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Discussion Starter · #1 ·
Hi Guys,

I'm hoping I could get some help from seeing what results people have had with these turbos. They are the respective models in the Garrett & Precision range. It will be going in a R32 GTR with the application for street drag.


Engine is basically

HKS 2.8 step 3
280 cams 11.25mm lift
1mm oversized and good level of porting, springs etc
PPG 5 speed

Will be running e85 and the aim is 600-650awkw (800-850awhp) I'd like to see full boost no later than 5500rpm and will be revving to 9000rpm also would prefer to not run much more than 28-34psi to achieve this.

I have a few questions I'm hoping you can answer.

1. How much later would the GTX4202r hit full boost compared to the Gtx4294r?
2. Between the equivalent Precison vs GTX model would one be more responsive by more than 100-200rpm?

3. Will the gtx4294r make 650awkw and would this be the maximum of the turbo, what boost would be needed.

4. When would you say each of these turbos would hit full boost on my RB 2.8? 5000rpm/5500rpm/6000rpm

5. What would you expect to be the difference in lag between the 1.01 rear housing and the 1.15?

6. Between a 7175/Gtx4294r & GT4202/7675 how much difference in lag due to the bigger wheel if both use the same rear housing.

7. Would any of these turbos drop off when racing due to being to large on a 2.8?

I know there are a lot of varying factors but any advice or example that you could share would greatly assist me with deciding to go Precision/Garrett and or for the 71mm size vs 76mm size.

Cheers,
 

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Which country are you in, or at least what kind of dyno will this be tuned on? 650awkw on a Dyno Dynamics is quite different to 650awkw on a Dynapack for example :) Generally speaking the Precision turbos I would expect to be noticeably more responsive, as you noted they have smaller turbine wheels - the 7175s apparently are fairly usable on 3litres. I'd say the 7175 would be the only one in that pile which would have any chance of hitting full boost near the 5000rpm mark, depending on how the dyno is run - but that is pretty speculative. While on speculative, I'd say the 7175 would be fairly noticeably nicer to drive as a road car than the others... but again once you're getting that big I'm not sure how much it really matters, depending on what you are hoping for.

To be fair, none of those turbos should have issues keeping on boost on a 2.8litre with those size cams etc - I've driven a stock stroke RB26 GTR with the exact same size cams running E85 with a T51R SPL and that had no issue with boost recovery in gears, albeit coming on full boost late (6000+rpm) initially. With launch control that becomes a non-issue, and keeping the revs up the big wheels get a lot of momentum and all is well.... the PPG box would be my concern, and I guess how usable you want it to be on the street.

Depending on the dyno you are using - even those turbos might be on the generous side. I know someone in Oz putting an FP Super94 HTA (6768 in Precision nomenclature) on an RB30DET with a reasonably build head who will be aiming for 30psi on E85, that'll be quite interesting to see power and spool but I am picking it'd do that 800+whp range on pretty much any dyno without too much stress, I am just looking forward to seeing the RB30 result to see how the hotside copes with delivering that power on moderate boost levels compared to the EVOs they are usually used on.
 

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Discussion Starter · #4 ·
Hi Lith on an Australian dyno what really begs the question is how is the 7175 more responsive than a Gtx4294r when they both have the same size wheel and same rear housing? Im more curious about when full boost is achieved as really don't want 6000rpm full boost but at the same token I'm happy with 5-5500rpm which is why I want to rule out which turbos would be outside of that range.
 

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Woops yeah you are right sorry, I kept thinking of the GT42 as a 82mm wheel (it is, but in the turbine inducer) - but it's actually 75mm exducer like the Precision... got my naming wires crossed. Ignore me on that one, I don't speed so much time looking at this size!

I guess the GTX4294R probably applies similarly, but I don't have any direct experience with them so can't say for sure. Would probably need a comparison between the GTX4294R and the PT7175 to really see how comparable they are, wouldn't want to place any bets there but would like to think that things would be really coming to life by 5500rpm with good manifolds, tuning on a good 2.8litre.

Pretty confident that both will hit your power targets quite happily. So on a Dyno Dynamics or a Mainline Oz dyno?
 

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Forgot about that one, good call - Andy :) That's not full boost or "all in" with that turbo either, though... from memory?
 

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Discussion Starter · #8 ·
Thanks RH9 actually looks pretty good in terms of response I believe looks like he'd be using a 1.01 (smallest) rear housing and doesn't look like hi boost yet.
 

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Yeah the turbo is a little restrictive if anything above 1.8 bar. I think they stopped at 2 bar as they were only using 98 octane and the motor had only done very little mileage.

I wouldn't have any hesitation using one if I had a sequential gearbox to keep the driveline reliable :)
 

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Discussion Starter · #12 ·
The White elephant was running 45psi to achieve 700awkw maxing the turbo I believe they made 600awkw around low 30s psi definitely looks like a great turbo.
 

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Yep - that's what I figured, on the boost levels you were talking it was sitting right in the power range you were aiming for on the kind of dyno and setup you have in mind so it seems like quite a good match :) The fact it can go up to 700kw if you decide to go kill mode is just a "bonus".

Would probably be my choice, lots of guys have used these on Supra street cars and even EVOs and Silvias (PJ.... ) have run them to great effect. If you think you have the cam and headwork for it the PT7285 tend to work better pound for pound as well, if boost is a concern.
 

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Discussion Starter · #14 ·
Was just wondering if it's worth going the next size up and how much laggier that would be. Ie the 7675 wonder is 4-5mm wheel size increase would equate to how much lag ie 200 or 500+ rpm laggier
 
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