So, it is the Volumetric efficiency that we are changing!! Not so much the amount of air flowing through the turbo.

Fitting the T4 results in:
Lower back pressure
Lower outlet temperature.

So the power is increased, but so is the lag.

RobetM - Thank you for an ace link.
Xr2wishy - "with a given resistance, i.e. inlet ports/cylinders/throttle body all pipework you need a given flow of air to maintain this pressure.
if you have more flow and resistance is the same, then the pressure would be higher." This is what I was trying to say to my brother in law but after a couple of pints I failed. LOL
Chips - Looks like you REALLY know your stuff. Did you read the PDF before posting?
Crazycage - If you could some how get a T2 to boost 2 bar, using an external power source, then yes you can have your 500bhp? Do that and your rich.

Maybe getting that new dyson electric motor and putting that in a T4 would be intresting. Spins fast enough but doubt it would have enough torque.
http://www.telegraph.co.uk/technolog...ew-vacuum.html