The Edelbrock #60887 Performer RPM Bare NHRA Stock/Super Stock cylinder heads are designed for 1955-86 Small-Block Chevy applications. These cylinder heads deliver great throttle response and power from 1500 to 6500 rpm. Cast and heat treated at the Edelbrock Foundry and machined at Edelbrock's manufacturing facility in the USA, Edelbrock heads are the best in quality and performance. All Edelbrock Cylinder Heads are designed from scratch using the latest in computer technology by our own highly skilled engineer's. Using highly efficient ports and state-of-the-art combustion chamber shapes, Edelbrock cylinder heads offer improved performance throughout the rpm range for great throttle response and top-end horsepower. Top-quality features include threaded inserts in rocker stud and exhaust bolt holes for superior strength and durability, and manganese-bronze valve guides with ductile iron valve seats. These are features that some other companies don't include!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. • 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.