There are some engine builders that produce drag, paved oval track, dirt oval track, pulling tractors, etc. But, when you get up a certain level, builders tend to specialize in just one form of racing. Why? Techology and $$$$ are the main reason. For example, in our past life of dirt Super Late Model, the "race for a living" World of Outlaws types would have 10-12 engines in rotation. It takes a large shop to service more than 2-3 of these teams during a season. Why does it require so many engines? For the different types of tracks they compete on----different cubic inches, different torque curves, etc.

At that level, it's not a poor man's hobby!