It only powers the flux capacitor, the motor is still a normal internal combustion engine, which is fine, unless you need to go back to 1885. 
Should be a simple job to rip the engine out and use the Mr Fusion reactor to heat some water to create a steam powered car?
(It's always irked me the they go back to 1885 and can't run the car, 26 years after the discovery of petroleum. )
