These cylinder heads are 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. Performer heads #60579/#60575 are 50-state emissions legal for 1965-79 vehicles. They feature 87cc combustion chambers designed to maximize performance while using less expensive, low-octane fuel with a streetable 9.5:1 compression ratio. Our Performer RPM heads with the 72cc combustion chamber are for higher compression engines. Performer RPM #60509 is semi-machined and must be finished by a professional head porter. They includes valve guides and seats installed with no intake pushrod holes. Performer RPM #60587 is not port matched or bowl blended and is NHRA accepted for Stock & Super Stock. Edelbrock Performer RPM Cylinder Head 60587 Chamber Size 72cc - Bare - Single - Pontiac RA IV - NHRA Legal - Not For Sale Or Use On Pollution Controlled Motor VehiclesOut-of-the-Box Bolt-On PerformanceValves Promote Excellent Flow For Streetable PowerThicker Deck Surfaces than Other BrandsPit Stop USAoffers Edelbrock Performer RPM Cylinder Head 60587 at low everyday prices. Be sure to check out all of the products from Edelbrock including Edelbrock Engine Parts and Accessories, Edelbrock Cylinder Heads, Edelbrock Aluminum Cylinder Heads - Pontiac.