The motor in Max's car may have been a 300 horsepower 351 cubic inch (about 5.7 liters) V8 but there is some controversy (see below). It has a Weiand supercharger that is non-functional. I don't believe anyone has ever made a functional supercharger which can be switched on and off (hmm, I've recently been told that the '88 Toyota MR2 had one). In the movies, the supercharger was actually driven by an electric motor rather than by the engine itself. So, even though it is said in Mad Max (the movie) that the car is 600 hp, it was in actuality only 300 hp. However, if the supercharger was functional, it just might be possible to generate about 600 hp but the engine probably wouldn't last very long.

Source: http://www.geocities.com/Area51/Lair/3423/