Hispeed

I am playing around with the idea of buying a turbo for my car. Just curious though... My car is not really a daily driver and is only driven on "special occasions" if you know what I mean. With that said my understanding is that an air/water is much more efficient intercooler for a track car since you can ice the water. One person said that his air temps are 50 degrees while ambient is 100. By the end of the track @18psi, air temps are 86-100 after the run and then it goes back down. Intresting as I like that idea. Furthermore, I have noticed that most of the imports in the pro class run both.. air/air and air/water.. is this feasible for a street car? I was thinking more along the lines of just turn down the boost on the street. Lastly .. how much would a setup for air/water cost?? Thanks.