The Edelbrock #60049 Performer RPM Super Stock Cylinder Heads are designed for 400, 430 and 455 c.i.d. Buick engines. This cylinder head includes adjustable rocker stud and guide plate set-up for use with small-block Chevy style adjustable 1.6:1 ratio rockers. The large 68cc combustion chambers produce 9.2:1 compression ratio with stock pistons. 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 NOTE: • 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: 3/8" • Pushrod diameter: 3/8" (width of slot in guide plate).