Vance & Hines "tuning kit"
I stumbled across these while buying new packing for my exhaust. I know V&H are crappy slip-ons but I decided to see if I could improve the one I have a little bit so I sprang the $15 for them. They slip inside the mid-pipe between it and the slip-on. The increase the back pressure quite a bit. I put on the narrowest one and it helped my low end a bit by assisting the EX-up but cut down the high end. I'm going to try the mid one to get a happier medium, hopefully. The best thing about them though is they quite the damn thing quite a bit and make it sound better. If you have a V&H slip-on I would reccomend getting this thing and trying it out.