Engine Pro Hi-Zinc is a must have for flat tappet applications. Mix with oil at each change.In an effort to make catalytic converters in modern cars last longer, U.S. government regulations have forced the engine oil companies to seriously reduce the level of anti-wear protection additive in current API approved street oils. This has caused an alarming increase in cam and lifter failures in engines with flat tappets and flat tappet camshafts.Engine Pro now offers anti-friction and engine wear products designed for all vehicles using flat tappet camshafts.  HI-ZINC ENGINE PROTECTOR  (40-1900) For classic and other cars with flat tappet cams without OBD, zinc and phosphorus  (ZDDP) must be in the oil in a higher concentration than it is in current API oils,  especially during the crucial break-in period.  ENGINE PRO HI-ZINC ENGINE PROTECTOR  adds back the ZDDP that these engines  need to help prevent premature wear  and eventual failure. • Provides protection against camshaft, lifter and valve train damage • Dramatically reduces friction and engine wear • Prevents scuffing and galling • For both gas and diesel engines • For use with all petroleum and synthetic motor oils • Contains high concentration of zinc and phosphorus (ZDDP) • Designed to allow piston rings to seat properly when used during engine break-in • Available in 4 oz. bottles