The Edelbrock #61555 Performer RPM Marine-Duty cylinder head is designed for use with Rectangular Port Big-Block Chevy Marine applications. The Edelbrock #61555 Performer RPM head is perfect for street performance, daily drivers, street rods and muscle cars where seat-of-the-pants performance is needed. This cylinder head delivers great throttle response and power from 1500 to 6500 rpm. They also feature the highest quality intake and exhaust valves and valve springs. For use on pre-pollution controlled vehicles only.