The Edelbrock part # 79559 Big Block Chevy E-CNC 355 cylinder head is the the ultimate in performance. These cylinder heads are fully CNC ported for maximum horsepower and torque, making them ideal for high-performance street and light duty racing applications. They also feature high-quality lightweight valve springs and heavy duty hardware for maximum lift and maintain the stock exhaust port location. E-CNC 355 FOR B/B CHEVY (RECTANGLE PORT) FEATURES: - These cylinder heads deliver maximum horsepower and torque in high performance street and light duty racing applications - Full CNC porting of the combustion chambers, intake & exhaust runners; improving air-flow & overall performance potential - These heads have a 24.5° x 4.4° intake valve angle, 15.5° x 4.2° exhaust valve angle and exhaust ports that have been raised 0.125" but are still in the stock location - Spark plug angles have been modified to produce a smooth flame front for increased fuel efficiency & maximum power - combustion chamber size of 118cc - Equipped with valve springs for use in hydraulic flat tappet applications INSTALLATION NOTE: Match with Edelbrock head gasket sets . Recommended spark plugs are Champion RC12YC or equivalent 14mm x 3/4" reach with flat gasket seat.