take your spark arrestor out.
then look in the pipe.
you will see a steal wall like 5 inches into the muffler. the wall has a small like 1 inch hole in it.
cut behind that wall.

then block all but 1 pipe in side the muffler. eather keep the big one or the smaller one. look at this pic. the ones with the x mark on i blocked off. the big one i kept. you can keep the big one or the one that is up colse in pic that i kinda crushed. i think you get more porformance gain by running the slightly smaller pipe than the big one i kept. Very Very loud. sounds pritty good if you like loud. not a mod you want to do if you trail ride or have grumpy neighbors.
http://teamxracing.cjb.net/index.php...ost&id=1372978

then weld the cap on and you have a pipe that looks like this
http://teamxracing.cjb.net/index.php...ost&id=1210476
http://teamxracing.cjb.net/index.php...ost&id=1210450
http://teamxracing.cjb.net/index.php...ost&id=1373440
http://teamxracing.cjb.net/index.php...ost&id=1373463