I recently cut down a set of pipes by about 3 inches. The stock pipes have three chambers with the exhaust going to 1, through a tube to 3, back into 2, then through a tube and out. I did the equivalent of the half-pipe mod, allowing the exhaust to go out directly from chamber 3. It gives me the amount of sound that I want and the pipes don't look unnaturally short.
Quick instructions for what I did:
Remove the pipe from the bike, and remove the two bolts holding the exhaust hanger on. Get a thick board, like a 2x4, grasp the pipe by the sleeve, and pound the inlet against the wood until the sleeve slides down. On older pipes it will slide down about 4", on the newer ones only about 2".
Mark the sleeve where you want to cut, put tape on the side you want to keep, and carefully cut all the way around. Slice through everything about half an inch in from the end of the pipe. Slice through everything again about 1/4" up from where you cut the sleeve.
Slide the sleeve back into place using something softer than metal to pound it (like a piece of wood), then bolt the exhaust hanger back into place. Put the end cap into the end of the sleeve, drill a couple of holes and pop-rivet it into place (or you could use screws).
Put the pipes back on and enjoy.
I just used about 10 fine-toothed hacksaw blades to cut through my pipes, since I didn't have an appropriate power tool. The only issue I have is that I can see where exhaust is escaping at the edges of the sleeve. I'm going to take them all back apart, paint the sleeves black, put some hi-temp silicone around it to get a better seal, then put them back on again.
I'm still deciding if I want to run permanently with the modified pipes or go back to the louder carbon cans that I've been running for several years. For me at least, there is such a thing as too loud. 8)
