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What turbo for my VR6/R32?


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Can't believe there isn't a "which turbo?" thread as a sticky. As I'm always asked this by builders and as it always crops up here I will give my 2p's worth! .

First of all, this is just a basic guide for VR/R specific "what turbo's?", specific info on turbo speccing I would suggest reading things like this;

https://turbobygarrett.com/turbobygarrett/basic

and going through all their guides plus many more threads on the net. This is probably for noobs then who don't want to learn that!

I would estimate that around 90% of owners that come to me are usually looking for around the 400-450hp mark. Should you get a turbo that flows that? No! Technically speaking, say a V6 4Motion runs 200lb/ft of torque, then a highly efficient V6, 100% efficient -  running a bar of boost - i.e. you have compressed the ambient air - outside air - to double it's original density - ambient pressure which is 14.7 psi, pounds per square inch or 1013mbar is what you feel every day just walking about - is compressed by the turbo - so would run 400lb/ft or 400hp thoretically at double the stock ambient pressure..

Although it would show 1 bar of boost on  your gauge, you have essentially taken normal air - a density of 14.7 psi, and squashed it to half it's size, subsequently making a square inch twice as dense - or 29.4psi absolute pressure - i.e 14.7+14.7. That is basically what a turbo does - compresses air!

So, theoretically speaking, if you double the air density, you're doubling the output - 400lb/ft in that example. However, there are many factors as to why your car doesn't achieve that! Efficiency is the reason. There are a number of things which make your car less efficient.

Most of you know that the air has to go into a filter, down pipework, maybe through an air cooler and into the inlet manifold before entering the engine and as such, losses will occur as the air has to battle these restrictions - therefore causing losses or making it less efficient than is ideal. See the fluid dynamics link below.

The turbo itself has it's own efficiency islands too - the "compressor map" as it were and being an air pump can also suffer efficiency losses if not specced correctly/not operating at it's most efficient. The turbine side of the turbo can also have profound differences on things like spool, but if you want to know more specifics, take a look at the links above and below.

Anyway, due to the above factors to consider in terms of "what hp of turbo?", it is why I always say "get a turbo of at least 500hp!" - do some basic math for R32 differences then - 3.2/2.8 x 500 = 571hp as a rough guide.

There is more to it, for example many owners report higher flowing turbo's with the same turbine ar ratio are very, very similar in feel - i.e. the GT30 v GT35R, seem to have very little in terms of spool difference if the ar ratio is the same - i.e. both 0.82 T3.. Lot's of variables in tuning though - it's always a balancing act for end results!

Which actual turbo's then!!!!!!!!!!! I hear you say?

Well, the proven ones are usually the Garrett and Borg-Warner units. You can get cheaper versions, like the B-W S or Garrett T versions but they are rarely chosen. Why? The turbine side of the B-W S can be large - see Holset info below - or the T series aren't as readily available here in the UK although the journal and ball bearing T series are great budget or relatively budget versions which are often enjoyed by those in other markets like the US. 

In the UK, possibly EU at least, the best, readily available options are the Garrett GT/GTX and Borg-Warner EFR turbo's - all very advanced and highly proven. You'll be looking at a minimum of £1k+ most likely though for these but they are usually considered the best.

So let's briefly look at the turbine ar rato of these turbo's:

0.63ar/equiv - good low end/spool due to high air velocity at low volumes but can ultimately choke up top - prob best for 4 cyl - ultimate air flow being the problem!

0.82/0.83 ar equiv - preferred choice for road use, a bar of boost at roughly 3500rpms, good flow bottom to top - can do 600hp too!

1+ ar - good for hp chasers, weekend toys etc, big top end but not always favoured for daily's due to poorer gas dynamics at low loads.

Air speed velocity can help at low loads, a smaller orifice will have x amount of air pass through it quicker than a larger one but too high mach numbers up top are less ideal as they can introduce turbulent flow - Google laminar flow. The preferred turbo's mentioned have both T3 ad T4 flanges so these air speeds/traits should be thought about. same single or twin scroll turbo. Almost every owner I have spoken to usually opts for a GT35R T3 0.82 and they have always been happy, but some prefer a little more lag, whether that's the driving style or drivetrain protection, so sometimes big ar ratio's and T4 flanges are chosen.

Outside of these variants then let's see;

Holset are also a favorite of owners with a few I know enjoying them! These are commercial, can be tons about but are usually used on big diesels, as such, check turbine side as they can be HUGE, good scrap yard finds though and cheap if you can get a supplier of them! I know compressor racing on ebay does them now and again and the turbine is specced/changed for petrol led build's with happy buyers - maybe worth a look? Being workhorses on high temp diesels they tend to be bulletproof.

There is also a number of other options - some decent JDM turbo's on the bay, thrust journal bearing mind you in terms of cost to think about comparatively, but well proven in such circles - just remember though that with import duties on any outside UK/EU you're looking at x 1.25 the cost of item plus postage to your door if not bought within UK/EU. Some nice billet items there and a bit cheaper so worth a look, but factor in these additional duties if you get quotes from domestic suppliers and their turbo's. It could be a case of them being nearly the same cost as a dual ball bearing turbo for example!

Precision Turbo's can also be found on the bay, mainly JDM usage here in the UK but many use in the States, not really au fait with them but lot's of big power builds read about  - more expensive for me to buy them than the major manufacturers above but supposedly well proven. Both journal and ball bearing options for broad cost variations and spec turbines as above.

Ebay cheapies - you'd be surprised what I can get these for in bulk! Different QC standards I would presume so do some homework - have a 20vt friend who was looking for a 300hp turbo - suggested a T series due to funds and around 12-14 months later he's just bought a BW billet KO4 as his 5th turbo and all others ebay spesh's that didn't hold up! 

Things like boost levels, heat levels etc all make a difference and his anti-lag most certainly didn't help! The thing I have learned from manufacturing techniques is that material specifications matter! Therefore, "you pay for what you get!" rings true. Very sensible boost/stresses - these cheapies seem to hold up quite well at times according to some owners, if not - well, read above! 

So, summary;

"You pay for what you get" - compressors spinning at hundreds of thousands of revs, 1000 degree exhaust temps etc - materials and manufacturing processes matter then! Oh - re: the stories about some manufacturers now working abroad and the turbo's now made "cheaply" - QC standards can be of an international standard and I would be surprised if a company that has spent heavily on R&D would suddenly tarnish their reps by using inferior materials/QC standards! Maybe cheaper labour outsourcing, but can't see where named/proven brands qualty would drop with that tbh.

GT35R most popular turbo chosen by owners for their daily's by far in my experience - 0.82AR T3 - 400-600hp well proven.

EFR also top spec - keep compressor/turbine similar to above, similar results

Various mid range turbo's, bit of shopping to do, some decent options mentioned - factor in taxes/duty compared with domestic suppliers, depends on your country/laws I suppose

Cheap generic - your risk, material, usage etc - can make big differences, you do pay for what you get in this area though! Some have worked, most haven't in my exp - I would say if you're struggling and on a budget, keep boost very low and not too many heat cycles until you can afford a more expensive one.

T3/T4 etc flange, turbines - basic guide as above.

*** Note: You may also want to factor in your tune, some can be very turbo & fuel specific, some pay more for custom work in this area but that 440cc tune may not be ideal for your GTX42! Just a thought! ;-) ***

 

Anyway, my 2p from my experience, hope it helps you choose and hope it helps the mods that pull their hair out for being asked this question time and time again!

 

Edited by RBPE
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Had a good question crop up;"What internally gated turbo?"

 

Garret do internally gated versions of their GT range, often with "wg" in their name, e.g. GT3076R-WG for wastegated. I think they go as far as 3582 models in size. 3076/3582WG should be similar. Holsets can be internal gate but on all turbo's without specified wastegate springs - make sure they aren't set up for high boost pressures.

The EFR range have internal gates too.

 

The JDM ones on the bay can be internally wastegated too - look for something bigger than 50lbs/min/500hp - likely with 74/75mm+ compressor exducer and 63-65mm+ turbine inducer sizes on at least a T3 flange as a guide.

Edited by RBPE
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  • 2 weeks later...
20 hours ago, JakeP said:

Ive looked on Turbo Dynamics, and is it me or do they no longer sell the GT3582r?

Doesn't seem to be on their website, I would recommend giving them a call. I recently had to replace my compressor wheel due to damage from an oring falling into the intake pipe. £25 for a GT3582R compressor wheel. They buy the GT35 in, then replace the wheels with custom or billet ones so they have plenty cast ones on the shelf which are cheap 

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On 5/17/2016 at 9:47 PM, JakeP said:

Emailed them and it seems they don't stock the gt3582r anymore , I'll have to get it somewhere else then

 

And it's by far the most popular one you lot ask for with me! Strange they've done that?

 I spoke to my sales rep and told him that some of you are looking for them but he's not got back to me yet, if there's a few of you asking maybe they'll get them back in?

 

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  • 2 months later...

Very helpful post and most interesting!! Thanks!! Would it be possible to expand into talking about transient response and characteristics, as well as power and reliability. I'm interested in finding out about good options for early spooling, quick responding turbos that would suit a 4mo bde engine. Not as concerned with ultimate numbers more real world performance and tractability with smooth consistent delivery throughout the Rev range. I'm reading as much as I can atmo. 

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On 8/21/2016 at 5:20 PM, G2t said:

Very helpful post and most interesting!! Thanks!! Would it be possible to expand into talking about transient response and characteristics, as well as power and reliability. I'm interested in finding out about good options for early spooling, quick responding turbos that would suit a 4mo bde engine. Not as concerned with ultimate numbers more real world performance and tractability with smooth consistent delivery throughout the Rev range. I'm reading as much as I can atmo. 

 

The Garrett guides are good for understanding a lot of the basics, a lot of things are in there. Can go into it more if need be, all are free to post up pertinent info!

 

One thing I will say is that I see a lot of people often led by marketing hype when it comes to choosing a turbo and especially with regards to those advertised as billet, seen it happen many times whilst they do not truly know what they are getting into.

 

The material specification of these compressor wheels is better than older ones simply due to the modern advancements of alloys, with numerous companies that I’ve looked at in recent years experimenting both in terms of alloy/material mixture content and manufacturing processes and of course, slight variances in materials used.

Most would have heard about, for example, forged aftermarket pistons, usually 2618 or 4032 alloy. Each variance in these alloys/manufacturing techniques changes the physical properties in various ways, in the piston example, if I remember rightly, although the 2618 alloy had properties that meant it could sustain higher temperature loads (thermal resistence) at the expense of expansion properties (i.e. the 2618 takes longer to expand as it can take more heat stress – hence the commonly used “rattly forged pistons” phrase being bandied about), the 4032 performed better at the usual thermal loads/temp’s sustained in an engine life cycle over the same period of time. Of course test data can vary and I think that particular company was actually marketing a hybrid, plus, in terms of pistons at least, there has also been developments in other manufacturing areas such as coatings, so that the most resilient material can be used and the physical downsides (in this instance the rattly sound before the material has sufficiently expanded), can therefore be reduced!

 

So for those who might get swept into marketing hype, the term “billet compressor” may mean a lot less than you think! It is the material specifications that make the real difference!

 

Most though will use 2618 alloy which means that compared with older material, less can be used, which in turn, relatively speaking, means less inertial mass (lighter so spins up faster) and why you hear “better spool” being bandied about!

 

Researching things like material spec’s and phrases like thermal resistence or stress or twisting/shearing forces should help you understand the changes made there.

 

Does this get you better flow then? Not necessarily! Although you could argue that less material used in a compressor would give slightly more space in the confines of the housing, it was the changes in the blade design when Garrett went GTX that increased the flow.

 

This is due to what’s known as (Computational) Fluid Dynamics, or to be more precise, gas dynamics. How flow works on a body. The re-design of the blade as this more modern material was being used, with the “re-profiled blade” or “extended tip technology” marketing lingo, is actually where the higher flow comes from. CFD testing can be done with computer modelling and modern development techniques coming on in leaps and bounds here as computers have advanced.

 

As many of you may get sucked into such marketing hype then, the word billet alone could mean very little, make sure the price differences reflect that. If it is new material has there been any blade profile changes for better flow? Does the price acurately reflect that too?

 

All things to think about when either choosing or upgrading a turbo.

Edited by RBPE
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  • 4 weeks later...

RE: GT35R

 

Garrett have changed the bearings and carriers on the GT35R now and offer them as supercores for the turbine section to be purchased separately (more expensive now :wacko:).

 

My suppliers are looking to see if there's any old units lying about in the warehouses if anyone's dead set on these at this present time?

 

EDIT - Garrett now changing their catalogue

Edited by RBPE
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  • 2 months later...

Hi All,

 

I am starting a fresh a3 3.2 DSG build shortly, looking for end number of around 550-600hp using an EFR 7670.

 

Does this seem correct turbo for my end goal or should I go a size up to protect the drive train?

 

I have a very good exhaust fabricator locally for turbo down but any advice on sourcing a cast manifold for an EFR?

 

Thanks,

 

Steve  

 

 

 

 

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It's pushing the limit's of the 7670 a bit that, 8374 might be better, more efficient. The 2 I'm dealing with at the moment are both running GT40's so they can handle big turbo's!

Cast mani, there's a few choices. People normally go for knock off SPA Turbo ones, I'm bias but I'd say an original one with T4 flange using the 0.92ar might be an idea. Failing that the HPA ones are probably the best, got the twin lambda bosses in too. CTS T4 ones look quite good too with their inconel. Few choices there.

Personally, if you have a fabricator, have them weld up a twinscroll manifold coming off the stock 3-1's and use the 8374 twin-scroll 1.05a/r for that top end if you're looking at the 600's mark! 

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Thanks RBPE,

 

Do you know where is best to get one of the HPA manifolds in the UK or is it an import jobbie?

 

I have emailed you for prices ;) on the EFR units, would I be correct in thinking the equivalent garretts to the EFR options mentioned earlier would be GTX 3582r or 4088r?

 

What turbo would you go for EFR or Garrett, are there advantages to either?

 

Steve

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Both great sets of turbo's, main reasoning for most is usually the sheer length of the EFR's and the tight confines of the transverse bays. 

 

Direct from HPA usually for the manifold although I sometimes come across the odd HGP or Mallon one in the German classifieds if you keep an eye out - saves hundreds just check for cracks on pics although they tend to be honest in their descriptions - not got one at the mo tho.

 

I've not had an email through, I'll check the spam filters but rule of thumb you'll pay less than they are on ebay and I'll get best price, can change from day to day though with it being European based stock and post Brexit!

 

 

Edited by RBPE
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Cheers Guys - Car is being used for fast road and track, a weekend toy only not daily driver but I would prefer it retains some of its OEM drivability as I use it as a second car to transport the kids lol.

 

My intention is for it to stay quicker than the next 10 years worth of hot hatches/saloons (RS3/4 & C63/A45 etc), that's why I am thinking 550-600 hp.

 

PBPE - I will send you another email then when I decide on turbo lol, What power are the gt40's running and are they laggy compared to the 35's?

 

Keiron - I will take a look at the GTX3584RS, I cannot decide between smaller or larger turbo, do I really need more than 550hp ish I keep asking myself? would drivability and fun be more with this size turbo I wonder? 

 

Regards to manifolds I will keep an eye on german ebay as advised, take it none of these are any good?:

http://www.ebay.co.uk/itm/361837607228?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

http://www.ebay.co.uk/itm/201547223890?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

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  • 2 weeks later...

The top link is a Rothe knock off and the bottom link is an SPA knock off - neither of those companies like that fact, in fact Mallon stopped making his for the well known turbo companies I think due to it. It's the quality variances to think about, the differences in the 25 years of SPA casting and/or Rothe material spec which add's value and thing's like porosity in manufacturing for example;

 

http://www.afsinc.org/content.cfm?ItemNumber=6933

 

Do you really want to skimp when such things are subjected to 1000*C temp's? I believe Kev ran an SPA knock off on his DIY Turbo guide so have a read of that too!

 

Some info to look into if you want to learn variances in this area;

 

https://en.wikipedia.org/wiki/Heat_transfer

 

https://en.wikipedia.org/wiki/Thermal_conductivity

 

https://wings.buffalo.edu/eng/mae/cmrl/Materials for thermal conduction.pdf

 

(You have conduction and resistance don't forget so it's all to do with understanding thermal resilience to avoid things like manifold cracks or conduction for intercoolers etc).

 

 

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So Are these the genuine SPA articles then, I 100% do not want to skimp on anything for the build:

 

http://www.ebay.co.uk/itm/401242806223?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

http://www.ebay.co.uk/itm/131906343668?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

Would the Gtx3584rs or EFR 8374 work ok with this t3?

 

Its between the above two turbo's for me -  I believe the garret is more compact so easier install/fit but then I also like the integrated recirc valve on the EFR.

 

Need to decide and get started on buying bits :)

Edited by j1sgo
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Yeah. T3 turbo will fit T3 manifold, get the measurements for cars and try and work them out, can clock turbo's, counter-tap manifold for fitments etc, tune might be an important factor regarding the manifold to think about too - but these'll go off topic for this sticky.

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