Originally Posted by
Cosmo
I'll be the first to admit that I don't completely understand why things work the way that they do, but why are the tubes smallest at the head, and then get bigger? Does that increase the velocity or something?
Nice looking welds, by the way...
I believe it's similar to the idea that most turbo outlets are significantly smaller than the end diameter out the rear. The o2 housing then get progressively larger and then the actual downpipe usually goes 3".