"A standard small-block Chevy head suffers from pushrod pinch and valve location in the bore. Compared to a 23-degree head with standard location intake ports and rocker arm and pushrod layout, an 18-degree head will make substantially more power. Most 18-degree SBC heads have been stuck in the 330- to 340-cfm range for many years, and we have yet to see anything go above that. If a 23-degree head has the valve relocated closer to the center of the bore and a shaft rocker is employed to eliminate the pushrod pinch, then the difference in power production between the two is much closer. The advantages of a 23-degree head are piston, rocker, and intake availability. When you make the jump to a raised-runner 23-degree head with relocated valve centerline and shaft rockers, you have to get custom pistons, custom rockers, and an 18-degree type of intake manifold. In this case it would make more sense to simply run an 18-degree head unless class rules dictate that a 23-degree head must be used. We chose to develop our CNC-machined 230cc Super 23 heads well over two years ago to support the big-cubic-inch SBC market. We did not want to make customers buy special rocker arms, intake manifolds, and headers in order to realize huge gains in airflow. This head moves enough air to support 650-plus hp out of the box, and does this with conventional valve and port locations."