The Edelbrock Performer RPM Cylinder Heads offer improved performance throughout the RPM range for great throttle response and top-end horsepower with excellent low speed torque. Top quality features include threaded inserts in rocker studs and exhaust bolt holes for superior strength and durability, and manganese-bronze valve guides. This 72cc combustion chamber is designed for higher compression engines. The complete heads include stainless steel 2. 11 intake and 1. 66 exhaust valves, rocker studs, guide plates, valve springs, steel retainers and keepers. All factory accessory bosses are included for bolt-on convenience.