Made for the 1965-73 389-455 Pontiac V8 engines. These heads are patterned after the 1969-70 Ram Air IV heads. The “Performer” RPM heads provide outstanding horsepower along with excellent low-speed torque and throttle response. Because of the high-flow D-Port exhaust ports, Ram Air IV headers or exhaust manifolds must be used. The complete heads are assembled with stainless steel, one-piece swirl-polished 2.11" intake and 1.66" exhaust valves with under-cut stems to promote better flow for more power. Includes 2-ring positive oil control seals, rocker studs and guideplates, valve springs, steel retainers and keepers. Heads include bronze guides, hardened valve seats and the deck surface is 5/8" thick. Part# G221435—Head bolt set for part# G980036. For some time now, this specific cylinder head has featured a new head-bolt boss height. This improves performance under super high-compression, supercharger or nitrous applications. This also simplifies the bolt kit: Head bolts of three different lengths are required as opposed to the six different lengths required with the old head bolt kit.