i have a rumble pack can (purchased from hi performance engineering) on my 04, 800 pro-x2. stock pipe. ive heard some saying that im actually loosing some horsepower with the aftermarket can, and im better off running the stock muffler. description on the rumble pack says you gain a few horse, but obviously this may be just a sales pitch. i know stock muffler is a bit heavier, which im not concerned if it will offer better perf. i appreciate any input, views on this. thanks all. Allen.