[Joey]

Unless you had a serious excess of current being passed to the one motor, or adapted additional cells to the thing to compensate for the increase in draw, the motors wouldn't get as much power together as either one of them would alone. Switching pinions in any case only accentuates what's already being done, good or bad - if you put a high-speeder on, then the motors wouldn't have the torque to push it very fast. If you put on a low-geared/drift pinion, then acceleration would still be bogged from the lack of power.

Not to mention it's a nightmare getting six cells to fit on those things, let alone six cells and another motor. But if you really want to do it, then it's possible.