If you make no changes to the motor or air intake, you can put all but the most open slip-ons on the bike. In example: any HD SE models, V&H, Sampson, Kerkers ( $225 at cyborg cycles), Rolling Thunder pipes with no larger than the 1 1/4 Baffles sound good and are only $200 bucks. They will not lean you out enough to hurt a thing unless you open up the air intake as well as in stage 1 etc. If you go to 2 into 1 or True duals then you will need to re-map most definitely.
Magnum