There are definitely variables that I can't duplicate. The head pipe portion before you get into the actual muffler on mine is a rossi unit and is therefore somewhat different in layout than a Jett or ultra thrust, I kinda guessed on the length of the "tube inside a tube" as well. Im not an exhaust guru by trade. I did, however, email one by the name of dub Jett and asked for some advice on it. We'll see if he writes back. I wouldnt blame him if he didnt.
Speedracer what field do you fly at? I drive by one on my way to San Francisco all the time. Seems like its about half way between San Fran and Gilroy. Im from Fresno area so I dont really know the lay of the land there, but I was always interested in stopping by.