These heads are based on the popular RPM series of cylinder heads for S/B Chevy and Ford. They are exclusively designed for the SCCA American Sedan Series Class and feature smaller intake valves, exhaust valves and non-interlocking exhaust seats. Manufactured from A356 aluminum and heat treated to T6 spec for superior quality and supplied with Manganese bronze valve guides, Heli-Coil® inserts in the exhaust and rocker stud holes. Bare heads are supplied with reamed and semi-finished valve stem guides and no valve job. Final guide sizing and valve seat finishing must be completed before installation. Engraved with the SCCA logo on both ends to help verify legality. These new cylinder heads have been approved by the SCCA for American Sedan Class competition.