ok, here is a mod to kick some racing ass.
go to solarbotics.com and get one of their mini pager motors.
these motors really kick cause they have to be able to roll a big wait for a vibrator, but the shaft is just big enough for the black gear. then cut out the very back wall the motor holder because the motor is a tad bit too big for the car. then tape in the motor and watch it leave tire tracks