You could mount a stack of 30 pop bottle rockets on the roof, tie there fuses together and then run one long fuse to the motor can.
Just make sure you mount them real secure and have a fire proof pad between them and the Lexan body.
Okay I cannot believe that nobody mentioned this so here it goes... if you want fast and money isn't an object, buy yourself a li/poly battery and a low turn hand-wound motor. The li/poly batteries weigh fractions of the weight of standard nmh cells and produce 12 volts!
With this combination you have a much higher power to weight ratio and a lot more potential.
Just don't think of turning or how many fragments the car will be in when it hits a pebble.
Top speeds that can be attained very much depends on the room you have. With a 12 turns on the Heemstede track in The Netherlands I have managed to go over 80 Kph (about 50Mph) in a normal 5 minute run despite the fact that the speed trap is only 8 meters before the end of the straight. On smaller tracks 65-70 Kph can be reached quite easily with 12 turn motors. Moreover on smaller tracks the amazing acceleration of electric cars will win out over the sheer speed a gas powered car has to offer.