The Edelbrock High-Performance Performer RPM Cylinder Heads are ideal for high-performance street, drag racing and marine applications. These cylinder heads offer dyno-proven increases in horsepower, throttle response, and torque throughout the RPM range. They have top quality features like threaded inserts for rocker studs and exhaust manifold bolt holes for durability and superior strength, and manganese-bronze valve guides. The intake and exhaust runners are CNC-profiled for superior flow and performance. These heads made over 500 plus hp at 6, 500 RPM (+30 hp more than ported factory heads) and 525 plus foot per pounds of torque at 4, 500 RPM with the Performer RPM Total Power Package. The 75cc combustion chamber is available to offer a variety of compression ratio choices with engines of various sizes. They accept factory exhaust, aftermarket headers and factory valve train components and require the use of 3/8" diameter pushrods.