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When I measured the OEM truck type manifolds, They only ended up around 2" inside or thereabouts. For my twins mounted almost direct onto the truck manifolds ( with some modding and re-welding of course ) I opted for 2" ID Sch10 type pipe. Just didnt seem any sense going bigger, especially when the hole inside the scroll of the turbo was only around 1.5" anyway.
I have a log manifold on the PS, I think its 2.5" or 3", uses a 2.5 cross over to the DS-I used that because
thats what the V band was on the log. I had planned on a truck manifold on the DS, but had a tight
fit Pat. Perf. header laying around, so i used that. Not sure how the 4 ind. pipes into a 2.5 affects
the velocity, as opposed to a truck manifold. But I was thinking of switching to the truck manifold to gain
better plug access. I have a short piece of the orig exhaust pipe so i was going to use that as opposed
to a V clamp. The pipe actually is around 2.5", but as said the manifold is 2" at the flange. Prob.
blowing thru a 2" into a 2.5" doesn't do wonders for velocity. GM designed the firing order for what
they built it to do, always wondered if it could be altered to comp. a turbo, if there was some advantage.
Was doing some more head scratching and I think I am just going to to 2in log that each feed into the merge at T4 flange. If I can make that work, that would be optimal.
So as I am stuck with crappy D port heads, and I want to minimize the amount of fab work required. Thinking of laser cutting a flange that has circle ports for SCH10 1.25 OD stuff. Square dotted is head port, circle is the elbow diameter.
Should I be concerned with the overlap?
Most of me is thinking is a 383ci motor pushing a T4 76mm and its overkill to begin with so the overlap won't hurt.
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