The Edelbrock #60589 Performer RPM 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. The Edelbrock #60589 Performer RPM heads with the 72cc combustion chamber are for higher compression engines. Performer RPM heads are perfect for street performance, daily drivers, street rods and muscle cars where seat-of-the-pants performance is needed. These cylinder heads deliver great throttle response and power from 1500 to 6500 rpm. They also feature the highest quality intake and exhaust valves and valve springs.INSTALLATION NOTE: • 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. • These heads require Ram Air IV (round port) style exhaust manifolds or headers • Edelbrock head bolt kit #8549 • Deck thickness: 5/8" • Rocker stud diameter: 7/16" • Pushrod diameter: 5/16" (width of slot in guide plate).