Moving up from a GTQ70, could use some help

[Nashty]

I think I'm making around 850 flywheel hp with my GTQ70 (T4 turbine housing).

I want to make life a little easier on the motor and have a bit more upside, not crazy power, just maybe another 100hp or so.

I'm looking to move to a BB turbo. My thinking from some research is a 74 GTS BB turbo w .81 A/R T4 housing.

Right now, I have a very good but tight convertor. I'm addressing that but DO NOT want to induce more lag. Would moving to an S trim wheel be detrimental to spool? I'm worried about moving up larger and getting more lag. I'd rather have the convertor tight than a big turbo.

Will the 74GTSBB spool at least as well as my current 70GTQ non BB?

Would a Q trim wheel choke the motor too much at that power level? OR - will an S trim wheel cause it to lag too much?

TIA - Roger

 

[RUQWKNF]

Couple of questions first.

1. CI size of the motor this is on?

231-235 size will see more lag with a GTS turbine wheel.
248 and up won't be as bad and will free up some back pressure. But it is highly recommended to run at least a 3.5" downpipe vs a 3" with this turbine wheel. It needs to breath.

2. What boost do you plan on running?

19-23psi you won't see that much gain over the 70 wheel, but 25-30 you will see close to 100 more, especially if you go with a GTS turbine wheel.


3. What converter do you have?

Non lock up 9" 4000 stall? Or tight lock up 9.5" ? This will have a dramatic effect going from GT-Q to GT-S using the same Tangential .81 housing.

4. Are you willing to change your downpipe and compressor cover inlet pipe and discharge flange?

If so, you have another option, and that would be the GT4276R. It comes with a larger compressor cover and a more efficient turbine housing that uses a larger downpipe. This turbo in non ball bearing with the 1.28 A/R housing is the standard turbo that most of the guys in TSL class ran last year with their Stage II motors.
Here's a pic of Louie Lopez's car from last year with a GT42 turbo.

If you don't want to change anything, are planning on running high boost, and have a decent converter on a + size CI motor, then the PT74 GT-S dual ball bearing with a .81 Tangential housing would be the one I would go with.
Hope this helps a little.

Patrick

 

[Nashty]

1. CI size of the motor this is on?

231-235 size will see more lag with a GTS turbine wheel.
248 and up won't be as bad and will free up some back pressure. But it is highly recommended to run at least a 3.5" downpipe vs a 3" with this turbine wheel. It needs to breath.

235 It's a 3" V-band that goes to 3.5" after about an inch.

2. What boost do you plan on running?

19-23psi you won't see that much gain over the 70 wheel, but 25-30 you will see close to 100 more, especially if you go with a GTS turbine wheel.

I'd like to keep it under 27 but would like to make lots of power around 24

3. What converter do you have?

Non lock up 9" 4000 stall? Or tight lock up 9.5" ? This will have a dramatic effect going from GT-Q to GT-S using the same Tangential .81 housing.

Chance 10.5 ProMod, probably around 2800-3000 stall

4. Are you willing to change your downpipe and compressor cover inlet pipe and discharge flange?

If so, you have another option, and that would be the GT4276R. It comes with a larger compressor cover and a more efficient turbine housing that uses a larger downpipe. This turbo in non ball bearing with the 1.28 A/R housing is the standard turbo that most of the guys in TSL class ran last year with their Stage II motors.

If you don't want to change anything, are planning on running high boost, and have a decent converter on a + size CI motor, then the PT74 GT-S dual ball bearing with a .81 Tangential housing would be the one I would go with.
Hope this helps a little.

Patrick

Thanks Patrick - you're helpful as always.

I'd like a 4276R but it just won't fit unless I put a hoodscoop on the car to cover the turbo hole. Do a major rework of the headers. Come up with a completely different air intake setup and make a new downpipe to fit my car, which was hard enough with 3.5" pipe.

Do I have any other options out there? What about a 72GTQ bb turbo? Will that open up much more potential?

I have a great IC, at Indy, I logged 40º intake temps when it was ~80's outside. That was at the top end of a 155 pass. (Liquid IC's are great )

 

[RUQWKNF]

Honestly bro, you won't see enough of a gain going from a 70 GT-Q non bb to a 72 GT-Q dbb. Maybe 10-15hp at best at the same boost level. And to me, that little bit of gain wouldn't warrant the costs.
I'm assuming this in on a Stage II motor right?

I personally would go with a 74 GTS with the dual bb and the .81 A/R Tan housing. To me, this would be the best choice for spool up and extra power. As well as being the closest thing to a GT4202R but with normal H compressor cover and normal T4 Tangential housing.
The 74 GTS is rated to support up to 1050 fwhp, which is 200 more than your current turbo. Eventho the turbine wheel is larger and adds more weight to the rotating assembly, this would be offset with the dual ball bearing chra. Don't forget the water coolant lines. If you no longer run a factory style intake (which running 155 I would imagine not) and don't have the factory water pipes, they offer a universal water coolant line kit so you can plumb your own lines. Plus it's a lot cheeper than the Buick specific water coolant line kit.
The 74 GTS dbb would be a very smart move as far as an upgrade goes.
HTH

Patrick

 

[Nashty]

For some reason, I just can't get my mind convinced that an S trim combined with a bigger comp wheel will spool quicker than my 70 Q trim.

Can I try one out before spending $2500 on a turbo?

I'll have to rig up water cooling but that's not too big of an issue for me. Can't I just buy the fittings that go into the turbo (for the water) anywhere? I hate to spend $75 on basically the two fittings I'll end up using anyway. What size are they? I presume they use a sealing washer vs. an O ring.

 

[RUQWKNF]

Here ya go.
These guys offer three different fitting methods.

GT BB Install Parts: atpturbo.com

The water coolant passages are 14mm.

HTH

Patrick

 

[norbs]

I wonder how much power you could make if you upgrade your gtq to a GTS trim and leave the 70 compressor side alone?

 

[RUQWKNF]

Well, they say 25hp difference, but I've heard from users that it was more like 50.

Patrick