[bobcowan]

It doesn't matter how much power the engine is capable of. When you're braking, the throttles are closed and the engine is making almost no power at all.

The important part is that the car doesn't weigh very much. Most every car with driver is about 2,500#, and some a lot lighter than that. You don't need a lot of brake power for that.

If you install big brakes - like giant Wilwoods - then a power booster can make the brakes too sensitive to drive easily.

As said above a lot of high-performance engines do not make enough vacuum to feed a brake booster very well, although you can get around that with a large reservoir. With those inconsistent vacuum levels can make the brakes to variable to be useful on the racetrack.

the bottom line is, most cars just don't need them.