D ports vs round port heads
 

Ok what are the HP limits with D port aluminum heads vs round ports in a turbo application ?

Street application? Probably minimal. I believe I've read before you run something like an s480, is that correct?

That thing will probably make every bit of 1100 hp...to the tire, at about 15 psi on an aftermarket headed 455, regardless of what head is on it. In fact, I'd bet it would do it on a set of as cast D or round ports if you push the boost up a bit.

I'd be more worried about a factory block holding together than I would be concerned about which port type I'd be using.

That being the case, something like an SD 290cfm KRE D port with a properly sized cam in a normally aspirated 460" Pontiac will typically ring the bell between 550-570hp. With something like an s480 pumping an additional 14.7psi into it, you're in 4 digit hp territory. Knowing you already have D ports which your hot side is designed around, I'd do either the Edelbrock D port or the KRE D port, which my preference leaning towards the KRE product. I don't believe you're going to see noticeable gains in a street application with a round port to make the hassle of redesigning your hot side worth it.

Thanks JL Mounce

Since both heads have the same valve size and plenty of meat for porting, the limit in terms of the D port head is the area at the Exh flange for bolting up a header bigger then 1 7/8" .to 2".

Since there Aluminum though you could weld and make them the port area needed at the flange to better match what that nice big valve can do.
Doing this you could get round port headers to maybe work, but I don't think it's necessary.


That being said, SBCs with there 1.60" Exh valve make 1100 hp with there Exh port size they can go to when ported, so I don't think if your shooting for 1100 hp with a aftermarket D port head that you will be disappointed.