The Edelbrock Performer RPM Cylinder Heads are 50-state street legal and 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. The 87cc combustion chambers are designed to maximize performance with low-octane fuel and streetable compression ratios such as 9. 5: 1. The 72cc version is for higher compression engines. They have a 5/8" deck for durability and head gasket retention.