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Hi,

I having been reading up on a bit on manifolds and I have question for the exhaust experts. :) I will take an example to illustrate this question.

Say my car currently has 2'' pipes in its manifold - 4 cylinder. Now assume I design a new manifold which has just the same fitting as the OE but with some subtle variances. The design would be 2'' at the intake, expanding gradually at the mid-section to 3'' and then to 2'' at the place where it joins the Manifold base (so no coupling, reducers etc. required). This will be mated with a cat back system with 2'' piping all around right upto the muffler intake.

In my opinion, this design should improve scavenging and improve flow of gases. The advantage is also that it will be just like OE but with reduced sound (unlike header design), and there is no need to mess around with O2 sensors etc.

Question is, what kinda gains can I expect in this design, both in terms of torque and bhp. And at what typica rpm ranges will this kick in?

Please give in your thoughts and views on this and do feel free to critique this design.

Thanks,
-P.