The gtx3576 was made for the 2.5 ltr motor by garrett because me and some others asked for it directly. It was a simple project of swapping parts and listing parts in the catalog so there was little work to make this a reality. Its a great turbo, really has a wide power band and has enough turbine to get that heat out of the turbine.
Its also great for twin turbo V8's where we have the same issue of the turbines being to small. Most people dont bother to measure the turbine pressure and only measure compressor pressure and as a result, They dont know what they are missing.
The GTX30R will not make GT35R power period. Dont be fooled. It does make more then the GT30R as it has a larger compressor. On cars with a big external gate that can bypass a ***** ton of exhaust past the little turbine, some good power can be made. The GTX offers about 10 to 20 % more compressor flow at higher boost. At lower boost pressures of pump gas, I prefer the standard GT30 and GT35.
something to think about... Running a GTX30R hard on E85 makes alot of trq. More trq then top end power. That can be distructive on parts. Simply swapping that turbo out for the GT35R and or GTX35R on the same engine setup and boost pressure makes another 100whp+. I like free HP,big top end power and I dont like a turbo running at its max. I have swapped them all out back to back many times over the last few years. If you have the fuel system, Get the larger turbo.