The compressor maps for a t4 and a gt3076 show that the g3076 should make much more power than the t4, it flows something like 6lb of air more on the compressor map.

But, due to the exhaust wheel they will make pretty well identical power to a t4 at the same boost, maybe 5-10 bhp more.

The exhaust wheel of a t4 is big, hence being slightly more laggy, where a gt30 has too small a ex wheel for the compressor wheel but gives good response.

Mat, I've no idea why any body would want to run that boost on a t4, rediculous IMO

Gareth, I wouldn't advise that comp ratio but have driven one at 7.2 and the word for it is raw, very un progressive, awesome feeling but in the real world not good