The standard car comes with an 87T spur gear, the 81T supplied with the champ pack is an option part, but I personally just run with the 87 fitted.
The 87 spur gear accomodates 17-20t pinions, the 81 will allow you to go a bit higher, 21-25t pinion.
However, I run mine with a 5.5 motor geared on 21/87, achieved with a slight modification to the motor mount- this is done by taking the cam (the piece of the motor mount which mounts onto the motor), which tapers down towards the lower bolt hole- If you thin down that taper a little more, you can then get a 21t pinion to mesh.
Tom
PS We've also found that the new blue aluminium motor mount from Yokomo does allow you to run a 21t pinion with an 87 spur without any modification.
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AE - Novak - Pro-Line - Reedy - CML - Atomic Carbon
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