Totally pimp your engine with NOS. Nitrous Kit for a Yamaha Rhino http://www.utvheadquarters.com/inc/sdetail/1876 I have no idea how big the engine in a Rhino is just thought it looked interesting op:
660cc thumper in the rhino. my buddy has one, they are a lot of fun, but they're loud and all open.. if i could just figure out how to get the suspension off one and under my truck i'd be in heaven