The Small-block Chevy cylinder head is designed for 1987-95 Throttle Body Injected (T.B.I.) and Tuned Port Injected (T.P.I.) 5.7L S/B Chevy engines originally equipped with centerbolt valve covers. Performer centerbolt cylinder heads are 50-state street legal and accept factory centerbolt valve covers. The intake bolt pattern utilizes the 1987-95, 73° angle on the two center bolts. Will maintain stock compression ratio when used with the recommended head gasket. The Corvette centerbolt cylinder head is designed for 1986-91 Tuned Port Injected (T.P.I) 5.7L small-block Chevy Corvette engines originally equipped with centerbolt valve covers. Performer centerbolt cylinder heads are 50-state street legal and accept factory centerbolt valve covers. The intake bolt pattern utilizes the 1986-91 (straight) 90° angle on all bolts. Spark plugs are angled like stock O.E. heads. INSTALLATION NOTE: Match with Edelbrock head gasket sets. Bare heads will have valve guides and seats installed, but will require final sizing and a valve job to match the valves you will be using. Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat. Bare heads will have valve guides and seats installed, but will require final sizing and a valve job to match the valves you will be using. Edelbrock pushrods #9632 are recommended. Requires hardened pushrods. Pedestal mount rockers. When using hot air choke Q-Jet carbs, choke kit #1932 is required. Intended for use on small-bore (3.736" - 4.00") 265, 283, 305 & 307 engines. Deck thickness: 9/16", rocker stud diameter: 3/8", pushrod diameter: 5/16" (width of slot in guide plate).