The S300 is almost two frame sizes bigger than the GT35; S300 is more comparable to the GT40.  Talk to Geoff directly and tell him what I recommended and he can work off of that if you decide to go with a BW equivilant.  

Yes, the S300 is physically much larger than the GT35 (direct replacement fit for a GT40), but the performance difference between them seems to be small. This graph is pretty interesting...

Here is what Geoff said in an email to Raffi about my setup:

"I 100% agree that the efr 8374 and s300sx fmw will be excellent matches for this application, and all he needs to do is use some good headers (Even factory would be fine) then make a twinscroll crossover pipe with dual WG's...the gtx3582 would not be recommended, the gtx3576 is a better match"

Also, Supra guys seem to have good success with the S300 turbos....
"I pulled a GT35R in favor of this turbo (BW S366) and to my surprise a NON ball bearing unit was as responsive as a BB unit. And as far as power went I saw about 100-115 more hp with only 1-2 psi of elevated boost over the previous setup with the 35R." 

http://www.supraforums.com/forum/sh...ost6949092

My biggest concern with any turbo is the fact that I am going to be running under 10 psi of boost and will be wastegating nearly 50% of my flow. I have to make damn sure I have a good wastegate flow path.

 Hmmm.... Geoff is talking about the EFR 8374 which is different than the S300 series.  Regardless, figure about a 500rpm spool penalty in going with those size turbos over the GTX3576/7670 size turbos.  The bigger turbos are more efficient at your target power, but at the spool penality.  I figure about 4000rpm vs. 3500rpm for your target boost level.

I'm going to post my BW Matchbot data, so that anyone can look at it/comment on it. If nothing else it will show what kind of correctly flow rates I am using on compressor maps.

The first link is setup for running a BW EFR 8374 with a 1.05 A/R divided T4 turbine housing. The thing that I am most concerned with is the engine DeltaP going to -6psi at 7500rpm.

Matchbot Data A

The second one shifts the rev range up 500rpm to see the flow all the way to redline. I left the pressure drops, restrictions, etc the same, but did update the theoretical volumetric efficiencies.

Matchbot Data B

Also, here is a compressor map of the BW S300SX FMW that I plotted the corrected air flow values onto. Each dot is 1000rpm apart, starting with 2500 rpm and going to 7500rpm.

Obviously compressor maps are only half of the decision and turbine maps should also be analyzed...too bad I can't get my hands on them. That is where my communication with Full Race has come into play and why they are suggesting the BW turbos (specifically the S300SX FMW) over the Garrett counterparts. It seems like the GTX3576R is the only viable Garrett option, but they still feel the BW turbo is the way to go.

I matched a 7670. With 0.83 A/R.   Personally, this is what I'd do for a fun street setup but this turbo will be pretty much maxed out.  The GTX3576 will have a bit better efficiency, reduced back pressure, and some more head room.  This turbo I matched sacrifices top end efficiency for bottom end spoolup.  The boost pressure is low enough that the compressor outlet and intake manifold temps aren't crazy high.  Don't worry about the negative deltaP.  Many OEM applications go negative 20psi; that's the cost of having a fat bottomend.  For a track car, I would go with a bigger size.

Matched 8374 in 0.83 A/R.  The first point is at the surge line.  Both matches should be fairly close... well, just for comparisons sake. 

I really like the way the 8374 looks, but see a couple of potential issues. First, the 0.83 A/R housing is one with the internal wastegate and matchbot shows 45% wastegate flow. The EFR Technical Brief says that ~40% is the max wastegate flow, so I need an external w/g. I could wire the interal one closed though, I guess. Also, it is a single scroll housing, not twin scroll.

Second, I'm not sure the stock NSX engine with a compression ratio of 10.2:1 can handle 11psi of boost pressure reliably. It makes the compressor and turbine maps look nice, but will the motor actually hold up?

Also, I'm curious as to how you chose those volumetric efficiencies? I used the attached map that is specific to the C30A...then to be conservative (and account for negative DeltaP) I knocked 5% off of each value plotted. The reason that I thought this would be close to correct, is that matchbot was saying I would be making ~460.4 bhp with 8psi (so ~405 whp with 12% drivetrain loss) and I have seen NSX's that run 8-9psi and make 400-410 rwhp. At 8psi and the volumetric efficiencies you listed, it is estimated to make 429.2bhp...so ~378 whp. Obviously these are estimates with a large amount of possible error, but it was close to what I thought was correct.

Any thoughts?

I just put the boost level to 0 for all the rpm points and adjusted the VE until the peak HP number came out correctly. I just realized I made a mistake though, and forgot to change the BSFC (rough estimate for boosted application), so my VE values are off.  Maybe try with 0.46 from the midrange to the topend for naturally aspirated.

For the turbine housing, just adjust the expansion ratio so the points fall on the next housing up with twin scroll.  I just did the 0.83 in both cases (with appropriate turbine wheels) to show a more direct comparison.