GTQ vs. HPQ and 70 vs. 76 compressor

[Robert Wilson]

Any real difference in power potential between a 76GTQ versus a 76HPQ in a 3 bolt turbo?

Also, with the TSM guys running 148~150MPH now with a 70~71mm compressor, is there really any gain in going up to a 76 compressor in a 3 bolt turbo?

The turbo would be for the following engine:
274 CID
about 9.5: 1 compression
T/A heads
23X- 23X solid roller
3600 lb weight
400 trans with brake

 

[Robert Wilson]

Anybody????

 

[d90dan]

I think most go 4-bolt when going bigger then a 70.

Nice combo, how fast are you looking to go?

 

[Robert Wilson]

I am wanting to get things sorted out with a 3 bolt turbo and then later step up to a 4 bolt. Looking for 9.40s with the 3 bolt.

 

[steve hughes]

Robert i have ran as fast with a 240" 109 with a 70 HPQ as i did with my 260" stage motor with a 76 GTQ. The 70 seems to me to be a better turbo.

 

[Robert Wilson]

Robert i have ran as fast with a 240" 109 with a 70 HPQ as i did with my 260" stage motor with a 76 GTQ. The 70 seems to me to be a better turbo.

Steve,
Thanks for the reply. Your TSM combo performance is one of the reasons I am asking these questions.

 

[bison]

I am wanting to get things sorted out with a 3 bolt turbo and then later step up to a 4 bolt. Looking for 9.40s with the 3 bolt.

This makes little sense unless you plan on running in TSM. Id go right to the tangential 4 bolt and avoid the wasted time and loss of power with the 3 bolt setup. Imo the 76 with a 3 bolt is a waste. Backpressure will be virtually the same at a given hp because there is no gain in flow on the exhaust side. Ive seen the 76 with an old Q not GTQ with a POS on center 4 bolt(which is probably worse flowing than a 3 bolt GTQ) go 137mph on 8.0:1 274ci stage 2 at 3800lbs running 20 psi with a 13% converter slip. With todays tech GTQ/HPQ, tangential 4 bolt, and PTC converter the car would have run 141-142mph at the same boost level. Id suspect it would approach 147-148mph with 30psi. Backpressure would be climbing fast over 145mph though.

 

[RUQWKNF]

I completely agree with what bison just said.
You reach a point with the 3-bolt housing 76 that is doesn't perform to it's full potential due to back pressure losses. When it comes to the 76 compressor wheel, you really need a T4 Tangential .81 or .96 A/R housing to reach it's full potential. .81 on a journal bearing turbo is the largest I'd go on a stage motor that wants quick spool up on the street. .96 if it was a dual ball bearing chra tho. A similar turbo is the GT4276R for TSL class, but it has larger compressor cover and turbine housing. It's available from PTE. Major plumbing differences between this turbo and a PT76 GTQ (HPQ) with a 3-bolt turbine housing tho.

In the Buick configuration, I would always spec the 74 model vs the 76, as the 74 turbo showed to make more useable power throughout the rpm band vs the 76 compressor, which was a peaky turbo. (IOW, it made slightly more power at higher rpms vs the 74 wheel) If you are building this combo from scratch, and are wanting to run it in a class such as TSE, then yes, you are limited to the 76 3-bolt version. But if you're not class racing, I'd start fresh with a T4 Tangential configuration from the get go. Otherwise you're breaking one of the GoFastitis rules and will be spending twice.
Just my O2's worth.

Patrick

 

[Blazer406]

Just my O2's worth.

Patrick

Patrick... your 2 cents are always worth much more. I am glad you are around to help out here......

Thanks.

 

[Robert Wilson]

I completely agree with what bison just said.
You reach a point with the 3-bolt housing 76 that is doesn't perform to it's full potential due to back pressure losses. When it comes to the 76 compressor wheel, you really need a T4 Tangential .81 or .96 A/R housing to reach it's full potential. .81 on a journal bearing turbo is the largest I'd go on a stage motor that wants quick spool up on the street. .96 if it was a dual ball bearing chra tho. A similar turbo is the GT4276R for TSL class, but it has larger compressor cover and turbine housing. It's available from PTE. Major plumbing differences between this turbo and a PT76 GTQ (HPQ) with a 3-bolt turbine housing tho.

In the Buick configuration, I would always spec the 74 model vs the 76, as the 74 turbo showed to make more useable power throughout the rpm band vs the 76 compressor, which was a peaky turbo. (IOW, it made slightly more power at higher rpms vs the 74 wheel) If you are building this combo from scratch, and are wanting to run it in a class such as TSE, then yes, you are limited to the 76 3-bolt version. But if you're not class racing, I'd start fresh with a T4 Tangential configuration from the get go. Otherwise you're breaking one of the GoFastitis rules and will be spending twice.
Just my O2's worth.

Patrick

Patrick,
Thanks for the input... I also sent you a PM.

 

[et10sec]

Gtq 76

question, i have a gtq 76(62 housing) on a stage 2, going to have it checked out by limit, could i up grade to a .82 housing and still spool of the foot brake?

 

[RUQWKNF]

et10sec,
What converter and stall are you running now?

Also, what is a 62 housing?

Did you mean a .63 A/R turbine housing? Being a GT-Q turbine wheel 76 turbo, the next steup in turbine housing would be a .85 A/R PTE housing. Which Precision might not have anymore left at this point. With the GT-Q turbine wheel being displaced by the HPQ turbine wheel, I'd be willing to bet that production has switched gears over for that new housing. You're best bet would be to call PTE and ask them if they have any THB5-80 turbine housings left on the shelf.
I doubt Limit would have any left either, but you never know.
Thanks guys, I try to help when I can.
HTH

Patrick

 

[et10sec]

housing

hi there, thanks for the advise, i was using a art carr, ,non lock up, 3800, it worked ok, now i have the new one from dusty, 3800 n/l, so, its possible to spool this 76/with a bigger housing of the foot brake, any one try this? thanks

 

[et10sec]

gtq 76

so, there is no one using a GTQ76 with the foot brake??

 

[et10sec]

Gtq76

ttt