Import Killer Part 2: 925 hp From 454 Ci Engine - Tech

The intake-to-exhaust flow ratio of the AFR heads is also much better than the stock heads. For example, at 0.600-inch valve lift, the AFR exhaust ports flow about 77 percent of the intake, compared to 59 percent for the iron head. This means you might be better off using a single-pattern camshaft that opens the exhaust valves later in the combustion process, because the longer the exhaust valve stays closed, the longer time the combustion pressure has to push on the piston to make power.

The charts also reveal the gains in flow from the design of AFR's optional CNC-profiled chamber design, which unshrouds the valves and improves flow by maximizing the efficiency of the valve job and port-throat design, especially at lower valve lifts.

Finally, we've included the flow data AFR cylinder head designer Tony Mamo provided us after he port-matched the two Edelbrock intake manifolds we used in this test, a Performer RPM dual-plane and a Victor Jr. single-plane, and reflowed the 305cc head through each manifold. These are the airflow numbers the engine actually sees when it's running, and it reveals that regardless of how well any cylinder head flows, it's only as good as the manifold that's attached to it.