4 bolt turbo equal to the 6776bb
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Get a tangential 4-bolt housing on that same turbo. Run the biggest exhaust a/r you can stand. You will need more converter for the bigger housing but id bet you would gain at least 30 hp over the best 3-bolt you could find with the same wheels in a maxed out combo.
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If it came from PTE with a part number of 6776R, and you want to run this same turbo with the ATR 4-bolt headers on your current combo, then here is the part number for the housing you will need.
TH6876A
Make sure to specify that you will need the hardware to bolt it onto your PT6776R turbo. This would be the bolts and clamps. This is a .68 A/R T4 Tangential turbine housing that will directly bolt onto your GT6776R turbo, and don't forget the undivided SS T4 gasket. Bison is correct about picking up hp in a maxed out scenario, but there's one thing to consider. You will need to have someone fabricate a v-band style downpipe for this style of turbine housing.
If you do not plan on changing your converter, then there is no need for a larger A/R than .68 on a bolt on street 109 combo. The .68 A/R T4 Tangential housing, will out flow a .85 A/R 3-bolt Buick housing. If you were to run a .81 A/R T4 Tangential housing, the power curve would be moved dramatically higher into the rev range. Even with dual ball bearings, you would need to raise the stall speed on your converter. I would spec a .68 A/R T4 Tangential housing on a street driven 231-235 ci 109 that was built with heads, cam, headers and intake. If you were building a stroker or Stage motor that will rev past 6k, then I'd spec a .81 or .96 A/R according to CI and turbo size. A .81 A/R would kill the bottom end on a stock motor with bolt ons and a tight converter. To make a .81 work on a Dual Ball Bearing turbo that was on a 231 CI motor, you would need at least a 3600 flash stall converter.
Hope this helps.
Patrick
TH6876A
Make sure to specify that you will need the hardware to bolt it onto your PT6776R turbo. This would be the bolts and clamps. This is a .68 A/R T4 Tangential turbine housing that will directly bolt onto your GT6776R turbo, and don't forget the undivided SS T4 gasket. Bison is correct about picking up hp in a maxed out scenario, but there's one thing to consider. You will need to have someone fabricate a v-band style downpipe for this style of turbine housing.
If you do not plan on changing your converter, then there is no need for a larger A/R than .68 on a bolt on street 109 combo. The .68 A/R T4 Tangential housing, will out flow a .85 A/R 3-bolt Buick housing. If you were to run a .81 A/R T4 Tangential housing, the power curve would be moved dramatically higher into the rev range. Even with dual ball bearings, you would need to raise the stall speed on your converter. I would spec a .68 A/R T4 Tangential housing on a street driven 231-235 ci 109 that was built with heads, cam, headers and intake. If you were building a stroker or Stage motor that will rev past 6k, then I'd spec a .81 or .96 A/R according to CI and turbo size. A .81 A/R would kill the bottom end on a stock motor with bolt ons and a tight converter. To make a .81 work on a Dual Ball Bearing turbo that was on a 231 CI motor, you would need at least a 3600 flash stall converter.
Hope this helps.
Patrick
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Absolutely, but just not practical.
Now, the 3-bolt Buick housing was originally a T3 design as far as the contour and internal shape of the housing is concerned. And we have pushed the 3-bolt .85 housing as far as it will go with the 76 GT-Q. Back pressure readings don't lie. This is why a lot of people are begging for a larger A/R 3-bolt housing. The design of the T4 Tangential housing is the optimal design that you want when you start trying to make over 700 flywheel hp. But the Buick community as a whole, have not embraced the fact that running a T4 four bolt setup would require custom headers and a custom downpipe. It's just not feesable when you can run a 3-bolt and the stock stuff and make your hp goals. Only the true racers who are trying to make the most hp that's possible within a given set of rules are the ones who don't mind spending the money for high hp parts. The current 3-bolt housings are just fine for stockers all the way up to 700 flywheel hp. Back pressure readings are a very good indicator of when it's time to convert to T4 4-bolt hardware.
HTH
Patrick
Now, the 3-bolt Buick housing was originally a T3 design as far as the contour and internal shape of the housing is concerned. And we have pushed the 3-bolt .85 housing as far as it will go with the 76 GT-Q. Back pressure readings don't lie. This is why a lot of people are begging for a larger A/R 3-bolt housing. The design of the T4 Tangential housing is the optimal design that you want when you start trying to make over 700 flywheel hp. But the Buick community as a whole, have not embraced the fact that running a T4 four bolt setup would require custom headers and a custom downpipe. It's just not feesable when you can run a 3-bolt and the stock stuff and make your hp goals. Only the true racers who are trying to make the most hp that's possible within a given set of rules are the ones who don't mind spending the money for high hp parts. The current 3-bolt housings are just fine for stockers all the way up to 700 flywheel hp. Back pressure readings are a very good indicator of when it's time to convert to T4 4-bolt hardware.
HTH
Patrick
Thanks Patrick that helped a lot. As far as the downpipe I already have an ATR one specifically for those headers w/ the v-band style. I got everything together headers, x-over, wastegate and downpipe. So all I need is the turbine housing and I'll be ready to go. I was already looking at the .68 a/r housing. I know I wont need any larger than that for what i'm doing. I was also going to have my converter restalled to 3200. We'll see how it works out. I plan on trying to run in an NHRA S/S or S/G class (S/S=10.90 index and S/G=9.90 index) in a full body and weight T-Type thats driven to the track.
Patrick made a bunch of great points on this topic. One other thing that could be added to the more hard core non classed TR racer that wants to go really fast is that they could run a mild shot of N2O with a turn off switch (at desired boost level) to get the turbo spooled with the really big 4 bolt a/r housings of .96 or larger on a 231ci. At this point you really need a closed loop electronic wastegate controller too. You will be able to achieve incredible pressure ratios that most would never believe if you told them. Ive heard of some really small 4 cylinder engines doing this with 4 bolt housings and nitrous to the point that the manifold pressure is higher than the exhaust pressure! This all equals huge power gains and a lot more mph with a seemingly maxed out turbo. I myself will be going to a 4 bolt set up within the next year. I just cant see choking the race ported GN1's i just got with a tiny little 3 bolt housing. Its almost a crime to do so with heads like this unless your forced to run a 3 bolt like TSM. For that matter its the same scenario running the stock ported intake with those heads too.
Patrick,
I really like/concurr with your comments about back pressure and anything north of 700hp on a 3 bolt. with my 76gtq 3 bolt, I was having to run an enormously strong wastegate spring to make more boost. anything over 22psi. Do you agree?
Seems like when I went to the GT4276, I now do not have enough wastegate flow to keep the boost down. Air seems to rather like going through the 1.15 turbine housing. I think I'm going to have to hog on the wastegate to give the valve more travel to open up more.
Make sense?
Thanks,
John
I really like/concurr with your comments about back pressure and anything north of 700hp on a 3 bolt. with my 76gtq 3 bolt, I was having to run an enormously strong wastegate spring to make more boost. anything over 22psi. Do you agree?
Seems like when I went to the GT4276, I now do not have enough wastegate flow to keep the boost down. Air seems to rather like going through the 1.15 turbine housing. I think I'm going to have to hog on the wastegate to give the valve more travel to open up more.
Make sense?
Thanks,
John
I agree that you probably need more wastegate flow. The bigger housing reduced the exhaust pressure a lot. You may want to try lighter springs in the gate first though.
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The Evo guys have to run two Tial 44mm wastegates when they run the GT4276, even on stock CI motors with less exhaust flow. In Johns case, with the back pressure being relieved, and the 50mm now not having enough travel and enough area behind the valve, more wg is needed in order to get the boost levels back down to normal levels. Depending on exactly how low you want the boost to go, it's kinda hard to say if a modified 50mm valve is going to be enough to divert the excess exhaust away from the turbine wheel to get the boost under control. Personally, I would go with a 60mm wg if you are trying to get the boost levels down in the 15-17psi range for street cruising on that combo. HKS or Tials new one should fit the bill. I personally like the standard HKS GT because of the internal size of the body around the valve gives it the most area of flow, which should move the most amount of exhaust through that 60mm hole. This also proves the old adage, the more boost you want to run, the smaller the wastegate that you need. The less boost you want too run, needs a larger wastegate.
In your case John, you could run a second wastegate on the crossover and that should help you get the boost down to pump gas levels. However, it would need to be the same style of wastegate that you already have and have the same spring and adjustment as the one already in place. Not too mention that they both would need to be hooked up in series. I have run two Deltagates in the past that were hooked up in series when I was trying to get my boost levels down on an old LT70-1 years ago. Worked great and I had an adjustment range of 14psi - 30psi without having to go to the larger wastegates, which at the time only went up to HKSs Race series 50mm.
Hope some of this helps.
Patrick
In your case John, you could run a second wastegate on the crossover and that should help you get the boost down to pump gas levels. However, it would need to be the same style of wastegate that you already have and have the same spring and adjustment as the one already in place. Not too mention that they both would need to be hooked up in series. I have run two Deltagates in the past that were hooked up in series when I was trying to get my boost levels down on an old LT70-1 years ago. Worked great and I had an adjustment range of 14psi - 30psi without having to go to the larger wastegates, which at the time only went up to HKSs Race series 50mm.
Hope some of this helps.
Patrick
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