Heat pump? What do you mean? Ive heard people refer to the M90 as a "heat pump", is that what you are talking about or is there actually something on the motor that is called a heat pump? I always thought that the roots type blowers were put on factory cars, because of their reliablility or durability. I thought the centrifical superchargers were more effecient, less drag off of the motor, and run cooler....therefore produce more power. I am guessing that most of the 3.8 NA guys that have done this have just been bolting on a supercharger and running like 6 to 8 lbs of boost. Just wondereing what would happen with an SC, having much lower compression ratio to start with. I guess what I am asking is...........if you take an SC that is running 15lbs of boost with an M90, then compare with the same car running a ProCharger(or whatever) at 15lbs of boost, which will be overall more powerful?