Haha, hey guys. Have had my head buried in work for the past few days. Le Mans Hypercars need turbos too, just as much as Redblocks do!
There are two generations of GTX3576R - maybe that's where some confusion is being generated. I personally am a fan of the Gen1 because peak compressor efficiency was higher. Gen2 got a higher flowing compressor stage (wider map) with slightly lower peak efficiency. Turbine specs are the same between the two.
For 400whp (so ~475 bhp at the flywheel) and 2.3L, the GTX3071R is the biggest I'm currently going to recommend for you Stiggy. The engine just won't flow enough to make a 76mm compressor worth the tradeoffs of operating regime and surge margin (IMO). Even at 7000rpm, 14.7psi ambient, 95% volumetric efficiency, 0.5 lb/hp-hr BSFC, and 11.5 AFR, your corrected airflow looks like about 43 or 44 lb/min assuming 30psi manifold boost pressure. At 35psi the corrected flow rate goes up to 50 lb/min.
The VE, BSFC, and AFR values are complete guesses. If those are anywhere close to correct, and you see yourself running about 30 - 35psi, then the GTX3071R Gen1 would be just about right, or a GTX3067R (also Gen1 - there is no Gen2) would also be great and would spool faster in full load and transients.
If you could only get your hands on a Gen2 then the GTX3576R might actually be better. The shape of the Gen2 compressor map is such that a 3071 becomes less than ideal at the same operating point - it's more tailored to a larger engine requiring less boost to make the same power, like a typical V6.
For smaller (2.0L - 2.5L) more highly boosted 4-cylinders the Gen1 GTX is just better suited if you stay on the small side. If you can only get Gen2, then go one size larger to get the same steady state efficiency. That will also give you more headroom up top for higher flow, but now you're talking about increasing displacement and keeping the same turbo.
