Edwin, what we usually run are your basic, small wheeled,vintage style mini bikes, 6.5 box stocks , 5hp briggs motors. Drum clutches , Magnum clutches , so we can change gearing . My buddy running the briggs is running alky , all us box stock racers are pretty much just running the simple hopped-up , upgraded 6.5's. Heavy springs , jetted carb , intake . Plenty of upgrade opportunities. It's all good !