The Edelbrock #60517 Performer RPM NHRA Stock/Super Stock cylinder heads are designed for 1965-76 Oldsmobile 400, 425 &455 c.i.d. V8 applications. The Edelbrock #60517 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. For use on pre-pollution controlled vehicles only.INSTALLATION NOTES: • 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. • Head bolt holes drilled for stock 7/16" bolts, but can be easily modified for 1/2" bolts or studs by drilling the 1/2" counter bore. • Aftermarket 7/16"-stud rocker arms and 3/8" hardened pushrods required. • Will fit 350-403 Olds with Edelbrock manifold #7111 only (port matching required). Match with Edelbrock head gasket sets. • Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat. • Deck thickness: 5/8" • Rocker stud diameter: 7/16" • Pushrod diameter: 3/8" (width of slot in guide plate). • Cylinder Heads designed for high-performance non-emission 1965-76 Olds 400, 425 and 455 c.i.d. V8's • Heart shaped chamber for a more efficient burn, outstanding horsepower and torque • Valvetrain has been upgraded from the factory pedestal-mount system to an ARP 7/16" screw-in stud and 3/8" pushrod-slot guide plate for increased valvetrain stability • #60517 is not port matched or bowl blended and is NHRA-accepted for Super Stock (except 1968-1969 W-30) only.