I posted some of this in the GT upgradeability thread but figured it deserved a new thread.
Ever since Garrett announced these, we have all been waiting and waiting for more info. I spent some time on the phone with Joe Lubrant of Precision and wanted to pass on what I've learned as of July, 2003. First, Garrett is selling complete turbos for other cars but they do not have a 3-bolt turbine housing so they aren't selling them for our cars yet. Precision is working on adapting their turbine housing to the new center section and will be supplying that to Garrett when it is ready, which may be several more months. At that point vendors will be able to order complete units with either plain bearings or the double ball bearings, instead of assembling them themselves, if they so choose. For now, Precision (and others) are buying a few different sizes of the new GT wheels and using them in their current turbos, with the same housings and center sections we've seen for the last several years. This means that you most likely won't be able to upgrade a current "GT" turbo to a true ball bearing GT turbo, since only the wheels would carry over but not the backing plates, center section, or housings (Joe didn't say this explicitly; this is my summary of several things he did say). The wheels are lighter than the corresponding old wheels for better spoolup, and are more efficient. In Garrett's terminology, wheels are specified by their inducer and exducer diameters, where the inducer part is where air or exhaust enters. So, on the turbine side the inducer diameter is larger than the exducer diameter, and this is reversed on the compressor side. If you take the square of the ratio of the smaller diameter to the larger diameter, times 100, you get the "trim". This is useful if you are comparing a series of wheels with one diameter fixed, for example the exducer diameter on a set of compressor wheels (the outer, larger diameter, so they all fit the same compressor housing), since if everything else is held constant the airflow should be proportional to the trim. For example, for the 60-1 compressor wheel used in the TE60 (and others), the inducer diameter is 2.324" and the exducer diameter is 3.000" so the trim is (2.324/3.000)^2 * 100 = 60. Or you can just think of the trim as another arbitrary part of the name of a particular wheel
. Manufacturers also use names for the trim, when they are changing both diameters at the same time. Best known examples of this are the TO4 series P trim (inducer diameter 2.922", exducer diameter 2.544", so 76 trim) and the Q trim (inducer diameter 3.111", exducer diameter 2.693", so 75 trim) turbine wheels (yes, there are also N (inducer diameter 2.922", exducer diameter 2.071", so 50 trim) and O (inducer diameter 2.922", exducer diameter 2.296", so 62 trim) trims, but they don't seem to be as useful as other choices in TR turbos).
The first GT wheel that was available in turbos for the TRs was the GT350 turbine wheel, used in the PT 51 (70 trim) and PT52 (76 trim) that have been available for about three years now. The only other GT turbine wheel that I've heard mentioned is the GT-Q Q trim, with the same dimensions as the old Q trim (2.69/3.11") but lighter and with higher efficiency so it should make more power than the old Q trim and spool approximately as fast as the old P trim.
On the compressor side the first two wheels out are the GT61 (inducer diameter 2.416", exducer diameter 3.227", 56 trim) and the GT67 (inducer diameter 2.620", exducer diameter 3.310", 63 trim). The compressor map for the GT61 is available from Precision (http://www.precisionte.com/sportcompact/Maps/SC61.pdf). Comparing this to the map for the old 60-1 wheel (http://64.225.76.178/catalog/compmaps/fig9.html, among others), the GT61 flows about the same maximum amount of air, enough for about 600 hp max (my estimate from the map, not a spec from Joe), but the GT61 is more efficient and maintains this efficiency to much higher pressure ratios (to at least 33 psi vs. about 27 psi at 50 lbs/min airflow or about 500 hp). This means that on a stock headed stock intercooled engine that needs to run lots of boost, the GT61 will make more power. With ported heads or GN1s where more hp can be made at lower boost, the GT61 still wins due to the better efficiency but the difference will be smaller. So far I haven't found a map for the GT67 but Joe described it as similar to the old T66 but with higher efficiency and again, a much larger efficient region extending to well over 30 psi boost. I've heard a GT70 wheel mentioned but have no info on it. There is also a 66 mm TO4R wheel available, which is also lighter than the old T66 wheel and more efficient at lower pressure ratios. It would be interesting to compare the maps for the GT67, T66, and TO4R 66 mm when they are all available.
Now, on to complete turbos available from Precision (I'm sure the other vendors can assemble comparable units but I have pricing from Precision). A good summary of current non-GT turbos is available at http://www.gnttype.org/techarea/turbo/turbowheels.html. The old 60-1 compressor wheel is used in the TE60, PTE52, PTE54, and TE61 turbos (and of course the TA series as well), with progressively larger turbine wheels that provide less backpressure, more power, and more lag. So far, the GT61 is only available together with a GT350 turbine, in 70 and 76 trim, in the small shaft format (the 70 trim might not be available with the Precision 3 bolt housing but I'm sure everyone will want the 76 trim anyway). That makes it most comparable to a PTE52 (60-1 and GT350 76 trim). Price is $675 with no elbow or actuator, with the standard TE compressor cover (actually a TO4E 3" inlet 2" outlet cover), and with the larger TO4S 4" inlet 2.5" outlet cover for an additional $100. The GT67 wheel is available with three different turbines. All of these are large shaft turbos, and cost $1075 with the TO4E compressor housing and $1175 with the TO4S housing. The smallest uses the TO4 69 trim turbine (inducer diameter 2.92", exducer diameter 2.42"), the same turbine used in the PTE53, PTE54, and TE61 turbos. None of the common TR turbos uses this combination of such a large compressor and small turbine so there doesn't seem to be anything to compare it to. The next one uses the TO4 P trim turbine, and the last one uses the new GT-Q trim turbine. The best comparison for the P trim version is the Precision PT66, Limit Engineering TE-45A, and Turbonetics T66 (with P trim) which all use the T66 compressor wheel and P trim turbine. According to Joe the GT67 will outspool these and make a few more hp. From what I've seen, most people don't step up to a Q trim turbine until the compressor is 72 mm or larger, but if the GT-Q can really outspool the old P trim then the GT67 Q may turn out to be the most popular of the three - time will tell.
Well, that's all the info I have. Hopefully Precision will get their website updated soon with this info and with hp/et estimates for the various configurations, and more compressor maps.
Joe and John, please correct anything I've misstated.
Ever since Garrett announced these, we have all been waiting and waiting for more info. I spent some time on the phone with Joe Lubrant of Precision and wanted to pass on what I've learned as of July, 2003. First, Garrett is selling complete turbos for other cars but they do not have a 3-bolt turbine housing so they aren't selling them for our cars yet. Precision is working on adapting their turbine housing to the new center section and will be supplying that to Garrett when it is ready, which may be several more months. At that point vendors will be able to order complete units with either plain bearings or the double ball bearings, instead of assembling them themselves, if they so choose. For now, Precision (and others) are buying a few different sizes of the new GT wheels and using them in their current turbos, with the same housings and center sections we've seen for the last several years. This means that you most likely won't be able to upgrade a current "GT" turbo to a true ball bearing GT turbo, since only the wheels would carry over but not the backing plates, center section, or housings (Joe didn't say this explicitly; this is my summary of several things he did say). The wheels are lighter than the corresponding old wheels for better spoolup, and are more efficient. In Garrett's terminology, wheels are specified by their inducer and exducer diameters, where the inducer part is where air or exhaust enters. So, on the turbine side the inducer diameter is larger than the exducer diameter, and this is reversed on the compressor side. If you take the square of the ratio of the smaller diameter to the larger diameter, times 100, you get the "trim". This is useful if you are comparing a series of wheels with one diameter fixed, for example the exducer diameter on a set of compressor wheels (the outer, larger diameter, so they all fit the same compressor housing), since if everything else is held constant the airflow should be proportional to the trim. For example, for the 60-1 compressor wheel used in the TE60 (and others), the inducer diameter is 2.324" and the exducer diameter is 3.000" so the trim is (2.324/3.000)^2 * 100 = 60. Or you can just think of the trim as another arbitrary part of the name of a particular wheel
. Manufacturers also use names for the trim, when they are changing both diameters at the same time. Best known examples of this are the TO4 series P trim (inducer diameter 2.922", exducer diameter 2.544", so 76 trim) and the Q trim (inducer diameter 3.111", exducer diameter 2.693", so 75 trim) turbine wheels (yes, there are also N (inducer diameter 2.922", exducer diameter 2.071", so 50 trim) and O (inducer diameter 2.922", exducer diameter 2.296", so 62 trim) trims, but they don't seem to be as useful as other choices in TR turbos).The first GT wheel that was available in turbos for the TRs was the GT350 turbine wheel, used in the PT 51 (70 trim) and PT52 (76 trim) that have been available for about three years now. The only other GT turbine wheel that I've heard mentioned is the GT-Q Q trim, with the same dimensions as the old Q trim (2.69/3.11") but lighter and with higher efficiency so it should make more power than the old Q trim and spool approximately as fast as the old P trim.
On the compressor side the first two wheels out are the GT61 (inducer diameter 2.416", exducer diameter 3.227", 56 trim) and the GT67 (inducer diameter 2.620", exducer diameter 3.310", 63 trim). The compressor map for the GT61 is available from Precision (http://www.precisionte.com/sportcompact/Maps/SC61.pdf). Comparing this to the map for the old 60-1 wheel (http://64.225.76.178/catalog/compmaps/fig9.html, among others), the GT61 flows about the same maximum amount of air, enough for about 600 hp max (my estimate from the map, not a spec from Joe), but the GT61 is more efficient and maintains this efficiency to much higher pressure ratios (to at least 33 psi vs. about 27 psi at 50 lbs/min airflow or about 500 hp). This means that on a stock headed stock intercooled engine that needs to run lots of boost, the GT61 will make more power. With ported heads or GN1s where more hp can be made at lower boost, the GT61 still wins due to the better efficiency but the difference will be smaller. So far I haven't found a map for the GT67 but Joe described it as similar to the old T66 but with higher efficiency and again, a much larger efficient region extending to well over 30 psi boost. I've heard a GT70 wheel mentioned but have no info on it. There is also a 66 mm TO4R wheel available, which is also lighter than the old T66 wheel and more efficient at lower pressure ratios. It would be interesting to compare the maps for the GT67, T66, and TO4R 66 mm when they are all available.
Now, on to complete turbos available from Precision (I'm sure the other vendors can assemble comparable units but I have pricing from Precision). A good summary of current non-GT turbos is available at http://www.gnttype.org/techarea/turbo/turbowheels.html. The old 60-1 compressor wheel is used in the TE60, PTE52, PTE54, and TE61 turbos (and of course the TA series as well), with progressively larger turbine wheels that provide less backpressure, more power, and more lag. So far, the GT61 is only available together with a GT350 turbine, in 70 and 76 trim, in the small shaft format (the 70 trim might not be available with the Precision 3 bolt housing but I'm sure everyone will want the 76 trim anyway). That makes it most comparable to a PTE52 (60-1 and GT350 76 trim). Price is $675 with no elbow or actuator, with the standard TE compressor cover (actually a TO4E 3" inlet 2" outlet cover), and with the larger TO4S 4" inlet 2.5" outlet cover for an additional $100. The GT67 wheel is available with three different turbines. All of these are large shaft turbos, and cost $1075 with the TO4E compressor housing and $1175 with the TO4S housing. The smallest uses the TO4 69 trim turbine (inducer diameter 2.92", exducer diameter 2.42"), the same turbine used in the PTE53, PTE54, and TE61 turbos. None of the common TR turbos uses this combination of such a large compressor and small turbine so there doesn't seem to be anything to compare it to. The next one uses the TO4 P trim turbine, and the last one uses the new GT-Q trim turbine. The best comparison for the P trim version is the Precision PT66, Limit Engineering TE-45A, and Turbonetics T66 (with P trim) which all use the T66 compressor wheel and P trim turbine. According to Joe the GT67 will outspool these and make a few more hp. From what I've seen, most people don't step up to a Q trim turbine until the compressor is 72 mm or larger, but if the GT-Q can really outspool the old P trim then the GT67 Q may turn out to be the most popular of the three - time will tell.
Well, that's all the info I have. Hopefully Precision will get their website updated soon with this info and with hp/et estimates for the various configurations, and more compressor maps.
Joe and John, please correct anything I've misstated.
