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. The ProX kit just replaces the OEM valves & valve springs and can be installed using the OEM retainers, bases and valve seats. Steel Valve & Spring Kit Features: Steel valves for increased durability and less wear under extreme conditions, Nitrided valves offer high microhardness while super smooth surface finish reduces friction between stem and guide, Special stronger valve springs deal with the extra weight of the steel valves, Spring are made from premium Chrome Vanadium Steel for higher performance and durability under high RPM, Fully rebuildable with OEM retainers, bases and seals without the need of any further engine modifications, Comes as complete package for quick, easy and cost-efficient replacement