I had never heard of a Sizzler before, so I had to do some research. Those were part of the Hotwheels line, the cars were battery powered and used an open can type motor. I would expect that the motor is intended to be run at a low voltage, maybe 3 volts. In that case it would be a rocket at 18-20 volts, but its life might be short. BSRT had high performance motors of this sort.
