Air flow makes horsepower. The more cubic feet per minute (cfm) of air that flows through the intake ports and into the combustion chambers, the more horsepower the engine makes.
A larger carburetor or throttle body, bigger valves, a high-lift, long-duration camshaft, three-angle valve job and exhaust headers are all performance enhancements that increase airflow for more power. Add a turbocharger or supercharger, and even more air is forced through the engine. But, bolt-ons can accomplish only so much. To realize the utmost performance potential from a given combination of cubic inches and mechanical modifications, you also have to optimize the ports in the cylinder heads and match the ports to the runners in the intake manifold.
There are two ways to port and match cylinder heads: the right way and the wrong way. The right way is to refine the flow characteristics of the head and manifold so as much air as possible enters the cylinders at the engine