The Edelbrock 608979 small block Chevy Performer RPM cylinder heads are designed exclusively for the SCCA American Sedan Series Class. To comply with class rules, there is no blending work in the intake entries, exhaust exits or bowl area of the intake or exhaust. Bare cylinder heads will require final sizing of the valve guides and a proper valve job prior to the installation of valves. These heads are engraved with a SCCA approved logo and legal for American Sedan Class. For additional information, please refer to the SCCA rule book. 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. To use stock rockers on small-block Chevy heads, .100" longer than stock pushrods are required. Edelbrock pushrods #9629 recommended. Use Head Bolt Kits for easy installation. 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: 9/16", rocker stud diameter: 3/8", pushrod diameter: 5/16" (width of slot in guide plate).