The Edelbrock Performer RPM Aluminum Cylinder Heads feature threaded inserts in the rocker studs and exhaust manifold bolt holes for superior strength and durability. These cylinder heads offer dyno-proven increases in horsepower, throttle response, and torque throughout the RPM range. These direct bolt-on heads deliver maximum performance in the 1, 500-6, 500 RPM range for high performance. They offer improved power throughout the RPM range for greater throttle response and top-end horsepower. They have high flow 2. 02 intake valves for use with pistons notched for valve clearance and 0. 60 exhaust valve. They have the top quality features like threaded inserts for rocker studs and exhaust manifold bolt holes for durability and superior strength, and manganese-bronze valve guides.