21.5 Gearing
#4
With 17.5 in 12th we are already using the biggest pinions available with the smallest spurs we can get our hands on... You will need to overdrive the car to get all the power out of that motor in 12th. Probably talking spurs smaller than 72t and pinions just as big.. You will probably need to change to the old 12l3 'stealth' axle and small diff rings to make this work.