Replaces the OEM valves & valve springs and can be installed using the OEM retainers, bases and valve seats Offers increased durability and easily extends 3 times the lifespan of the OEM Titanium valves Due to the extra weight of the steel a heavier valve spring must be used! ProX has developed the Steel Intake and Exhaust Valve & Spring Kits, containing a set of steel intake or exhaust valves plus a set of specially designed stronger valve springs Nitrided valves offer high microhardness while supersmooth surface finish reduces friction between stem and guide Spring are made from premium Chrome Vanadium Steel for higher performance and durability under high RPM