Modifying or shortening the stock muffler is the only way to get an aftermarket sound while keeping the stock catalytic converter. None of the aftermarket mufflers have a cat. The mod involves cutting a hole in the rear of the muffler OR removing the last 3 to 4.5 inches of the muffler. The cat is in the front section of the muffler.
Two basic ways to do it:
1).. Use a hole saw to remove the exhaust tip OR
2)..Cut off the end of the stock muffler (by 70-120mm) and re-install the end-cap.
The rest of this page is about the 2nd method.
I shortened my stock muffler by 84mm (others on the forum have done 100mm and 120mm).
My guess is: shortened by only 84mm, the rear muffler section is larger, which might mean a deeper tone.
You can use it with or without the end cap. I drove my rebel 500 without the end cap – it was much louder than stock and sounded great. Adding the end cap reduces the loudness by 3 dB or more – it is still quite a bit louder than stock.
Tips
You do not need to cut clean through the muffler – just the outside shell.
If you do cut clean through the muffler, you will be cutting two small pipes – this does not matter since the two pipes are not used.
If you want, you can do the projects as two parts: 1) cut the muffler and then 2) remove the end-cap from the part you cut off and then re-install the end-cap on the muffler. The advantage of this is that you can be driving around sooner evaluating whether you like having no end-cap and then later you can take your time removing and re- installing the end-cap.
If you are not sure what length you want, I recommend 85mm. The halfway point of the rear muffler section is 77mm.
Rebel500 