"I have on my GT40s.com forum a fellow who is an exhaust consultant for GM, does special projects for them, and he said he'd do the flow calculations, proper lenghts for intended use, etc. once I provide him with all the info he needs. Of course I'll share it here as well whatever I get."
I am curious to know if he asks for the cam lobe profile and intake runner lengths. If not, he ain't gonna get anything useful. Let us know what he comes up with and I'll compare it to what we know.
The smaller Nismo header at 1-5/8 OD primaries, is still too big for an ITS motor. The stepped Nismo, as sold by RallyeSport and Rebombo, er I mean Rebello, would be better at 1-1/2 for the whole length. They're too big too, but a step in the right direction. The only thing I don't like about the Nismo layout is the collectors (oh, they're too big also) make it very difficult to equalize the lengths of the secondaries.
The Sam Neave header if 1-1/2 could be one of the best commercially available options at this point. We never tested one, but it is very similar to an old Clifford Research, which was probably the closest thing in performance to our ARRC header.
Regardless of what you run the key is to optimize your mixture for best power. That means real instrumentation and dyno time.
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