JUN manufactures aftermarket performance parts and engines for Japanese cars. They make parts such as piston kits, stroker kits, valves and Plenums. The parts they make are designed to upgrade the performance over standard OEM parts.
There are two types of valve guides from JUN. One is a strengthening part made of phosphor bronze which is suitable for race engines. The other is the valve guide made of cast iron which is the same as stock specification.
On race engines, the heat and mechanical load by high rotation will be produced much more than stock and the stock valve guide can't handle it. JUN Racing Valve Guide is much more durable and features superior heat conduction by using raw material, phosphorus-bronze. This therefore will avoid any damage from high rotation of race engine.
For cast iron valve guides, not only improving their quality, but also the price was kept lower than factory stock valve guides which have been becoming rather expensive lately. Recommended to be used when the cylinder head is overhauled.