[joyridin']

Most of the pipes I see go from the 4 tubes into a 3" or 3.5" diameter pipe, then go into a 4" muffler, then back to a 3/3.5" outlet. Whatever brand I have on my car are 4" diameter straight through. They have a baffle about 10" long that is noting but a few pieces of plate welded to a 3/4" pipe down the center. Compared to most that are necked down, or go through mufflers, these are about as free flowing as you can get. I am not sure if all Arntz/Butlers had them or not.