The Edelbrock Victor CNC 11 6-Bolt Cylinder Heads for GM LS3 68cc Individual #77661 is specifically designed for high horsepower naturally aspirated and boosted applications. Edelbrock Victor CNC 11 6-Bolt Cylinder Heads for GM LS3 engines utilize the popular LS 6-bolt design making them compatible with the GM LSX block and all aftermarket iron or aluminum 6-bolt per cylinder LS race blocks. The 6-bolt design offers increased clamping capacity over the standard factory 4-bolt configuration and greatly improves head gasket sealing making them ideal for high compression naturally aspirated engines and high boost applications. These heads are manufactured with premium materials and machined to the industry's tightest tolerances. Features include an 11 valve angle copper infiltrated powder metal valve seats and fully CNC-machined ports for maximum airflow. The CNC-machined runners and chambers as well as the rolled 11 valve angle increase overall flow capability while the revised water jacket design enhances thermal conductivity and tunability. The premium manganese bronze valve guides withstand long wear with emphasis placed on holding precision tolerances on valve seat concentricity allowing the valves to seal securely which eliminates leak down and increases cylinder pressure during engine operation. Finally the .700 thick deck and reinforced rocker rails make these cylinder heads ideal for high horsepower applications. Edelbrock #77661 is assembled with premium COMP Cams valve train components including .700 lift dual springs tool steel retainers stainless steel intake/Inconel exhaust valves and premium valve seals – all inspected and assembled by qualified Edelbrock technicians.