Picking twins is really pretty easy. You look at the estimated HP (1200 in this case) and you divide by two. So the question really is what turbo will work good at 600 hp and 30# of boost.
At only 600 hp AND 30 psi a T70 will be real close to compressor surge. ESPECIALLY if you dont keep a close eye on turbo inlet and outlet restrictions. As you start approaching 1300 to 1400 hp total OR you start looking at the 1200 hp at something closer to 25# then the T70's start looking pretty good.
A pair of T66's map out real nice for your senerio. If you keep the inlet and outlet restrictions very low a pair of T66's will feed the 1200hp anywhere from around 24 to 30 psi AND be operating at peak compressor efficiency of 76%. This is a pretty high compressor efficiency wether you're talking old school or new style (GT) compressor wheels.
The GT4294 which has the 70.3mm compressor wheel, which I believe is the gt40/70mm that John was taliking about maps out real nice for the given senerio. Infact the compressor section will be knocking around the 77 to 78% compressor efficiency range. From a pure comp eff standpoint a pair of these would be the winners. The only thing that makes me wonder about a pair of these is that they wouldn't hit the " I think these may be a little to small now" until you started pushing around 1600 hp! You would think that if 1200 hp was the true goal that a smaller pair may be a good choice d/t better spool up. Then again too much power too soon may lead to skid marks some where other than on the track
HTH and just remember that when you pick a pump for any application the amout of flow and the pressure you want it to be operating at are equally important.
Jason
