Join Date: Jul 2008
Location: southwest lower Michigan
Re: 71 Chevelle ZZ502 Headers Needed !!
Yes, round square or oval will work on the D-port head. The thing to look for is not blocking the sides or the top of the port.
Entire port opening in the header being big enough to not block any of the D-port head opening....then it doesn't matter what shape the header port opening is.
Best would be an oval or round big enough that the bottom of the header port opening is below the D-port opening in the head, making a reversion dam along the bottom of the port to block backflow into the cylinder during the overlap period around TDC exhaust stroke when both valves are open..