Stainless pot scrubbers work fine as do the copper ones. I cut mine open, added more holes to the inside pipe ( I left the converter intact) and made a second small exhaust tip hole with the extra piece I removed from the single tip. I then added pot scrubber as sound packing and finished the bottom with some hardware wire screen before puting the end cap back on. The screen keeps the pot scrubber from blowing out in little chunks. The end result was better flow and about the same sound as stock. Not sure if it really gained much over-all. I would say after having my end cap fall off and having to riding home that way to fix it, the modified pipe perfoms someplace in between wide open (loud) and bone stock, roughly 2 MPH faster than stock. Not really worth the trouble. I would invest more time getting your jetting and needle set correctly and selecting the right final drive sprocket for your riding conditions, speed desired etc, to be time and effort better spent. For me, the best gain was jetting and getting a 40 tooth sprocket. I ride at 27 MPH at 3/4 throttle and don't feel the need for more. YMMV
