The Edelbrock part No. 79559 Big Block Chevy E-CNC 355 cylinder head is the ultimate in performance. This cylinder head is fully CNC ported for maximum horsepower and torque, making them ideal for high-performance's 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: - This cylinder head delivers maximum horsepower and torque in high Performance's street and light duty racing applications - Full CNC porting of the combustion chambers, intake & exhaust runners.