Twin turbo V6 TDI

v8 coupe

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Could the 3.0TDI be converted from a medium size single to 2 smaller units?

To be more specific I believe stock they are like the GTB2260VK or BV50, correct me if im wrong. I was wondering if 2 GTD1752VRK could go on for more power and response.
 

TDIMeister

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There's nothing fundamentally preventing 2 small twins, but what problem is it you want to solve? More response? Do you have a 3.0 TDI now whose response you are finding to be lacking?
 

v8 coupe

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I was just thinking as an upgrade vs a single bigger upgrade unit. I see how VAG is solving it on the Bi-TDI with an electric basically small turbo. Giving a compounding aspect if I understand it correctly.
 

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Yes, that's right. Audi had it in an RS5 3.0 TDI ( https://forums.tdiclub.com/index.ph...all-bearing-turbochargers.517132/post-5680050 ) concept and in production in the and S7 and SQ7 V8 TDI

I thought you were thinking along the lines of conventional twin turbos, one for each bank of cylinders. The problem with this approach is that mounting two of the same kind of turbos will have fitment issues. Twin turbos for vee engine applications almost always have separate, mirrored left and right part numbers. The conventionally twin turboed V8, V10 and V12 TDIs have always been like this. Now, there no reason why these turbo pairs from one of these applications could not be adapted to the V6 but to be clear, they will be plumbed in parallel, not series (compounded). The best route to go is with the latest, highest output V8 TDI.

1632835604703.png

 
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TDIMeister

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The setup in the S7/SQ7 actually has three compressors - two conventional ones in addition to the electric one located near one of the charge coolers. The front and rear turbos are identified as a pair of GTD2056VZKLs apparently laid out in a parallel sequential manner:

SQ720164.0 BitDI4294.0/V8DGTD2056VZKL854379-0001057 145 653P

SQ720164.0 BitDI4294.0/V8DGTD2056VZKL854361-0001057 145 653N

There are even some for sale:

The plumbing and control of this is crazy complex, and Audi has gone to a "hot-vee" layout where the intake and exhaust ports are reversed in their positions from the usual in that that the exhaust blows into the space between the vee where the turbos sit and the intake is outboard of the vee.

1632835727611.jpeg

The only thing that might surpass this in complexity is the BMW quad-turbo Diesel inline-6 in the 50d.
 
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v8 coupe

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@TDIMeister I was thinking more traditional twins where it is a GTD1752VRK or similar per bank similar to how the 4.2TDI is.

I do understand that typically this is done with a Right and left bank designation. I'm also aware of the packaging space requirements. I'm thinking to have a more low rpm filled torque on a higher HP car.

Yes a drop in upgrade to stock single is easier, but if being swapped into a different chassis that's less relevant. The particular reason I'm considering twins vs singles is the car I'm contemplating swapping is already a gasser twin Turbo V6 so the boost side is semi-sorted. My thinking is once installed servicing anything in the engine bay is complicated. So I'm thinking do all major maintenance and upgrades first. Do a single round of major fab work, major tuning ironed out and running. I just am wondering if it would be possible on a stock setup. Can 2 VNTs be controlled by the ecu? Or the single vnt feed split? Or would it take a conversion to Vacuum based vnt control?
 

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A solution to an inexistent problem ! A 3.0 TDI can drive a large turbo without mici bother...
 

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A solution to an inexistent problem ! A 3.0 TDI can drive a large turbo without mici bother...
Yes I understand that, never said it couldn't.

What I'm asking is can it be done? I'm talking about going from a V6 TT gasser to a V6 TT TDI. I'm asking if it can technically work, regardless if anyone feels it's necessary.

I figure this would be the place to ask this question in my planning for a higher power performance based TDI conversion. Goal is ~350-450hp 3.0TDI into a C5 A6 Allroad 6-speed if you must know.
 

adamss24

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What I said In the above post should read this: why limit yourself to 250-300 Bhp airflow from 2x gtb1749xxx turbochargers when a single gtb2260vk can deliver the same flow at similar pressure without all the fabrication involved in such a modification! The v6 tdi inherent torque can make light work from driving such large turbochargers due to airflow trough the engine. Of course, if you want more low down torque you can use smaller turbochargers to move the torque plot lower down the rev range but it’s totally pointless as the gtb2260vk can make full boost at pretty much 2200-2500 rpms on its native engine ! All you will do it’s just get the torque converter to lock up quicker and put more strain on the gearbox and rest of the driveline. I have been as a passenger in Bobby Singh a4 3.0 tdi with massive turbo s300 and that car felt like a super car !
 

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A c5 allroad with a 3 plunger pump, gtb2260vk hybrid turbo and bosio race 683 nozzles will upset a Sachs sre clutch to the point that dmf and prop shaft will vibrate at anything under 1600 rpms ! I had such car running over 300-350 Bhp and trust me- there is no point going twin turbo !
 

diffas

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Yeah no point going twin - its so last season, instead go for three! :p

But to get serious, if you want to put twin just go for it. It is always nice to see different builds, sometimes they work and sometimes don't. Can't say my tri-turbo tdi is the easiest route to go but its fun. sometimes. :D I would go gtd1752vrk indeed and you get plenty of oomph. Sure you get bit laggier response and some low end torque is lost, but since they are installed closer to the exhaust valve you get bit better response than big single on the valley.
 

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A c5 allroad with a 3 plunger pump, gtb2260vk hybrid turbo and bosio race 683 nozzles will upset a Sachs sre clutch to the point that dmf and prop shaft will vibrate at anything under 1600 rpms ! I had such car running over 300-350 Bhp and trust me- there is no point going twin turbo !
Not talking old VE POS v6 I would be going CR 3.0TDI likely from a B7/8. I'm also not talking 300hp that's nearing the gtb2260vk limit. For twins there I'd certainly be looking at like a gtd14-15 not the gtb17s.

I'm talking higher HP like 400-500hp. You know where I'd be looking at something like DSDs GTD2872VRK or HE35. Stuff that isn't ideal on a small 3.0L engine. I'm talking like 200+ per bank, like the ALH norm. GTD1752VRK seems to be working pretty well for the 1.6TDI crowd. I do understand the differences between the two in this comparison. I actually think a pair of GTD1752VRKs on a 3.0TDI would be a great although not cheap upgrade.

I am really looking for if the currently available systems could control 2?

I am fully aware of the reasoning, logistics, packaging, etc of a twin turbo system. I'm not really asking if it should be done, but can it be with currently available tech?

@diffas I really am curious how the GTD1752VRK would be as twins on a 3.0TDI. From most of the 1.6TDI dynos I've seen they have like 120-150ft-lbs of torque at 1800rpm. The 1.6TDI also naturally isn't a torque king being a square engine with an 80.4mm stroke. That should shift the torque down a little from where it is on the 1.6TDI, but the fire rate and slight decrease in displacement will reduce spool a little.

Dark Side Developments (DSD) has gotten a 1.6TDI with a GTD1752VRK and 50% OS injectors to do 232HP/340ft-lbs. It peaks at like 2900-3300. So if a destroked 1.9L 16v I4 can do that I'd hope one on a 1.5L 12v I3 could do like 200/350.


Again to clarify I am not looking to replace single for twins at 250-350hp. I am asking for 400+hp where sizes start getting big fast.
 

diffas

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To be honest you can't have stock type of torque down low when you aiming such a power level, at least on single stage turbo system.
I would forget those silly hybrid turbos that are really restricted on power range and move up on size. There are loads of good results with s356v and s360v on 1.9 and 3.0tdi. Not so long time ago had dyno with 3.0tdi with s360v and it had max boost around 3000rpm and provider solid ~450hp/850nm with under 3bar of boost and with good EMP. Nowdays getting the air(turbo) is not the problem, but to get enough and quality fueling is a different story.
 

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Not trying to piss on your bonfire but allroad c5 and 450 Bhp just don’t mix together…the air suspension cannot cope with the power and it’s too heavy of a barge to handle properly ! Getting conventional shock and spring suspension will make it similar to a c5 a6 which is another can of worms to open ! I would choose carefully your ride especially as there is not enough room for big twins under the engine manifolds of the 3.0 tdi considering the c6 chassis is a little bit more accommodating compared to a c5. Prove me wrong and build the darn thing however internet it’s full of thousand Bhp projects that never materialized !
As diffas pointed above, single modern turbo can supply enough air to turn the earth around, it’s getting fueling and mapping right that is the main issue !
As per the piece of **** that the c5 2.5 tdi is, the later incarnations with cam roller heads are exactly like on the 3.0 tdi, they rev better and produce torque in the same manner…a 350 Bhp is a 350 Bhp engine regardless if CR or VE ! I do really wish you good luck with the build and whatever you do please keep us posted with the updates ! I too do like to go against the grain sometimes but I tend to choose the easy path on my power goals lately !
 

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One thing not to forget is that if you go twin gtd15 or 17, you still have to use rather high boost on 3.0 for 450-500hp. This means that compressors will not be in very efficient point. I would go staged or similar route what factory did with 3.0bitdi, maybe just larger LP turbo.
 

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Not talking old VE POS v6 I would be going CR 3.0TDI likely from a B7/8. I'm also not talking 300hp that's nearing the gtb2260vk limit. For twins there I'd certainly be looking at like a gtd14-15 not the gtb17s.

I'm talking higher HP like 400-500hp. You know where I'd be looking at something like DSDs GTD2872VRK or HE35. Stuff that isn't ideal on a small 3.0L engine. I'm talking like 200+ per bank, like the ALH norm. GTD1752VRK seems to be working pretty well for the 1.6TDI crowd. I do understand the differences between the two in this comparison. I actually think a pair of GTD1752VRKs on a 3.0TDI would be a great although not cheap upgrade.
You're certainly not going to get 500 on twin GT14-15s, and even 400 would be pushing it (cf. the discussion here), unless you have another big turbo that blows into the pair in a compounded setup (probably what diffas' tri-turbo setup is describing without having seen it).

Bottom line: There is no reason a pair of GTD1752VRKs on a 3.0TDI will fundamentally NOT work if you find a solution to left- and right-bank installation... If you're so inclined - go for it - I even have two GTD1752VRKs. Control is easy because you're just using the same N75 signal to drive both turbos - use the PWM directly to control the electronic actuators.
 

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Thanks for that - definitely done right and awesome fabrication work! Are the HPs a pair of KO4s? Given the side-flowing flange of the stock exhaust manifold, it would be ideal to mate that to a side-inlet turbine so that you don't have the long loop joining them together, but there are very few such options available. However, a pair of GTB2056VKLRs that have the side inlet would be great and support 500+HP with some sacrifice at the low-end without needing a third turbo.

For the OP, straightforward twins of the appropriate size for the target power (GTD1752VRK) would be the most straightforward to implement if you reject a large single. Diffas didn't say much about the boost control logic development and driveability, but the programming will be extremely complex and won't be something you simply flash once and go, but will involve a great deal of dialing-in to get right.
 

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Alternatively - and I haven't verified it to be sure that it fits, you could ostensibly take both the left- and right bank manifold and turbo sets from the V8 TDI, get rid of one primary from each, close up the resulting hole, and then fit them to the V6. Both engines have the same 90mm bore spacing... the unused 4th exhaust primary runner in each bank could also be used to place a HP turbine bypass.

The latest V8 TDI puts out 367 HP out of the factory, and the GTB1749VK turbos (813100/813101-004) are likely good for at least 400.
 
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TDIMeister

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@diffas, in your tri-turbo build, have you considered the feasibility of orienting the S356 90 degrees from the way shown in your pic?

49135326_2310007959033295_546974706599723008_n.jpg

That way, the turbine outlet flows straight to the back of the car and the compressor inlet to the front through the vee (don't know if there's room between the intake manifold for a boost pipe to go in between (earlier V8s even put an intercooler heat exchanger between the vee; would be good for an interstage cooler).
 

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One thing not to forget is that if you go twin gtd15 or 17, you still have to use rather high boost on 3.0 for 450-500hp. This means that compressors will not be in very efficient point. I would go staged or similar route what factory did with 3.0bitdi, maybe just larger LP turbo.
However, a pair of GTB2056VKLRs that have the side inlet would be great and support 500+HP with some sacrifice at the low-end without needing a third turbo.
@altz1, you're absolutely correct, it's not only about supported mass flow but required PR to reach a certain HP. I neglected this in my above statement and have to revise - man, that's what doing my Master thesis on turbocharging 12 years ago and not refreshing regularly will do - I forget!

Simple twins will not yield a high target HP/L without sufficiently high PR, even if the mass flow is sufficient. This thread should be a reference; the method and math will be the same but scaled for displacement: https://forums.tdiclub.com/index.php?threads/staged-turbo-sizing-math.208045/
 

diffas

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@diffas, in your tri-turbo build, have you considered the feasibility of orienting the S356 90 degrees from the way shown in your pic?

That way, the turbine outlet flows straight to the back of the car and the compressor inlet to the front through the vee (don't know if there's room between the intake manifold for a boost pipe to go in between (earlier V8s even put an intercooler heat exchanger between the vee; would be good for an interstage cooler).
Well In my opinion there is no space left for the turbo to be in any other direction. B5 engine bay is quite compact in size. That turbo is actually S362SXE with 0.91ar housing and HP ones are K03-029 from 1.8t (BFB). My original vision was HPs with little smaller compressor side to have better spoolup and transient response. I had 32-33mm compressor side on my mind, but went with stock 029 (36mm) since they looked quite nice on the turbine side and wg looked like it should flow pretty good. My boost control logic is quite simple, overall boost controls the HP turbo wastegates and LP has no WG at all since there is no need to waste any exhaust gas there. I wanted as simple setup as possible. So on the test runs I've ran I noticed that it looks like the LP turbine housing is too small, it makes almost 2.8bar boost out of 3.3bar. HP turbos have maximum pr on spooling 1.7 and on max boost something like 1.15. So it is almost like 2-stage instead compound...haha.
Like you pointed out it is possible to add extra wg:t to the manifold but didnt want use external ones yet, since it gets quite complicated and needs extra space. At some point it might be that I need to make the change but at that time I probably should go HP:s without the internal wg.

What comes to driveability it is not meant for daily driven anyway so lots of low end is lost there. Probably slightly decreased CR and regrinded cams kill bit low end and N/A power. And I don't use that rich mixture to spool up.

Here is the video from the gauges to see how it spools and pulls with break in ecu software:
Gauges are from the left: overall boost, left bank emp, right bank emp, LP boost and lambda gauge

Here is the dyno result from the past weekend:
 

diffas

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Nice build but it makes me think that single stage probably will not deliver pressure it is needed for 600-650hp that that setup
 

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I have very little faith in this 3.0 twin 2260vk project. It will be really sluggish in lower rpms with only 1,5L powering the 2260. For 600hp in 3.0 they need probably around 3+ bar boost and thats too much for gtb2260.

I built 4.2tdi with twin gtb2260vk myself and with normal boost/backpressure ratio full boost happens only after 3000rpm. 3000-4500 is very nice tough, close to 600hp right now, but with 2 extra cyilinders...
 

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Agreed. That's a lot of turbo to have effectively 1.5L of engine displacement to blow into on each bank. You need the boost pressure for the HP/L and doing it in a single stage is not optimal.

And, as diffas has found out, it's very tricky to size both sets of turbos to get the desired split of the boosting work done by each stage. As it is shown in diffas' video, the two small turbos are doing very little of the heavy lifting. You'd want to go with a larger A/R on the S362 and smaller on the KO3s (gasser 1.8t ones will be too high to begin with). Why didn't you stick to VNTs on the HP? I know you wanted simplicity, but then you must have converted from VNT in the original to driving a pair of WGs... Two small VNTs blowing into a large LP will definitely work and work well; it has been done by BMW, Mercedes-Benz, DAF and others. If you have a pathological hatred for VNTs, two KO3s from a Diesel application (1Z/AHU) will also work.
 

diffas

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Well on my case there is no work done by n75. HP wg are controlled by the overall boost and currently it is working quite nice as it is. At some point I will add mac-valve for better control over the boost. I'll probably go try out 1.0 a/r housing on s362sxe for next year since it is almost winter here so not gonna drive it anyway. Yea I know it is a quattro and should be driven through the winter. :D What comes to HP turbos I have not talked to turbo company yet if it is to install smaller compressor like mentioned before. Sure it means new housings that need to be modified to take boost lines on the intake side. This setups spools up as it is better than my earlier single wg turbo and it was the main goal. It was K26 with 51mm compressor paired with 58mm turbine and #5 turbine housing. It started to have too much backpressure for my taste when going higher boost levels above 2.3bar. I did run it max 2.5bar and it made 380hp with somewhat decent lambda between 1.05-1.15 on max power. My target is to have lambda 1.25 ->, so now it is quite good.
 
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