Headers tube diameter.

Locomotion said

Just wanted to elaborate on what was said here. The TTI's are actually stepped, from 1 5/8" to 1 3/4". They "act" like the bigger size without the disadvantage of restriction downstream like a straight 1 5/8" would have, especially as you go up in HP. At least up to the point where you do need bigger tubes.

My philosophy has always been that it's normally better to lean on the conservative side for best results anyway.

CI = cast iron

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What class are you running Myron? Have you tested stepped headers back to back verses a large (what I consider large, or larger) tube header? I used 1.75 headers back when everyone was saying they were too big. Then I changed combos, and bought the 5303 Hookers. I knew I had gone the right was just pulling it out of the shop to put it on the trailer.

I ask, because I know a guy who is running G stock IIRC and he tested stepped headers and merge collectors and all that. His results mirrored mine. When the lengths were correct, the diameter was less important, especially in the collector.

That is not to say if you were just working to reduce exhaust lobe centerline, or to reduce exhaust timing, say, to gain intake effectiveness you won't find merge collectors and smaller primary tube diameter more effective, specifically when considering 4-2-1 headers.

In my experience, the testing required exceeds most budgets. That is why I was wondering how extensively you followed the step header testing. I know Joe Sherman has found nothing as of yet, but I have not talked to him in a year or so. It could be the way I port, or what I expect to see when spec'ing a cam that makes those things ineffective. What are your thoughts?