The Edelbrock 60509 Performer RPM cylinder head is designed for outstanding performance gains in 1962 - 79 389 - 455 c.i.d. Pontiac engines. They are patterned after the 1969 - 70 Ram Air IV Pontiac cylinder head. The Edelbrock 60509 Performer RPM head with the 72cc combustion chamber are for higher compression engines. Performer RPM 60509 is semi - machined and must be finished by a professional cylinder head porter. They include valve guides and seats installed with no intake pushrod holes.