# Gtx3071r



## suffocatemymind (Dec 10, 2007)

Hello 2.5 forum,

I'm a 1.8T guy but I've been browsing this forum for a few months since my girlfriend got a MK5 2.5. I've always thought that this would be a sweet motor to turbocharge and after doing some reading...it is. A 20v with .7 more liters?! Sign me up.

I did, however, notice one thing "off" (in my mind) and that's turbo selection. A lot of you 2.5T guys/gals seem to be using relatively lazy turbos at lower PR's to get the power that you're making.

Case and point: have any of you considered using a smaller turbo at higher PR's? Some 1.8T folk have been messing with the new, high-flowing GTX turbos and after some math crunching, the GTX3071R @ 22-23psi (by ~3100 RPMs :thumbup on a 2.5 engine can make 500 BHP. That's awesome. That's a lot of torque to play with. I'll have to pull up a compressor map with data points later...

Discuss opcorn:


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## biggerbigben (Jan 21, 2004)

I've gone for a GTX3076r with a .63 tial... I worked out that I could achieve similar to what you've quoted, perhaps a little later in the rev range. Some boost figures done on a 2.5L subaru motor.


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## suffocatemymind (Dec 10, 2007)

biggerbigben said:


> I've gone for a GTX3076r with a .63 tial... I worked out that I could achieve similar to what you've quoted, perhaps a little later in the rev range. Some boost figures done on a 2.5L subaru motor.


That turbo seems like another decent choice! Check out the spool on this, 22psi from 3000-7200RPMs, flowing ~55 lbs/min aka ~550bhp...sounds like the perfect match up IMO.









2.5T guys...comments?


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## suffocatemymind (Dec 10, 2007)

No one? Everyone is totally 100% content with lag and less torque? Don't just say "ah well wheel spin blah blah" ...LSD + some gummy tires will cure that.

Haha  COME ON!


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## biggerbigben (Jan 21, 2004)

Not many on this forum have gone turbo yet and even less have a GTX... on their 2.5 

Think it makes perfect sense but even I'm not going to have mine anywhere near a dyno anytime soon to share the figures! Come back in a couple of years and there might be a view dyno graphs posted!


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## suffocatemymind (Dec 10, 2007)

Well I see that, but there are a decent number of 2.5T guys and they all seem to be running lazy-ish turbos at low boost levels. I'm asking them to chime in here, and for future 2.5T users to be aware of their options. And in my opinion, better options. No dyno graphs necessary - I've seen the ones that are in the forum (which is mainly why I started this thread).

United Motorsports - I see you have turbo tunes with this engine. How feasible would it be to tune for a smaller turbo at higher boost (GTX3071R @ 22psi)?

C2 - have you guys considered a quicker-spooling turbo in your kits? Pardon my ignorance if you already do.

Speak up 2.5T guys!


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## thygreyt (Jun 7, 2009)

suffocatemymind said:


> Well I see that, but there are a decent number of 2.5T guys and they all seem to be running lazy-ish turbos at low boost levels. I'm asking them to chime in here, and for future 2.5T users to be aware of their options. And in my opinion, better options. No dyno graphs necessary - I've seen the ones that are in the forum (which is mainly why I started this thread).
> 
> United Motorsports - I see you have turbo tunes with this engine. How feasible would it be to tune for a smaller turbo at higher boost (GTX3071R @ 22psi)?
> 
> ...


i have a 5858 pte... 

um... idk, i have tried smaller turbos (5457) .63 AR....

The 3071 is a 5360 in PTE terms... anyways, sure it a good turbo... but in my experience is an agressive set up... you are always spooling and boosting. You have next to no control on the compression/spooling. It KILLS fuel economy.

But on the other side, i do agree: the car moves much more easily because of the extra down torque, and it suffers on the top when copmared to the .82 AR

in the end, its up to you... i like my set up... and either way, on 550cc you will run out of injectors at around 14-15 psi.


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## suffocatemymind (Dec 10, 2007)

thygreyt said:


> i have a 5858 pte...
> 
> um... idk, i have tried smaller turbos (5457) .63 AR....
> 
> ...


Now that's what I wanna hear, thanks for the feedback. The GTX series, while billet, spool a tad slower than their non-X counterparts - but flow more and have increased efficiency. I really wonder how this turbo would pair with the 2.5 engine.

That's another thing - I feel like the lack of bigger injector tunes are holding people back a bit. 

Curious: when do you reach 15psi?


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## TrillyPop (Jan 27, 2010)

My car for the last 6 months has had a pt5457 and 550cc injectors running at 15psi. It's a billet turbo. I really like the spool characteristics of it. It starts spooling at 1800psi, reaches full 15psi at about 3100rpm, and holds that until redline at ~7500rpm. Sure, it doesn't flow as much as one with a bigger turbine, but I have found it to mate very well with the 2.5L. I like the power down low, and being able to build speed very quickly even when staying in 6th gear on the highway.

My car is currently in the shop for upgrades - SRI, RS4 fuel pump, return fuel system, and bigger injectors (I think 900 or 1200cc, still to be decided). So my plan is to push the 5457 up to high boost (20-25psi) and see if it can hold boost and what kind of power it makes. If it doesn't make enough power, I'll likely move up to a 5862 (which is "laggy" per your description OP).

EDIT: I think one of the biggest reasons that we tend to run slightly bigger/"more laggy" turbos is that the stock 2.5l can't safely handle very much boost. In totally stock form it's about 8-10psi and with an SRI it's maybe 14-15psi. And while we all know that there was once a turbo Rabbit that made 400whp on a stock motor for a dyno pull, I doubt any of the big tuners would advise running a setup like that. So to compensate for the boost limitations, we tend to use bigger turbos that move more air to make up the power that way. Sure, you lose some low-end, but you make more on the top end.


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## thygreyt (Jun 7, 2009)

i guess its also down to taste..

i could go with a .63 AR instead of the .82, and that would mean a good difference in the spooling... but i like the .82 because its more refined, OEMish and smooth. Additionally, i have full control of when and how the boost comes in.

the way i see it: i can have ~400 hp and maintain a good ~28 mpg.. all good.


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## TrillyPop (Jan 27, 2010)

thygreyt said:


> Additionally, i have full control of when and how the boost comes in.


So does anyone with a UM tune...boost by throttle position. If there is too much boost/power at low rpm, you need wider/stickier tires  I know what you're trying to say about the boost coming on smother, but that's really just turbo lag.


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## suffocatemymind (Dec 10, 2007)

TrillyPop said:


> So does anyone with a UM tune...boost by throttle position. If there is too much boost/power at low rpm, you need wider/stickier tires  I know what you're trying to say about the boost coming on smother, but that's really just turbo lag.


Bingo


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## thygreyt (Jun 7, 2009)

TrillyPop said:


> So does anyone with a UM tune...boost by throttle position. If there is too much boost/power at low rpm, you need wider/stickier tires  I know what you're trying to say about the boost coming on smother, but that's really just turbo lag.


lol, i know... but the range of the NA mode is wider on the laggier set up... plus being on boost all the time is fun, but it eats fuel.

i get 27-30 mpg on the .82 and 23-26 on the .63 AR... since this is my daily driver, and i drive ~25k a year, mpg is important.


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## TrillyPop (Jan 27, 2010)

Like I said, though, the biggest limitation for most 2.5T guys is that the engine can't handle a ton boost in stock form. Faced with this limitation, most guys opt to have more power up top, all the way up to 7800rpm where the 2.5l shines, rather than to sacrifice that for low-end torque. You know? I agree, running 25psi on a 3076 would be awesome, but most can't do it. They would be limited to 14psi and then with that turbo would make less power than they would with a 5557 or 5858. 

You should do it though 

IMO the .63ar is perfect for the 2.5l...we'll see what the 5457 can do at 20+psi.


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## suffocatemymind (Dec 10, 2007)

TrillyPop said:


> Like I said, though, the biggest limitation for most 2.5T guys is that the engine can't handle a ton boost in stock form. Faced with this limitation, most guys opt to have more power up top, all the way up to 7800rpm where the 2.5l shines, rather than to sacrifice that for low-end torque. You know? I agree, running 25psi on a 3076 would be awesome, but most can't do it. They would be limited to 14psi and then with that turbo would make less power than they would with a 5557 or 5858.
> 
> You should do it though
> 
> IMO the .63ar is perfect for the 2.5l...we'll see what the 5457 can do at 20+psi.


I agree with a lot of what you said. One thing that needs to be made clear is: 25psi on a small snail is not the same as 25psi on a big snail. "X" HP requires "Y" fuel. That being said, it's easy to see why injector size isn't solely boost dependent. Bosch 550's might be near their limit with 15psi on a 5858, but they'd show the same results with a smaller turbo - say GTX3071 - at higher boost levels. More boost (usually) equals more torque. Torque x RPMs = HP. More torque at lower revs can yield the same HP as less torque at higher revs. It just seems clear to me that an engine like this with a GTX3071 will offer a huge, flat torque curve from 3000-7200 RPMs! That's wicked.

Pair that with some IE rods and call it a day. The CR is already boost-friendly. Oh and that .63 is too antsy and the .82 too lazy? Pag Parts Turbo makes a custom .72 AR v-banded exhaust housing 

I just see so much potential with this engine...once it's starts adapting the proven 1.8T tech, ha watch out. This is the 20v I wish I had. I just need to buy one haha


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## mldouthi (Jun 26, 2010)

suffocatemymind said:


> I agree with a lot of what you said. One thing that needs to be made clear is: 25psi on a small snail is not the same as 25psi on a big snail. "X" HP requires "Y" fuel. That being said, it's easy to see why injector size isn't solely boost dependent. Bosch 550's might be near their limit with 15psi on a 5858, but they'd show the same results with a smaller turbo - say GTX3071 - at higher boost levels. More boost (usually) equals more torque. *Torque x RPMs / 5252 = HP*. More torque at lower revs can yield the same HP as less torque at higher revs. It just seems clear to me that an engine like this with a GTX3071 will offer a huge, flat torque curve from 3000-7200 RPMs! That's wicked.
> 
> Pair that with some IE rods and call it a day. The CR is already boost-friendly. Oh and that .63 is too antsy and the .82 too lazy? Pag Parts Turbo makes a custom .72 AR v-banded exhaust housing
> 
> I just see so much potential with this engine...once it's starts adapting the proven 1.8T tech, ha watch out. This is the 20v I wish I had. I just need to buy one haha


ftfy

I dont have a turbo but like reading about it. Carry on. :wave:


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## suffocatemymind (Dec 10, 2007)

mldouthi said:


> ftfy
> 
> I dont have a turbo but like reading about it. Carry on. :wave:


I know the exact calculation, I was just making a point. 300ftlbs at 4500 RPMs is going to have less HP than 300ftlbs at 7500 RPMs - regardless of what it's divided by. But thanks for reading the actual context, and thanks for chiming in :wave:


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