When considering your choice of motor have a look at the wattage put out by the newer brushless stuff. Back when Cats and Cougars were current racing cars 12 turns was really hot stuff that you had trouble getting to last 5 minutes. Nowadays, just to compare the power output a 13.5T brushless is pretty close to the power back then.
If you plonk a 6.5 into either the Cat or the Cougar the drivetrain will last about 5 minutes or so along with the car being totally overwhelmed with the power.
I reckon a 9.5T would be a civil choice for the car and is nice and smooth in a 2wd, which is great if you're coming back into the sport.
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