1 5/8" is plenty but stepped headers from Schoenfeld that go from that to 1 3/4" would be better. It's important to keep the velocity up, and going too large will kill that so I honestly wouldn't have primaries bigger than 1 3/4". We also want the exhaust to stay hot, as hot gas flows faster than cold gas. Going up in pipe size also cools the exhaust, thereby slowing it down even more. Collector size, length, and merge design is also very important, and tuning this area can garner decent returns.
Try searching for any information you can find from Mr. Calvin Elston- he's the golden god of exhaust systems. He's also been very active on different forums, and at one point had "Exhausting 101" which was a wealth of information. It's gone now though. However, one can still find MANY conversations where he freely gives out trade secrets.
Try searching for any information you can find from Mr. Calvin Elston- he's the golden god of exhaust systems. He's also been very active on different forums, and at one point had "Exhausting 101" which was a wealth of information. It's gone now though. However, one can still find MANY conversations where he freely gives out trade secrets.
