These UMA Racing track proven gearbox ratios have been tried and tested so you don't need to figure out for yourself. Solid build quality and precision machining of gear sprockets should last you many races. This gearbox should give you shorter and closely spaced ratios than the standard unit.
Suitable for drag or circuit racing, not so much for standard engines for street use.
Gearbox Ratio (Counter shaft / Front Sprocket Shaft):