Integrated Engineering Ferrea Valve Spring & Retainer KitWhen building a performance cylinder head for higher power output from larger turbochargers the power band is increased and moved higher into the RPM band. This puts increased stress on the valves resulting in valve float from the weak factory valve springs. Rev higher and increase your RPMs safely by adding Ferrea's spring retainer kit to your engine build. Heavy duty valve springs and spring rates keep the valves operating correctly under high load