Yeah, the thing that hurt it, was the large turbine. Also don't have any other information to go with it... Was it tuned? Was the tuned changed much? What about exhaust housings..??

Too many variables.

I honestly believe that the 94mm compressor using a GT40R turbine would be a good match. Hell look at FP. They seem to do it all the time, but single scroll.

Using a 1.01 or 1.15 A/R T4 divided housing on the GT40R turbine with the 94mm compressor, I think would make for a rather good spooling 800HP turbo and would be a good stop-gap between the GTX4088R and GTX4294R.

 

Not least worth mentioning the MUCH larger compressor wheel? How do you figure the GTX4294R compressor would be better spooling than the GTX4088R compressor?

FP do quite a different thing - for a start until recently they have predominantly used their own 67in/94exd compressor (versus 70in/94exd on the GTX4294R) on a T04Z core which has significantly smaller turbine wheel than a GT40, and called it a FP3794HTA. From what FP have said, even the "Super94 HTA" turbo has a slightly smaller (but larger trim) turbine than the GT40R turbine!

You mean the run of the mill GT4094R? They are pretty laggy beasts, at this stage I can't see what advantage they'd have over the GTX4088R - certainly can't see why they'd have any response advantage.

 

The GTX 94mm diameter compressor wheel on the GT40 turbine would not be a good match for two reasons. It would reduce the blade speed ratio on the turbine reducing the turbine efficiency making the turbo laggier. The 94mm compressor wheel itself is heavier than the 88mm in mass plus larger diameter which increases inertia exponentially. So the increased mass and radius at which the mass is located will make the turbo laggier.

With how much the GTX 88mm diameter compressor wheel flows, ~85lbs/min, it would actually do quite well on the GT42 turbine.