The Edelbrock part # 61209 Small Block Chevy E-CNC 225 cylinder heads offer the ultimate performance. These cylinder heads are fully CNC ported for maximum horsepower and torque, making them ideal for high-performance street and racing applications. They also feature high-quality lightweight valve springs and heavy duty hardware for maximum lift. E-CNC S/B CHEVY FEATURES: - Features fully CNC machined intake ports, combustion chambers and exhaust ports for improved performance - Maintains the stock 23° valve angle and intake flange bolt pattern for use with 1986 and earlier intake manifolds - Delivers up to 30-60 horsepower over Performer RPM Cylinder Heads - #61205 & #61209 features 7/16" studs and angled spark plugs - Ideal for high performance street and racing applications INSTALLATION NOTE: Match with Edelbrock head gasket sets. Bare heads will have valve guides and seats installed, but will require final sizing and a valve job to match the valves you will be using. Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat.