars. Lead additives in the fuel prevent detonation, but as you know this is mildly toxic and so we don't use it any more. Of course blowing engines is mildly toxic, too.

So for ignition, you have a second "map" that determines when to fire the spark plugs, based again on engine rpm and load (see "base ignition timing" map). In many four cylinder engines you have two coil packs and each has two plugs attached to it – when the ECU determines it's the right time to fire one of the plugs it sends current to one of the coil packs and two plugs actually fire, although one is redundant and has no fuel to ignite (creating a "waste spark"). It's just cheaper and more reliable than having four individual coils or (horror!) a distributor.

Other Stuff:

So the fuel delivery and spark timing maps are the real essence of what the ECU is doing for you all the time. Thousands of times per second the ECU is calculating how much fuel to deliver and when to spark.

But that's not all. For example, it knows when the engine is cold and it delivers more fuel and adjusts the spark for smooth running until the engine warms up. It also knows if the engine gets too hot and it can drop into "limp mode" to get you home by cooling the explosions with a richer mixture and later spark.

It also has two other very important sensors that adjust the fuel and spark maps constantly. The first is the "oxygen sensor" in the exhaust manifold, which sends information about how much oxygen is left over after the explosions in the engine. The computer takes this data and constantly adjusts the fuel mixture to keep this near maximum efficiency (14.7:1) or maximum power (12:1) depending on settings. Running in this mode is known as "closed loop" as the ECU is constantly adjusting itself to get the desired exhaust. There are a couple of interesting consequences to this: it self-adjusts for different qualities of fuel, and (this is cool) it even learns to change the entire fuel map for the car as the engine wears over the life of the car. But the sensor itself is a rather specialized device and deteriorates over time, which is why the #1 emissions-test failure is a faulty oxygen sensor. Now you know.

The second common and important feedback sensor is a little microphone attached to the engine block that can sense "knocking" or detonation from the cylinders, allowing the computer to adjust the timing backward (later) to prevent damage to the pistons. A few knocks per 100 cycles will be OK. More is bad. Note that there can be problems associated with this sensor: the Mitsubishi 4G63 engines especially in Galant VR4s and Talons can be afflicted with a "phantom knock" even when the engine is running properly but goes into limp mode anyway, sapping power. Basically the microphone is picking up noise from somewhere else in the engine and sending it to the computer as a knock; many Mitsu people find that the valve lifters are the source of the noise. Similarly, in a rally car we have constant barrage of noise from rocks on the chassis and this can be picked up. As a result, I don't have a knock sensor.

Opening Pandora's Box:

So now you have a dangerous amount of knowledge and want to completely remap your Honda, right? Be careful. It's not rocket science, but it's not model rocketry either. Still, there is good reason to start fooling around. Modern cars are mapped to provide a reasonable tradeoff between fuel efficiency, emissions, and power. If you care more about one of these things you can tune the engine more aggressively towards that. I'm going out on a limb and guessing you want more power, right?

Basically your typical aftermarket remapping is about richening the mixture throughout the range towards maximum power (12:1) and away from maximum efficiency (14.7:1). You'll use more fuel, but get more grins. Also you'll get more emissions, not just because of the residual hydrocarbons in the exhaust, but because this will cool the exhaust and catalytic converters are designed to operate within a very narrow temperature window.

In terms of timing, the factory settings are very conservative, presuming you will run rotten fuel sometimes and that you want the engine to last for a while. If you're committed to running higher-octane fuel all the time and putting your engine at some risk of detonation, then you can advance the timing a bit and get more power.

How much more power, and how to get it?

Basically you have four options if you start playing with your ECU: 1. replace or "reflash" the memory chip that contains your fuel and timing maps. Normally you remove the ECU and send it away for this to be done; some devices now exist for you to do this on your own. ($50 to $800) 2. Put a "piggyback" additional board between the ECU and the sensors/injectors/coils that modifies the signals to and fro and allows you to effectively remap the engine, although you're limited by some of the original ECU's parameters. ($500 to $1200). Note that you can reflash the chip at the same time to open the limiting parameters, and I've seen 450hp Evos with this system. 3. Replace the entire board in your original ECU case and plug the factory wiring harness directly into it (a "plug-and-play" board) that offers full programmability. This is what I use in my rally car. (to approx. $2000) Or 4. replace the ECU with an aftermarket one that will require you to significantly rewire your car (to approx. $2000).

But the real challenge is not how to get programmability. It's what to program. Either you should rely on another tuner's wisdom and use their maps (Dinan, Cobb, Vishnu, etc.), or you need to get on a dyno and burn up some tanks of fuel to find out what mixtures and timings really produce the most power and torque for your particular engine on your particular fuel. It's a time-consuming and precision process and requires some experience. The bottom line is what you see on the horsepower and torque curves from the dyno.

There's another device you need, though, and I'm happy to report that it is now available to the common man. You need to get information from that oxygen sensor in the exhaust so that you can monitor mixture while you're tuning for power – too lean and you'll start blowing engines; too rich and you'll lose power (and, at the extreme, start blowing engines). Although you can get little LED readouts for your dash that appear to tell you about mixture they're not accurate enough and you really need a digital device that can log the mixture against load, rpm, throttle position, etc. Until recently, the main options were air-fuel meters available from MoTEC ($2200US) or Autronic ($1800US) which is a serious investment.

But there's a new product on the market that I've used and I love: Innovate Motorsports (www.innovatemotorsports.com) now makes an affordable fully digital and data-logging air-fuel meter that retails for $349US. I've used it to tune my Evo already and I find it perfect for the job. Install the sensor in your exhaust and power the device up and you are already looking at the A/F ratio (or "lambda"). Wire in up to five additional inputs and you can watch them on screen as you tune, or log them for up to 44 minutes in the device itself and download it later (great for road tests). Also you can take the analog output signal and feed it to your ECU, as I've done, so that you can see A/F ratio against all the other engine parameters you can monitor by hooking up directly to the ECU. I really like this device, and won't tune without it now. I recommend it strongly. It won the SEMA award for "Best New Product – Performance and Racing" this spring and I can see why.

Conclusions:

The bottom line is this: ECUs use a group of sensors to gather information about engine running conditions and use two maps – one for fuel and one for spark – to control how long to open the injectors and when to fire the spark. Playing with these yourself is entirely possible, although it requires some knowledge to get the best out of it. Note that any remapping is likely to cause you to fail emissions tests and void the warranty of your car, so you've been warned. But who's thinking about that when you're putting out 450hp from 2 liters, right? Best of all: no stethoscope required.

Recommended Reading: Forbes Aird, Bosch Fuel Injection Systems, HP Books 2001.