The engine just runs better, with the stock Assoc. muffler or the dual chamber muffler, you've got to rev the engine to fill the muffler with exhaust before the engine will run good. With the RDLogics pipe it seems to start better, is much quieter, and has the flow to let the engnie run better. I've only run the pipe one day, with these darn MTx3's had other things on my mind.
The stock pipe is not a one piece, a one piece pipe has the header mounted to the muffler with springs rather than just a silicon tube shoved over the header and muffler.