Stock/Out of the Box Flow Numbers:
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.
The added benefit of porting
9 The APE ported Edelbrock...
9 The APE ported Edelbrock head showed improvement on the flow bench as well, with an impressive 305 cfm on the intake side at .700 lift. Exhaust flow improved from 232 cfm to 244 cfm, also at .700 lift. Average flow was up significantly as well, indicating that time porting cylinder heads is definitely time well spent.
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.
10 We wanted to show you...
10 We wanted to show you a comparison shot of two intake ports as well. The port on the right was treated to a complete porting job, all the way down into the chamber. While not necessarily wanting to make the port larger, simply cleaning up the port will achieve gains in flow. The intake port on the left has received just a simple
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.