How to get higher top speed, higher acceleration and better performance:

You need 6 or 7 or however many you want watch batteries, those flat silver ones.

Tape them together in a line (-+-+-+-+ etc) leaving the ends open.
Cut or remove your old battery case and but the new power bar inside where it used to be.

Attach the positive and negavtive wires from the car to the positive and negative ends of the battery.

If you do this wrong the car will go backwards...

Why should i do this...

The Logistics:

Weight:

Watch battery: 2g approx
Regular battery: 10g approx

2g * 7batteries = 14 grams
10g * 4batteries = 40 grams

You cut 26 grams!

Power:

Watch Battery: 1.5 volts
Regular Battery: 1.5 volts

1.5 volts * 7 = 10.5 volts
1.5 volts * 4 = 6 volts

You gain 4.5 volts!

Power to Weight ratio:

10.5 / 14 = 0.75 volts/gram
6 / 40 = 0.15 volts/gram

CAUTION: I would not try this without a heat sync, you WILL fry your engine!