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.