Corrected entry: It would have been a lot easier for Doc to construct a rudimentary rocket using gunpowder as the propellant than the highly unlikely solution that he ended up doing. He could have attached two pipes, either side of the car. Gunpowder from bullets, shotgun cartridges etc. Wouldn't even need the railroad wheel conversion although I reckon would be better on rails than a dirt road.
Bodragon
27th Mar 2018
Correction: A rudimentary rocket is in no way a better solution to their problem. It would be highly unstable and unlikely to produce enough thrust. A rocket used to accelerate a car to 88mph would need a much more suitable fuel than gunpowder.