http://www.autoblog.com/2007/07/30/model-t-takes-on-a-hummer-in-hill-climb/ OK, it had 100 HP, instead of the original 20, but still. The original article: http://www.forbes.com/free_forbes/2007/0813/112a.html
It's about horsepower to weight ratio. The speed record holder for a lot of years at our local sports car race track was a go kart, and there were lots of exotic cars running the track. With a 4000 pound Ferrari running about 7 pounds per horsepower, the go kart has to have about 50 horsepower to match it and it's pretty easy to get way, way more power than that into a go kart and the little things go around corners at speeds that scare me just watching. Getting 100 horses with technology from the 20's and 30's is cool though...