[quote pid=1887 author=peteg40 date=1214249297]there are quite a few variables - like gt inlet or big valve head which would make the car faster but with less boost[/quote]
This is true, its easy to achieve a high boost back pressure(cos thats what it is) when the air has nowhere to go(ie standard spec engine), once you start to play with other components such as manifolds/cams/heads/valves/throttle bodies/intercoolers/pistons etc.... then you can see that back pressure within the intake system be reduced, this does not necessarly mean a loss in performance,but that your engine(system) is moving the air more effeciently when producing the power. Don't forget that the more boost (backpressure) you have then the greater load the charger is putting on the engine and therefore more energy is required to turn it.
It all about achieving the optimum from many varibles.
Or am I just talking dribble................... :/