The Edelbrock #60037 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. These cylinder heads deliver great throttle response and power from 1500 to 6500 rpm.INSTALLATION NOTE: • Match with Edelbrock head gasket sets. • 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. • 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).