Apparently 15 tooth is the smallest pinion with the T8's stock. Smaller and the Motor fins hit the diff outdrive.

I think its down to 13T if you file down the fins.

Most seem to be using a lower Kv motor and gearing up a bit.

Also heard 4mm motor screws require enlarging the motor mount slots.

DJ from ofna also recommends putting a foam block under the rear of the motor to stop it bending the motor mount on heavy landings. Check out 'ofna live'.

I think thats right from memory. All info from surfing here, RC Tech thread and Ofna.

Cheers!