For our baseline numbers, and to let you know what a variety of stock and aftermarket heads flow in untouched form, we commandeered the flow bench at Auto Performance Engines. Remember that flow benches are like dynos and there are slight variances between machines and conditions. We're not trying to demonstrate how well or poorly certain cylinder heads flow, just provide a comparison between heads and show the benefits of a little port work.
To demonstrate how spending just an hour per port can really help cylinder head flow, we began grinding and polishing the intake and exhaust port of our 452 casting factory head while Kevin at APE did the same with the Edelbrock Performer RPM. It was then back to the flow bench to see what affect our port work had on intake and exhaust flow.
From our tests, it is pretty obvious that even the best un-ported factory big-block Chrysler cylinder heads leave a lot to be desired when compared to mildly ported versions or aftermarket heads. Also, while the percentage of flow gained by porting was greater on the factory head, the aftermarket heads start off a lot better, so it's more difficult and time consuming to make big gains. Any of the cylinder heads we tested could certainly be made to flow better, but we limited the time we spent on port work to more closely imitate what the majority of our readers would do, or could afford.