I had a nice conversation with Joe Lubrant recently, and while he didn't answer your exact questions, here's part of what he said. The new Garrett center section is not compatible with the current compressor and turbine backing plates and housings. The compressor side is not a problem because Garrett is already producing "GT" housings. However, on the turbine side, Garrett is only making 4 bolt housings that match up with the import/4-cyl flanges. I didn't ask if they made one to match the T4 4-bolt flange, sorry. In fact, Precision is working to modify their 3 bolt exhaust housing/backing plate to adapt to the new GT center section, and will be supplying that to Garrett when it's done. That will be several months yet, and is the determining factor for when complete GT turbos for us will be available from Garrett. We didn't talk about ball bearings at all but I think it's safe to assume
-)) that the complete turbos will be available with or without ball bearings, since that's the whole reason to advance to the new center sections.
In the meantime, they are using a few of the new GT wheels in the current housings. On the compressor side, there is a new GT 61 mm wheel that is a nice replacement for the old 60-1 wheel used in the TE/TA 60, 61, 62, PTE/PTA 52, and 54. The compressor map for this is available on the precision web site. Click on the sport compact button, and at the bottom of the page click on map for the sc6163xx turbos. The 60-1 map is available several places online (
www.turbonetics.com, for one, and yes, I know this isn't turbonetics but it's the only url I seem to be able to remember
). The other GT compressor wheel that seems to be shipping in any volume is the GT67. This is said to be lighter and faster spooling than the old T66 wheel, but no map is available online that I'm aware of, and I don't know how it compares to the TO4R 66 mm wheel that has been out for a year or so which is also supposed to be lighter than the T66 for better spoolup but not as good at extreme boosts. I've seen one poster comment about his new GT70 but I know nothing about that wheel. Joe did give me the diameters and trims of the 61 and 67 wheels that they are using but those notes are at home so I'll have to post them later if anyone is really interested. If you download the Garrett catalog from their website and look at the maps they include, none of them match up to these wheels.
On the exhaust side, the first GT turbine wheel to be used was the GT350 wheel, used in the PTE/PTA 51 and 53. The only other GT turbine wheel I'm aware of right now is the GT-Q wheel which Joe said is supposed to outspool the old T4 P trim while outflowing the old T4 Q trim.
As for combinations, the new GT61 compressor is available with either the GT350 turbine (so similar to a PTE52) or a P trim turbine (similar to a TE62). The new GT67 compressor is available with a P trim (similar to the old PT66), the old Q trim, or the new GT-Q trim. Unfortunately I don't have hp estimates for any of these. Oh, these are available with the standard TO4E compressor cover (the "TE" housing) or the larger TO4S housing (4" inlet and bigger outlet) for an extra $100 or so. The new GT compressor covers include a baffle, for lack of a better term, that looks a lot like the booster venturis on the primary side of a Quadrajet carburetor. This lets them open up the inlet behind the baffle for better flow. I don't know how much extra this costs right now. Right now, in the TSM class, I believe that this was deemed illegal at Bowling Green this year since even though their inlet size test plug fit (or I guess, didn't fit since it's a no-go plug) the inside diameter of the baffle, the open area behind the baffle was larger than allowed in a standard compressor housing (and they have rules about when parts become available, etc). However, Joe said that this style would become standard at Precision within a year, as volumes ramp up and the complete turbos become available from Garrett.
Grr, forgot to get back to the original question of upgradeability. From the way Joe described things, I don't think that upgrading a current "PT GT67" turbo to the GT center section will be practical since the only parts that would carry over would be the wheels and maybe the compressor cover, but definitely not the backing plates and turbine housing. I'm in the same quandry you are, since I want a new turbo but kind of hate to buy one now when a much better one will be available in 6 months. However, since I don't think I'll be willing to pay for the ball bearings in any case (assuming they will carry a $500-700 premium like they do now), I'm thinking real hard about a P trim GT67.
