The Edelbrock 602479 small block Ford Performer RPM cylinder heads are designed exclusively for the SCCA American Sedan Series Class. They feature non-interlocking valve seats to accomodate 1.94" intake, 1.55" exhaust valve sizes. To comply with class rules, there is no blending work in the intake entries, exhaust exits or bowl area of the intake or exhaust. The casting is manufactured of A356 aluminum and heat treated to T6 spec for superior quality. All heads include manganese-bronze valve guides, one-piece stainless steel valves with hardened tips, ductile iron valve seats and Heli-Coil® threaded inserts in the exhaust and rocker stud holes. Bare heads will require final sizing of the valve guides and proper valve job prior to the installation of valves. All Edelbrock SCCA RPM heads are engraved with the SCCA approved logo and are legal for the American Sedan Class. For additional information, please refer to the SCCA rule book. INSTALLATION NOTE: Hardened pushrods required, use Edelbrock #9632 (flat tappet only). Will not accept rail rockers. 289-302 V8s require Head Bolt Bushings #9680 and either Head Bolt Kit #8552 (7/16") or stock head bolts. 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. This head does not include valve springs due to the wide variety of camshafts used in competition. Please consult your camshaft manufacturer for appropriate valve spring selection. Deck thickness: 5/8", rocker stud diameter: 3/8", pushrod diameter: 5/16" (width of slot in guide plate).