What would be the definition of a "car" then? What is the weight it needs to haul to qualify? I mean they created a "car" that was smaller than a penny:
http://www.cnn.com/TECH/9711/22/micro.car/
Does it need to be a "typical" passenger car? How much weight does it need to pull and at what speed does it need to travel to qualify?
Additionally, what horsepower would you be talking about? Rear wheel? At the flywheel?
I know of cars with as little as 40hp and I'm sure there are those that had less.