The Edelbrock #608915 Performer RPM cylinder heads are designed for 1955-86 Small-Block Chevy applications. The Edelbrock #608915 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: • EQUIPPED WITH SPRINGS FOR USE IN MECHANICAL FLAT TAPPET AND HYDRAULIC ROLLER CAMSHAFT APPLICATIONS • Match with Edelbrock head gasket sets. • To use stock rockers on small-block Chevy heads, .100" longer than stock pushrods are required. Edelbrock pushrods #9629 are recommended. • Use Head Bolt Kits for easy installation. Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat. • S/B Chevy heads may not be used on engines with less than 4" bore (262, 265, 283, 305, 307 c.i.d.) except with cams having less than .450" valve lift.