There are some good articles on this subject on the web. Vizards article is popular, although hard to follow at times. Anyway, its pretty well established of the 3 types of mufflers (chambered, turbo, stright through), that the straight through muffs are the only ones that flow as much or close to an open pipe. I also think people typically over pipe their systems, which make unecessary noise. Remember, 2.5" is good for 500hp. How many have less than that and run 3"?