on a roots blower, like the 03/04 cobra's, you will have instant boost...with a centrifical blower, like the prochargers, vortechs, etc.. its like a turbo's intake side, with a belt strapped to the shaft....boost will be RPM dependant. 9psi will be what you see at redline...at 2000 you may see 1psi, then at 4 you may see 5psi. its linear...like i was talking about with my blower and my power "curve" it doesnt sit you in the seat like turbos do. and there is no "hit" like there is with nitrous...its gradual, and honestly, not all that fun in terms of seat of the pants.