Welp, the good thing is, you have cubic inches to help, but that will only get you so far. With that said, this is really going to come down to turbine housing choices and what configuration he wants, as well as ultimate hp goal he is trying to achieve. Configuration meaning T4 four bolt inlet flange, vs round V-band inlet flange.
GT4202 will safely support 800-900 flywheel hp, without having to kill it. (27-32PSI)
TurboByGarrett.com - Catalog
I would recommend that he go with the dual ball bearing version. This way he could get the turbo with the 1.15 A/R T4 housing and see how it performs with his 3000 stall. I can tell you that from my Buick experiences with TSL combos, (274-278 CI with GN-1 or T/A Perf heads) this same turbo with the 76mm comp wheel upgrade and dual ball bearing chra, had the best flow vs spool up compromise when using the 1.28 A/R housing and a decent stall converter. However, decent being more than the 3000 that your buddy has now. So, the 1.15 Garrett housing would be better suited for such a low stall. DBB would be a must if he wanted to see anything close to decent spool up with the 1.15 A/R. The last resort would be the 1.01 A/R split T4 housing, but he might run into some back pressure issues with such a large CI setup at high boost levels.
Now, the new Tial turbine housing look very promising, but with them being relatively new, I would seriously doubt there are very many who are running them in a similar application. Looks like they offer the 1.00 A/R only at this time in thier SS turbine housing for the 4202. It looks like a very nice, a true high flow optimized design for sure, but who really knows until there are some real world comparison results published, and or back pressure readings taken. Honestly, going from a Garrett split scroll to this single throat v-band design might only help slightly in HP and spool up. Again, we won't know for fact until we have more real world results.
If it was me, I would get the GT4202R, with the upgraded 76mm comp wheel, dual bb, and the 1.15 A/R housing first to start with and try it. Then, if he can't get it too spool, he can always go back with a 1.01 A/R Garrett housing. It's much easier to swap out turbine housing, than it is to R&R a converter. That Tial housing looks nice, but you are really limiting yourself with the V-band inlet flange setup. Part number for the Garrett 1.01 A/R turbine housing is 757707-1, and part number for the standard GT4202R equipped with the 1.15 A/R housing should be 774595-6. Sometimes the last part of the part number could be -0006, other times it could be -9006, it just depends on who you get it from. The GT4202R with the upgraded 76mm comp wheel was, for awhile, a Precision Turbo only piece. However, there are now a few other companies who can replicate this same turbo. Jose at Forced Induction comes to mind.
One last thing to remember is this, the out of the box GT4292R and GT4202R both have screw on compressor wheels, and if your buddy plans on running large amounts of boost, make dang sure he has a large enough blow off valve capacity. Some have used twin Tial 50mm blow off valves, others simply go straight to the Procharger 60mm blow off valve. What happens is, at high boost levels, 35+, when you jump off the throttle on decel at the end of a pass, if your blow off valve doesn't have enough capacity to properly vent all that excess boost, the sudden transition and reversal of the compressor wheel can cause it to come unscrewed from the turbine wheel shaft and exit the housing. (IE: self destruct and take off.)
Not too say that this will happen every time, but just letting you know that it has happened to some people who run crazy boost levels. The good thing about the GT4276 is, that the compressor wheel is the standard bolt on style. Which really helps eliminate this issue.
Hope some of this helps and sorry so long winded.
Patrick
