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Single vs twin turbo.


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Hi there. 
 

I’ve been a long time lurker on this site and finally bought a stock standard R32 GTR. I plan to do bolt on mods that make it perform better but I want to be able to return the car to stock if needed. 
 

Big question at the moment is which turbos to go with. I was pretty set on going with -9 turbos. This is mainly based on stuff I’ve read on this forum over the last couple of years. But I liked the fact they should perform well (300awkw, would make it a very fast car by my standards) and I can keep the engine bay looking factory. 
 

The guys tuning the car think it’s silly to not go single. 
But I have the following concerns. 
1, drivetrain issues. From what I’ve read on here at 300-330awkw the driveline should be pretty safe at that level. I plan to go to a nismo clutch. At 400awkw am I pushing the factory driveline too far and should upgrade it?

2, will the car have to be cut or modified in anyway to fit the single? I don’t want to make any changes that can’t be bolted back to factory if I can avoid it. 
 

3, what turbo would you recommend? Which singles will be similarly responsive as -9 but be able to provide more kw up top?

I know the usual reaction is to mention to search these things but truthfully I’ve spent a crazy amount of time reading up on this stuff and now my wallet if finally about to start being emptied any more info would be very much appreciated. 
 

Also this is likely to be first of a few looking for help choosing parts on this build. 5AB44B0B-D1B0-461D-881A-23F2E9D95A6C.thumb.jpeg.9cb833b06fa841f8009e3e6f11acbc90.jpeg

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On 8/12/2021 at 3:38 PM, Fizurg said:

1, drivetrain issues. From what I’ve read on here at 300-330awkw the driveline should be pretty safe at that level. I plan to go to a nismo clutch. At 400awkw am I pushing the factory driveline too far and should upgrade it?

Perhaps that's not the question to ask. For any given power level the single will smack the twins senseless. More response, more area under the curve (from the single). So you could put a "smaller" single on and shoot to max it out at less than 400rwkW (say, aim for 350) and enjoy life a lot more.

On 8/12/2021 at 3:38 PM, Fizurg said:

2, will the car have to be cut or modified in anyway to fit the single? I don’t want to make any changes that can’t be bolted back to factory if I can avoid it. 

No.

On 8/12/2021 at 3:38 PM, Fizurg said:

3, what turbo would you recommend? Which singles will be similarly responsive as -9 but be able to provide more kw up top?

See 1.

First question though would be "what fuel?" You can push smaller turbos to more power using E85 than you can on 98. E85 allows higher boost, which causes higher air temps at the same compressor efficiency and pushing the boost higher usually reduces efficiency when you're aiming for the top of the compressor map.

The recommendation will be for a T3 or T4 twin scroll housing and proper divided manifold and wastegate arrangement. Have a look at the various RB25 & 26 turbo upgrade threads stickied on here to see what people are achieving. The options range from GTX3076, through GT3576 or GT3582, to G30-550 or 660, and BW EFRs like the 7670. There's a lot of size difference across those ones I've listed, and not all are available with divided housings, etc. And that's ignoring Precisions and all the off-brand stuff.

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GTX3576R Gen 2 with 1.01 divided housing, twin scroll manifold, pump as much boost as you want until it stops making power (and not worry about turbines ejecting into the exhaust area or compressor wheels smashing into housings).

Reliable, fast and fun.
 

I am biased.

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On 12/08/2021 at 6:54 PM, GTSBoy said:

Perhaps that's not the question to ask. For any given power level the single will smack the twins senseless. More response, more area under the curve (from the single). So you could put a "smaller" single on and shoot to max it out at less than 400rwkW (say, aim for 350) and enjoy life a lot more.

No.

See 1.

First question though would be "what fuel?" You can push smaller turbos to more power using E85 than you can on 98. E85 allows higher boost, which causes higher air temps at the same compressor efficiency and pushing the boost higher usually reduces efficiency when you're aiming for the top of the compressor map.

The recommendation will be for a T3 or T4 twin scroll housing and proper divided manifold and wastegate arrangement. Have a look at the various RB25 & 26 turbo upgrade threads stickied on here to see what people are achieving. The options range from GTX3076, through GT3576 or GT3582, to G30-550 or 660, and BW EFRs like the 7670. There's a lot of size difference across those ones I've listed, and not all are available with divided housings, etc. And that's ignoring Precisions and all the off-brand stuff.

Cheers for the great response. After spending countless hours looking for twin turbo stuff I’m pretty new to anything to do with single turbo set ups. 
 

The 400rwkw I sort of just plucked out of the air. But anything in the 350-400 range would be amazing. At these power levels are driveline upgrades needed?
 

The gas will be 98. It’s wildly available here unlike E85. There is also a new fuel supplier offering 100 octane petrol but i haven’t looked into it. 
 

Looks like I will have to reacquaint myself with the dyno thread again. 

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On 12/08/2021 at 7:05 PM, Dose Pipe Sutututu said:

GTX3576R Gen 2 with 1.01 divided housing, twin scroll manifold, pump as much boost as you want until it stops making power (and not worry about turbines ejecting into the exhaust area or compressor wheels smashing into housings).

Reliable, fast and fun.
 

I am biased.

What were your results with this turbo, if you don’t mind me asking?

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Single turbos make very little sense for a GTR these days (ie, since they became a mega expensive collector's car)

If you want a performance car with 400kw there are better choices built in the last 30 years.

If you want a GTR because of what they were when they were made back in the day, twin turbos are what the factory chose. For road use, there is no practical difference between 300, 400 or 600kw, they all have too much power to keep your foot down for more than about 3 seconds.

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@Duncan is being a grumpy old man. He's not wrong, but if you want to get more power and make it nicer to drive, put a single on it.

Having seen your intro thread now though, I would suggest perhaps not bastardising the car.

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Cheers guys. I think you can see the dilemma. For performance, a single is the obvious choice. But I feel like the twins should be enough to make the car more than enough fun for me and if I can keep it looking original there is an appeal to me for that. 
with the twins I can leave the engine bay looking stock and it would almost be a bit of a sleeper. Not that a GTR is a very good base for a sleeper. 

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The twins have SOME merit because you can say they were made specifically by Garrett as upgrades for this specific car (I don't mean factory upgrades, but turbos made specifically for the RB26).

To use the car as an actual performance car for actual performance, a smaller Garrett G series as a single would be absolutely awesome, and be physically small and absolutely give you lovely clearance to everything and more than enough power without blowing things to smithereens.

You wouldn't pick any other Garrett turbo in 2021 - They are their best product, though many other products of the past would still be considered a big upgrade to stock.

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On 12/08/2021 at 5:44 PM, Fizurg said:

What were your results with this turbo, if you don’t mind me asking?

I have (I did have) a RB25DET NEO, so it has less displacement than a RB26. I was able to get 407kW at the rear wheels (with a cracked FMIC and sky high intake air temps). I did put on a better FMIC but sadly the motor imploded due to oil starvation issues.

 

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GTX3576R gen2 T3 open scroll RB26, stock bottom end, average compression with reco head and bits n pieces up top, cams etc. 440 odd kw at the hubs.

Don't have a boost gauge apart from the 34 GTR MFD, but on the Haltech, E60% ethanol in winter, 152.2 Kpa at 3615rpm.

Screen Shot 2021-07-16 at 3.46.14 pm.png

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On 13/08/2021 at 12:26 PM, djvoodoo said:

GTX3576R gen2 T3 open scroll RB26, stock bottom end, average compression with reco head and bits n pieces up top, cams etc. 440 odd kw at the hubs.

Don't have a boost gauge apart from the 34 GTR MFD, but on the Haltech, E60% ethanol in winter, 152.2 Kpa at 3615rpm.

Screen Shot 2021-07-16 at 3.46.14 pm.png

Sex, comes on earlier than the stock twins

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After talking to the guy who’s going to tune it and the guy doing the work I’ve been convinced to go for a 8374. It’s way more power than I expected to get but reading up it seems like a pretty exciting option. 
I’m halfway through the 130 odd pages in the EFR thread and am amazed at the results. There seems to be a feeling that the IWG options aren’t as good as the EWG ones. But I’m guessing there would be some cost savings with the IWG especially vs a twin external wastegate set up. Does anyone have any experience with the 8374 IWG vs EWG. Is there cost savings? Is there performance sacrifices? Is a twin wastegate setup needed for a twin scroll 8374?

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On 8/17/2021 at 6:02 PM, Fizurg said:

After talking to the guy who’s going to tune it and the guy doing the work I’ve been convinced to go for a 8374. It’s way more power than I expected to get but reading up it seems like a pretty exciting option. 
I’m halfway through the 130 odd pages in the EFR thread and am amazed at the results. There seems to be a feeling that the IWG options aren’t as good as the EWG ones. But I’m guessing there would be some cost savings with the IWG especially vs a twin external wastegate set up. Does anyone have any experience with the 8374 IWG vs EWG. Is there cost savings? Is there performance sacrifices? Is a twin wastegate setup needed for a twin scroll 8374?

If you’re going to be spending that much on a turbo you may aswell just do it properly and go the full twin external gate option.

you would hate to get all the way to the end and always have that little bit or regret/ wonder what if, if I had gone the other option. Just more cost effective to do it properly in one hit

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On 17/08/2021 at 8:27 PM, UWISSH! said:

If you’re going to be spending that much on a turbo you may aswell just do it properly and go the full twin external gate option.

you would hate to get all the way to the end and always have that little bit or regret/ wonder what if, if I had gone the other option. Just more cost effective to do it properly in one hit

Yeah, that makes sure. I think part of me was hoping people on here would say not to worry about it. That the 10 extra kw aren’t worth the effort. Sadly it seems that’s not the case haha. 

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On 8/17/2021 at 8:11 PM, Fizurg said:

Yeah, that makes sure. I think part of me was hoping people on here would say not to worry about it. That the 10 extra kw aren’t worth the effort. Sadly it seems that’s not the case haha. 

The real difference isn't "Single vs Twin" its the fact that for any kind of sensible power figure, Single turbo development has kept on going instead of the direct bolt on twins in the 90's.

You could use two of these new, modern turbos, for approximately the same result as a single of the same total size of two modern ones combined, but as that is more expensive, and more complicated, and that generally turbos get more efficient as they get larger..... people don't choose to do this.

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On 17/08/2021 at 10:19 PM, Kinkstaah said:

The real difference isn't "Single vs Twin" its the fact that for any kind of sensible power figure, Single turbo development has kept on going instead of the direct bolt on twins in the 90's.

You could use two of these new, modern turbos, for approximately the same result as a single of the same total size of two modern ones combined, but as that is more expensive, and more complicated, and that generally turbos get more efficient as they get larger..... people don't choose to do this.

Yeah, if I stayed with twins it would have been to save money and keep the engine bay looking stock. The EFR twin set ups look really cool but out of budget and don’t seem to make sense compared to running one bigger one. Pretty cool for show cars and things like that though. 

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To me the interesting test would be something like EFR7064 single vs whatever flavor of the day bolt-on twin turbo with comparable power output, assuming you added whatever you needed to try and fix some of the more blatant issues like the really awful twin turbo merge pipe, etc. I have a feeling it would be the EFR7064 but how far off with the stock-ish twins be?

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On 18/08/2021 at 10:45 AM, joshuaho96 said:

To me the interesting test would be something like EFR7064 single vs whatever flavor of the day bolt-on twin turbo with comparable power output, assuming you added whatever you needed to try and fix some of the more blatant issues like the really awful twin turbo merge pipe, etc. I have a feeling it would be the EFR7064 but how far off with the stock-ish twins be?

I could be wrong with the turbo number but the tuner did mention going down to a 7xxx turbo which would beat -7 twins in every way. But he said it’s always better to go one size up as most people end up wishing they had. 

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