[Excaliber]

Good stuff Byots!

I found the quote from Keith Craft for additional data on the subject. The original question was about C8AE-H heads (390-428?).

"The Edelbrock and Shelby heads are better than the stock type type heads such as the ones you listed. The stock 427MR heads can be made to work real well and are a little better than the Edelbrocks out of the box, this is why we port them. The High Riser head is a real good head and can be made a lot better with work like fillling the floor on the intake and porting. We have done some HR stock heads that we have ported and filled the exhaust and intake floors and got 380 intake and 260 exhaust. The problem is it cost a lot of money and people just go to the aftermarket heads unless the rules do not allow such as in NHRA Super Stock."

I've heard (many times) that the MR heads were "almost as good" as the High Riser heads. High Risers don't have the exhaust cross over to warm the intake, which would make them much less "street friendly" in cold climates, and they require a matching High Riser intake manifold. My guess is that up to 6000 rpm or so it's probably true the MR vs HR are fairly equal in performance, after that you might want the HR, Tunnel Port, etc.