Never really been in to electric cars/trucks, I have 4 Nitro Monster trucks, and one on-road car, and I've been around RC for a long time.
This is how I understand Electrics work. The lower the "turns" in your electric motor, is a starting point for speed, the lower the turns, the faster your vehicle will be.... HOWEVER, The ESC (electronic speed control) will limit the faster motors. A low end ESC may only be good for 16 turns, running a 15 turn or lower will fry your ESC.
A high end ESC may have no turn limit, but running a crazy motor 10turns or lower (example, I'm sure since I was into electrics they have developed new motors) you may not actually gain speed, only lose acceleration, and not have the car to run with a mod motor. Or not have the batteries to run such a motor.
The lower the turn motor, the harder they are on batteries. So investing in a couple good sets of batteries would be a good start. I believe they were upwards of $60 for a good battery when I had a car 2400mAh or something near that. I see now they run 3000mAh +, I cannot imagine a price.
Then to charge these stupid expensive batteries, you need a peak charger to get max. performance, also a expensive piece.
This is why I do the nitro cars/trucks, add gas, go, and in most cases outrun any electric, any-day. Sure they're cool, and they can be very fast, but I'm a hotrodder, how fun is it when they're dead silent, and theirs no exhaust burning your eyes!
And if (like RdNekRatRodr says) you have a Radio Shack car, I just wasted my breathe, they don't get faster.
Here's the best RC site I've found.
www.rcuniverse.com
bonuts