606.962 Compound, Twin or Single VGT?

606.962 Compound, Twin or Single VGT? - Printable Version

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606.962 Compound, Twin or Single VGT? - CRD4x4 - 05-21-2013

Hypothetically speaking; if one had a OM606.962 and wanted to boosts power to the maximum HP that stock internals could safely handle, which turbo setup would YOU choose? (IP and injectors will be modified accordingly).

Turbos to choose from:
Garrett TV4502 "twin scroll" (a/r .60 compressor / 1.22 turbine)
Holset HE351VE (modified with 2-way vac/pressure actuator)
(2) Garrett GT2256V's (modified with 2-way vac/pressure actuators)

Would you...?

1. Twin 2256's (splitting duty 1-3 & 4-6)
2. Compound TV4502 (low pressure) and HE351V (high pressure)
3. Single HE351V
4. Other combo of above turbos

My initial "dream setup" would be the 351 feeding the 4502 but idk if there would be enough flow to properly spool the 4502.

Please advise.

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 05-21-2013

From just a little research I did, the tv4502 is only 64mm inducer.
351 would be a 60mm inducer. that would be too close to compound them.
What are the specs of the 2256v?

RE: 606.962 Compound, Twin or Single VGT? - Simpler=Better - 05-21-2013

The 2256v turbos are from a sprinter. I'm interested in this build as well Big Grin

I don't know if this applies or not:
[Image: gt22compress.jpg]

The one on the left:
[Image: 2256_vs_2260.JPG]

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 05-21-2013

Hmm. So that is 52 or 59mm inducer correct?
could do the 351 or tv4502 as LP, and the 52mm garret as HP.
Compound VNT would be awesomeness!

RE: 606.962 Compound, Twin or Single VGT? - CRD4x4 - 06-23-2013

I recently read a post that said that vnt turbos really "suck on a MB superengine" but I don't understand why.

This revelation could be the reason my post went generally unnoticed.

Could someone explain the theory behind why its bad or wrong to use a vnt/vgt on a high performance 606t?

Vnt/vgt compounding is my goal.

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 06-23-2013

I think if set up correctly it would be pretty awesome, allowing boost at a low rpm, which in turn should let you put more fuel to it earlier, and as being vnt it should also flow well at high rpm when the housings open a little.
That's just my thoughts Big Grin

I am also curious why they shy away from variable chargers

RE: 606.962 Compound, Twin or Single VGT? - aaa - 06-23-2013

They're more complicated and harder to find in the right size. Theoretically you should be able to get the best of both worlds, in practice the HE351VE does not deliver quite as much top end power as other holset turbos.

RE: 606.962 Compound, Twin or Single VGT? - Triker - 07-16-2013

Sorry my very bad english but I hope someone understand. I made om606 compound with Schwitzer S2B and S300 with two 60mm wastegates for C126 Merc. Smaller turbo starts spool under 2000rpm and the bigger comes together about 3000rpm and the acceleration is smooth at the end. Now I have just 120cc flathead 7mm and the pump´s feed rate ends but the bigger pump is coming. In a dyno the throttle linkage didn´t go at the end and there where about the ~20-30cc diesel to use so the power and torque left so low. Now the linkage is better and the throttle goes full.
My goal is to get more than 500hp this summer with early spool and smooth acceleration. Spool and acceleration are success for now and more power is coming.

But here you can see how soon compound with this setup spools.

[Image: IMG_20130709_172153_zps8ff3805c.jpg]

Here is the setup

[Image: 20130527_180157_zps671d8942.jpg]

[Image: IMG_20130606_150657_zpsfadbefa9.jpg]

Some adjusting and pull
http://youtu.be/yaAbKesv6K8

RE: 606.962 Compound, Twin or Single VGT? - Simpler=Better - 07-16-2013

It's gorgeous! You might have to do that buddy

RE: 606.962 Compound, Twin or Single VGT? - HaavardPYA - 07-16-2013

More pics of manifolds etc Big Grin

RE: 606.962 Compound, Twin or Single VGT? - Triker - 07-16-2013

(07-16-2013, 09:46 AM)HaavardPYA More pics of manifolds etc

Here is some pics

Now there is a scoop over the turbo and side pipe from the passenger side. But I have´t got no picture of those

[Image: IMG_20130606_102232_zps42375b89.jpg]

Exhaust manifold. Inner diameter of the manifold is 42mm

[Image: C360_2012-12-16-11-12-56_zps8a58327c.jpg]

Intake manifold

[Image: 20130523_171617_zpsdaaa28c3.jpg]

How the pipes goes. Downpipe is 3,5" with the screampipe from the second wastegate.

Some head work

[Image: 20130201_165551_zps7e81c3a0.jpg]

Transmission is modified by Finnish expert Siekkinen

RE: 606.962 Compound, Twin or Single VGT? - raysorenson - 07-16-2013

(06-23-2013, 09:33 PM)CRD4x4 I recently read a post that said that vnt turbos really "suck on a MB superengine" but I don't understand why.

This revelation could be the reason my post went generally unnoticed.

Could someone explain the theory behind why its bad or wrong to use a vnt/vgt on a high performance 606t?

Vnt/vgt compounding is my goal.

I noticed that Meken said they sucked on an MB, calling them an exhaust brake. Another poster said VNT installs were for folks that don't know anything about turbo tuning.

It's my assumption that there are a whole lot of folks installing VNT turbos with inadequate control of the hot side, giving VNT installs a bad name.

If you're planning to use a VNT in a max power scenario while using a pressure/vacuum wastegate actuator, you only have around 22"/HG of vacuum available to overcome spring force in the actuator. You would end up with too much boost in cruise and light throttle conditions. This would be fine if you were only boosting 1 bar.

RE: 606.962 Compound, Twin or Single VGT? - olefejer - 07-16-2013

Regarding VNT
I have had great success width both He351VE and HE341VE
First home-build manifold and HE351VE this one was giving 2.3 Boost width 2.0 bar EGP. at 5000 RPM
The HE341VE + KKD manifold, has a little more back pressure 2.2 boost and 2.2 bar EGP at 5000 RPM.
They can both handle all my Myna pump 7 mm can deliver.
The way i control it is width home-build controller, measuring both BOOST and EGP all the time and closing the wanes as much as possible, bot newer allow the EGP go higher then 0.3 bar higher then Boost,
That why it is not an EXHAUST BRAKE :-) but spool early.

http://www.youtube.com/watch?v=8dA9A_F9Ewk&feature=c4-overview&list=UUlCJDMTVUa85Os3bDbNaC2w

http://www.youtube.com/watch?v=ULEGavGRavs&feature=c4-overview&list=UUlCJDMTVUa85Os3bDbNaC2w

RE: 606.962 Compound, Twin or Single VGT? - Turbo - 07-16-2013

I am working on serie turbo set up where I have simulated
HP turbo efr 7163 LP turbo and GTX4508R, should be good for >800HP
but if BG is not going to release the 7163 soon I will go on different road
I do not dare to have some all originally components

VNT turbo can work but of Type DVANT so the VNT mecanism do not create to much pressure losses. garrett GTB3576VKLNR with GTX3576R compressor wheel would work for medium out put, or if used as HP unit it will be able to make some power

If somebody is just calling VNT exhaust brake is more telling of that persons limited knowledge in turbocharger technology, if you use old stuff there is no absolute not to make it work

There is big difference in in what generation of turbo is used only garrett have GT Gta GTb GTC GTD generations of turbo, and if you combine there racing turbos it can make dissent boost

and power is just not all about boost, the exhaust and intake system is playing a major part, If somebody is telling you they have a high out put motor with original intake I would say there is plenty more to come

If the exhaust pipe has to little volume vs to short the efficiency of the turbine at high boost is going to be low and big exhaust back pressure, in that case a more axial design of the turbine stage would be prefable

using booth intercooler and aftercooler would help further

then if you have really good amount of energy in the exhaust gases you can super cool the intake to -50 degree with turbo techology, but that is really more for an petrol engine

quote='raysorenson' pid='53620' dateline='1374001461']

(06-23-2013, 09:33 PM)CRD4x4 I recently read a post that said that vnt turbos really "suck on a MB superengine" but I don't understand why.

This revelation could be the reason my post went generally unnoticed.

Could someone explain the theory behind why its bad or wrong to use a vnt/vgt on a high performance 606t?

Vnt/vgt compounding is my goal.

RE: 606.962 Compound, Twin or Single VGT? - yankneck696 - 07-17-2013

THe he351VE can easily support 500 HP on a Cummins turbodiesel. Controlled correctly, it should do you fine. This is a well done install. Just a small issue on TC lockup
http://www.cumminsforum.com/forum/98-5-02-performance-parts-discussion/503779-my-he351ve-swap-pics.html

Ed

RE: 606.962 Compound, Twin or Single VGT? - offroaddieselhu - 07-17-2013

Hi,

I don't understand exactly what you want, but a well done VGT turbo control is a quite difficult task.To double this is a very great challange for everybody. I think to this you need very great experience. You should try after several hundredth. (although I do not know your experience)
I've seen various control on net tunning diesel forums and these sufficiently reveal the magnitude of the task. To make an actuator is such great task as to size a turbo. It's affect the work of the whole car.
(this "exaust brake" able to goes the car)
It's refer to Garett VGT, I don't know the Holset sytem (yet).

Offroaddieselhu

RE: 606.962 Compound, Twin or Single VGT? - Triker - 09-19-2013

Today one pump left to Dieselmeken to get 8mm plugs inside. Let see how C126 "compound STC" rocks after that Big Grin

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 09-20-2013

Besides being hard to fit under the hood, I think compound chargers are largely overlooked in the std field. What's not to like? Quick spool and great top end? If I ever had the money (and time) that's what I would be doing.
But as of now I have neither of those luxurys

RE: 606.962 Compound, Twin or Single VGT? - Triker - 09-20-2013

I've driven a number of STD configurations and the reason why I wanted to try a compound turbo setup was quick spool till the end. VNT / VGT charging might be certainly a good option for the right turbocharger, but the control is much more challenging than the two wastegate guidance if you want quick spool.
Someone says that the hx40super would have got the same results, but the added behavior is not what I want. Target power is now 550-600hp with early spool and I think the HP target is achievable with a new 8mm pump. Now with the small 7mm 120cc pump the combo has shown it´s nature and thats why I want to improve the setup.

RE: 606.962 Compound, Twin or Single VGT? - Triker - 10-11-2013

Dieselmeken 8mm with 220cc pump has arrived and installed. I have driven some adjusting and now it runs like HELL. Now it acts like CDI-engine reacts immediately to throttle pedal with no lag with a lot of power and it runs till the end very good. I couldn´t believe prechamber engine can react like that. Now there is 2.2bar intake manifold pressure and 1.0bar in bigger turbo.
Video is coming...

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 10-11-2013

(10-11-2013, 05:42 AM)Triker Dieselmeken 8mm with 220cc pump has arrived and installed. I have driven some adjusting and now it runs like HELL. Now it acts like CDI-engine reacts immediately to throttle pedal with no lag with a lot of power and it runs till the end very good. I couldn´t believe prechamber engine can react like that. Now there is 2.2bar intake manifold pressure and 1.0bar in bigger turbo.
Video is coming...

Awesome

RE: 606.962 Compound, Twin or Single VGT? - Triker - 10-12-2013

Some adjusting video 80-180km/h in third gear(722.3 and 2.24diff). Need to low back preboost feed because it now stucks primary turbo´s turbine housing. The IP is great and I have to be careful not to boom the engine.
http://youtu.be/uR-b-UJLwrU
Adjusting continues...
(sorry my bad english)

RE: 606.962 Compound, Twin or Single VGT? - CRD4x4 - 10-13-2013

Oh no!!
I want to watch this video so badly but YouTube says its "private" and won't let me watch it!
P.s your English is better than most Americans!

(10-12-2013, 03:17 PM)Triker Some adjusting video 80-180km/h in third gear(722.3 and 2.24diff). Need to low back preboost feed because it now stucks primary turbo´s turbine housing. The IP is great and I have to be careful not to boom the engine.
http://youtu.be/uR-b-UJLwrU
Adjusting continues...
(sorry my bad english)

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 10-13-2013

Same here on the YouTube video

RE: 606.962 Compound, Twin or Single VGT? - Triker - 10-14-2013

Oops sorry Blush

Now it should work.

I did some adjusting again today.
A couple of rounds preboost feed lower and a couple of rounds boost feed higher and one rounds both wastegates tighter.
Now the preboost feed won´t stuck primary turbo´s turbine housing at pedal to the metal acceleration.
Sweet Cool

Tried to film some video but it´s difficult to film with one hand and steer in other hand(I don´t have Gopro). I try to get someone to film also outside the car.

RE: 606.962 Compound, Twin or Single VGT? - Triker - 10-17-2013

Yeah Dodgy

Winter arrived to Finland and the Sec went to winter sleep. I reach to adjust it to work better with 2.2bar intake manifold pressure and 1.5 bar bigger turbo pressure and adjust the feed with and without the boost. It´s pretty difficult to adjust this setup with this 8mm pump but no impossible at all I can assure. So sad I couldn´t take it to dyno and adjust more because the damn snow. My goal was reach to 2.8-3.0bar intake manifold pressure and 2bar bigger turbo pressure with some minor smoke. Well now it´s time to make this setup better to next spring like Holley hp150 lift pump and better fuel filter bracket. It´s going to be Bosch fuel filter bracket with 14mm couplings and some more small modifications.
I update this thread perhaps next spring next time but if someone wants to know more about the setup or else I follow this STD site.

RE: 606.962 Compound, Twin or Single VGT? - Simpler=Better - 10-17-2013

No winter driving because of salt? I hate salted roads.

RE: 606.962 Compound, Twin or Single VGT? - Triker - 10-17-2013

(10-17-2013, 02:22 PM)Simpler=Better No winter driving because of salt? I hate salted roads.

Here they salt the roads in winter and that mean slippery roads and winter tyres and that´s not what I wait for the grip for adjusting. I have studded tyres in my carage for SEC but I have experience that they won´t last long Big Grin

and don´t give grip as much as tarmac. I´m sorry that I have only one poor adjusting video on this setup and I have moved it to private in "You tube" where setup worked a little bit poor because adjusting is quite exact. That film is not the best result what I have with this Sad

Burnout videos looks great but won´t give as much information about the setup as acceleration videos of speedometer and pressure gauges. I have reached some good adjustment about the spool, WG and fuel adjustment but not enough yet. I have to make some(like I said in previous message) modification to next spring to get maximum fuel capacity what I could get out of this setup like the pressures I said or more. I think there is plenty of capacity of this to get very good HP(over 550hp to 600hp without nitro) with early spool. Turbos working great and gives plenty of air. I was hoping that my friend could arrive to film some video for present adjustment but he didn´t reach before snow Sad

I know someone says that "If there is no film that´s not true" but some Finns know me and if have decided to do it and the world won´t collapse, I DO IT Wink

RE: 606.962 Compound, Twin or Single VGT? - Simpler=Better - 10-17-2013

The photos speak for themselves Smile

It's not like you're selling it and claiming 500hp with no proof Smile

I feel for you with the salt. Back home my Brother's truck is only a 98 but needs constant major attention due to the crumbling everything

RE: 606.962 Compound, Twin or Single VGT? - muuris - 10-18-2013

(07-17-2013, 06:16 AM)yankneck696 THe he351VE can easily support 500 HP on a Cummins turbodiesel. Controlled correctly, it should do you fine. This is a well done install. Just a small issue on TC lockup
http://www.cumminsforum.com/forum/98-5-02-performance-parts-discussion/503779-my-he351ve-swap-pics.html

Ed

I had OM606 with stock internals, 7mm 170cc IP and HE351VE, the best I got in dyno was just 402hp. I'd say it supports easily 350hp on these engines but for 400hp range it starts to make too much backpressure, and as a DI engine Cummins needs less air to make equal power. The spoolup wasn't that good either, not that big difference compared to HX40 super which is good for some 30-40hp more than 351.

RE: 606.962 Compound, Twin or Single VGT? - mantahead - 10-18-2013

is video still not working?

nice project, by the way.

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 10-18-2013

What did you do to control the he351ve?

RE: 606.962 Compound, Twin or Single VGT? - Triker - 10-19-2013

(10-18-2013, 03:36 PM)mantahead is video still not working?

nice project, by the way.

Not anymore. I let it be viewed a few days and everyone who wanted to see that small adjusting video has seen it Rolleyes

Like I said it was only a small clip of unfinished adjusting and testing and it didn´t give the best image about the setup yet.
There are plenty of people who disagree about the compound turbos and I want to show to them that they are wrong with video of high performance and early spool compound setup next spring when here is tarmac again Big Grin

RE: 606.962 Compound, Twin or Single VGT? - muuris - 10-19-2013

(10-18-2013, 09:49 PM)MFSuper90 What did you do to control the he351ve?

I got rid of the original actuator and used egp and boost to control it. Basically egp pushes vane ring to open-position naturally.

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 10-19-2013

(10-19-2013, 05:16 AM)muuris
(10-18-2013, 09:49 PM)MFSuper90 What did you do to control the he351ve?

I got rid of the original actuator and used egp and boost to control it. Basically egp pushes vane ring to open-position naturally.

There is a fellow on 4btswaps that made a electronic controller to control the 351 with the original actuator, pretty neat, I think it would help spool and top end power compared to EGP/boost.

RE: 606.962 Compound, Twin or Single VGT? - 95e300dez - 12-27-2013

I have a hx35 with a 12 cm housing and a k29 with a 20 cm housing both are split exhaust housing. I have been thinking of using them in a compound setup but only using half of the hx35 split housing. I would use a 50 or 60 mm wastegate to bleed of the exhaust to the second side of the k29. Just trying to get more power with less smoke.

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 12-28-2013

Those are Both pretty large chargers if your going to daily drive it, definitely wouldn't cut down on smoke because they wouldn't come into boost until late in the rpms.
What size is a k29? I know a k31 is 71mm inducer, never heard much about a k29

(10-19-2013, 07:43 AM)MFSuper90
(10-19-2013, 05:16 AM)muuris
(10-18-2013, 09:49 PM)MFSuper90 What did you do to control the he351ve?

I got rid of the original actuator and used egp and boost to control it. Basically egp pushes vane ring to open-position naturally.

There is a fellow on 4btswaps that made a electronic controller to control the 351 with the original actuator, pretty neat, I think it would help spool and top end power compared to EGP/boost.

RE: 606.962 Compound, Twin or Single VGT? - 95e300dez - 12-28-2013

The hx 35 boosts real good with a 12 cm housing I get 5 lbs at 2000 with using both sides of the exhaust housings. I figure I can double that if I only use one side of the 12cm housing.

The k29 flows 65lbs of air so it is good for 650 hp. Not sure on the size out of town will measure it when I gr back . The hx 35 is only good for 300 hp before it is being pushed to hard.

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 12-28-2013

The hx35 is 56mm inlet, and a what little research I did the k29 is ~47? But the turbine wheel is massive, and would probably outflow a hx35. So if those specs are right, a k29 is no bueno for twins

RE: 606.962 Compound, Twin or Single VGT? - 95e300dez - 12-28-2013

http://www.agpturbo.com/borg-warner-k29-3775-fmw/
I am not sure but this looks like my turbo but I think my exhaust is a t6 with a 20 cm exhaust. I will be home after the fuirst of the year and will get measurements to confirm.

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 12-29-2013

If those specs are correct from agp, it wouldn't be too bad. But it'll still be a smoke screen until that 35 lights. A hx35 for a low pressure and something like a hx30 or he221 for high would make a very nice spooling set of compounds in my opinion.

RE: 606.962 Compound, Twin or Single VGT? - muuris - 12-29-2013

(10-19-2013, 07:43 AM)MFSuper90
(10-19-2013, 05:16 AM)muuris
(10-18-2013, 09:49 PM)MFSuper90 What did you do to control the he351ve?

I got rid of the original actuator and used egp and boost to control it. Basically egp pushes vane ring to open-position naturally.

There is a fellow on 4btswaps that made a electronic controller to control the 351 with the original actuator, pretty neat, I think it would help spool and top end power compared to EGP/boost.

The turbo doesn't know how high tech the control mechanism is. I used an external spring to get the boost/egp ratio I wanted, a stopper screw to set vane ring closed-position and boost control ensured that vanes are fully open on full power. I tried several springs before I got the best result. Spoolup is bad if egp is much higher or lower than boost, it has to be in correlation and about 0,4bar higher on low end, about the same at midrange and even external wastegate couldn't help egp going too high at top end near 400hp. At 350 it worked ok. Original actuator couldn't have opened the vanes furher, so it wouldn't have helped.

RE: 606.962 Compound, Twin or Single VGT? - erling66 - 12-29-2013

To anyone who consider a VGT turbo for a high power setup:
Take a look inside the exhaust house and ask yourself, do I think all this exhaust flow restriction will help high end power?

RE: 606.962 Compound, Twin or Single VGT? - Turbo - 12-29-2013

I would be careful to make that kind of statement, I guess that BMW 550D engine is not a high end power for you then?

(12-29-2013, 03:18 AM)erling66 To anyone who consider a VGT turbo for a high power setup:
Take a look inside the exhaust house and ask yourself, do I think all this exhaust flow restriction will help high end power?

RE: 606.962 Compound, Twin or Single VGT? - CRD4x4 - 12-29-2013

The HE351VE that I'm planning to use on my 3.0L is from a 6.7L turbodiesel.
Its only logical that the "restriction" that you're referring to won't be an issue.
Others here probably use similar logic when researching and discussing their own projects.

Are there specific VGT set ups that you know should be avoided? If so, please share!

(12-29-2013, 03:18 AM)erling66 To anyone who consider a VGT turbo for a high power setup:
Take a look inside the exhaust house and ask yourself, do I think all this exhaust flow restriction will help high end power?

RE: 606.962 Compound, Twin or Single VGT? - Turbo - 12-29-2013

simply use a newer version of the VNT, VGT and it work better, but if you did not understand turbo machinery it can be very wrong and then it is called just bad turbo to much back pressure in my experience, but what do I know...

(12-29-2013, 10:31 AM)CRD4x4 The HE351VE that I'm planning to use on my 3.0L is from a 6.7L turbodiesel.
Its only logical that the "restriction" that you're referring to won't be an issue.
Others here probably use similar logic when researching and discussing their own projects.

Are there specific VGT set ups that you know should be avoided? If so, please share!

(12-29-2013, 03:18 AM)erling66 To anyone who consider a VGT turbo for a high power setup:
Take a look inside the exhaust house and ask yourself, do I think all this exhaust flow restriction will help high end power?

RE: 606.962 Compound, Twin or Single VGT? - erling66 - 12-29-2013

A statement is an opinion and not necessarily a fact, but I did not make any statement, just a question so people could think for themselves Smile

To quote Jeemu " no VGT goes on any of my cars" I wonder why if they are so great Rolleyes

The BMW 550D was an interesting read. Thanks for the tip "Turbo"

RE: 606.962 Compound, Twin or Single VGT? - MFSuper90 - 12-29-2013

(12-29-2013, 10:31 AM)CRD4x4 The HE351VE that I'm planning to use on my 3.0L is from a 6.7L turbodiesel.
Its only logical that the "restriction" that you're referring to won't be an issue.
Others here probably use similar logic when researching and discussing their own projects.

Are there specific VGT set ups that you know should be avoided? If so, please share!

A fellow on 4btswaps by the name of steed made a very nice programmer for the 351ve. He can program it to fit your needs, and you can manually control the vanes in the turbo with a potentiometer. Pretty cool if you ask me Smile

Edit: I forgot to mention he builds several of them and sells them to people

RE: 606.962 Compound, Twin or Single VGT? - Turbo - 12-29-2013

Jeemu possesses decisiveness to put things together, perhaps turbomachinery is not his strongest ability...
this is not as bad as well
http://turbo.honeywell.com/whats-new-in-turbo/story/honeywell-vnt-technology-helps-audi-make-history-at-le-mans/
the GTB2260VKLR can make somem nice things as well as the
GTB3576KLNRV turbo

RE: 606.962 Compound, Twin or Single VGT? - Mark_M - 12-29-2013

(12-29-2013, 06:13 AM)Turbo I would be careful to make that kind of statement, I guess that BMW 550D engine is not a high end power for you then?

Variable chargers obviously perform very well in both lower and high power engines. They are the basis for most modern diesel engines but to use a 550D as an example? It has three turbos and the large one isn't variable.
The TDV6 with their twin turbos still only have one of them being variable with the other high power turbo being normal fixed geometry. Its always the smaller turbo that is variable as well.
Like I said I think they are great turbos but I do also think there is a possibility for a restriction to be there. If there was an advantage to using a large variable turbo or all variable in a sequential system I am pretty sure manufacturers would do so.