compound turbo idea

so I have been reading up on a few of the truck forums. Trucks that are equipped with VNT/VGT turbos are going compounds and in several conditions I have read about the VNT/VGT being the low pressure unit not the high pressure unit. This seems to me to be easier to deal with verse the reverse like has been used on several VW TDIs over the years. What would people think of using like a GTB2566 over a gt1548 or similar?

I'm just curious what the general TDI people would think about a set up like that.

This idea of using a vnt/vgt as the low pressure turbo and using possibly a fixed geometry high pressure turbo is news to me.

Would these vnt/vgt equipped trucks actually be ditching the vnt/vgt high pressure unit?

The 6.4L powerstroke is a great example of how a variable geometry high pressure turbo can be used with a fixed geometry non wastegated low pressure turbo.

Why would you want to go down a frame size? The GT17 turbine is already the restriction on an ALH.

If I were to do it again, I'd do two dumb WG turbos. TD04HL of your choice (saabs came with a real nice TD04HL-15T-5cm that'd light up plenty quick, dirt common in junkyards and on CL) or a holset (td04 based) HE2xx HP and an HX35 or better on the LP.

[486] said:

Why would you want to go down a frame size? The GT17 turbine is already the restriction on an ALH.

If I were to do it again, I'd do two dumb WG turbos. TD04HL of your choice (saabs came with a real nice TD04HL-15T-5cm that'd light up plenty quick, dirt common in junkyards and on CL) or a holset (td04 based) HE2xx HP and an HX35 or better on the LP.

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How exactly would a wastegated GT1548 be a restriction to the engine? The wastegate will be bypassing the turbine of the turbo not like the VNT in a GT17 which can not be bypassed. The GTB2566 is too big for most of the TDIs in anything close to stock so using it as a low pressure turbo will make it work fine as it won't take much from it to get more power then even the gtb2260 could do with no lag at all.

v8 coupe said:

How exactly would a wastegated GT1548 be a restriction to the engine? The wastegate will be bypassing the turbine of the turbo not like the VNT in a GT17 which can not be bypassed. The GTB2566 is too big for most of the TDIs in anything close to stock so using it as a low pressure turbo will make it work fine as it won't take much from it to get more power then even the gtb2260 could do with no lag at all.

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VNT can be bypassed... Problem with GT15 is it's poor turbine and compressor efficiency on higher flows even with stock head. GTB2566VK also has poor efficiency on high flows even as single. 2 turbos with bad overall efficiency is not the optimal basis for design.

v8 coupe said:

How exactly would a wastegated GT1548 be a restriction to the engine? The wastegate will be bypassing the turbine of the turbo not like the VNT in a GT17 which can not be bypassed.

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Damn, now that you said that the external gate fell off my VNT 1752s and ran under the deck. I'll have to make all kind of false promises to get it back out of there.

It isn't that it can't be bypassed, it is that it's just going to be extra dead weight when you're on the go pedal. Why even bother with sequential when the sky's the limit in regards to boost. On a gas motor you'll wreck stuff in a hurry with true compounds, with a diesel you just gain a little efficiency and move more air through the engine than you'd be burning. Good for a clean image of diesel performance.
GT15 is just too small for one of these motors.

I may have already wasted my time and typed too much.

I'm considering ditching my dual vnt compound's on my daily due to vane sticking issues.I was thinking about running a gt15 from the AHU and a fixed geometry low pressure turbo also.

The goal is still to keep things as clean burning as possible.With the 3.16 R&P and a drag clutch disc I need to spool quick and keep the smoke low.I don't mind giving up some HP for a cleanish running daily driver.

I'm guessing you're running MAP based smoke limiters?
I'm running a MAF from a VR6, with the linearization scaled by half to get around software limitations. It is real easy to get it to burn clean, even with it commanding the vanes wide open until 20 or so mg/str of fuel.

Yes,"speed density tune".I'm considering building a mechanical TDI pump using a late AAZ pump,etc.I Just put my VP pump back together tonight and found no issue.I'm really leaning towards TDI-M and fixed geometry turbo's.

Sorry to OP for derailing this thread.

Heh, every time I'm beating my head against the wall when my computer's unhappy for whatever german reason I'll look at the 4cyl MW pump I've got sitting next to a set of 4 13mm P pump elements and wonder if tuning the governor to idle properly would be less of a hassle than dealing with the demons of EDC15.

I would never ever go to a mechanical ve pump when you have ecu that can controll everything. For a Jeep conversion and for off road use mechanical is good option but for a street driven car its not. No control for timing and very limited control for afr.

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[486] said:

Heh, every time I'm beating my head against the wall when my computer's unhappy for whatever german reason I'll look at the 4cyl MW pump I've got sitting next to a set of 4 13mm P pump elements and wonder if tuning the governor to idle properly would be less of a hassle than dealing with the demons of EDC15.

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I would definitely try to stick with the mechanical VE pump for a daily before going inline without timing adavance however I do understand the point you ment to get across .

hatemi said:

I would never ever go to a mechanical ve pump when you have ecu that can controll everything. For a Jeep conversion and for off road use mechanical is good option but for a street driven car its not. No control for timing and very limited control for afr.

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If I were able to tune the ECU myself then I'd likey agree.The speed density tune AKA MAF delete basically converts my VP pump into a VE without an AFC imo.The problem is that I don't have the interest to learn how to make my own files or search the world for the ultimate tune $$$.I can burn a program into the chips but that is where I stopped.

Alot of tuning with the VP it seems is based on everything in the engine working 100% and being predictable.As compression gets lower over time then the tune would need to be adjusted to suit for example.

I'm attempting to tune the "dinosaur" VE pump to both start my ALH engine better and to run it cleaner than a custom tune with the VP.It's quite possible that I can prove myself wrong.My old AHU powered offroad buggy performs and starts well with the VE pump, similar compression and more fueling/turbo.

What about the factory compound?

I believe in Europe VW has a 235 HP TDI with a compound. It looks like a VNT for low pressure and fixed for high. It uses a waste gate to bypass the small turbo once the engine gets going. Could this set up not be duplicated on the earlier engines?

morpwr said:

I believe in Europe VW has a 235 HP TDI with a compound. It looks like a VNT for low pressure and fixed for high. It uses a waste gate to bypass the small turbo once the engine gets going. Could this set up not be duplicated on the earlier engines?

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For me it looks like VTG for HP and WG for LP

https://youtu.be/iL5lYWUSNPk

Thank you Markus

Thank you for the link Markus. Looks like it works great. Can't see any specs on turbo sizes, boost level. Maybe a GTD1449 going into a GTD2056 would approximate 230 BHP. If VW can offer this with warranty it seems 200 WBHP is available to anyone with some imagination. Just reverse engineer whats been done.

I am fine with this getting side barred with other discussions I like seeing it.

So if we are saying that a gt1549 and a GTB2566 aren't a great match fine I will admit I just grabbed those from stuff I knew existed and a better solution is probably out there. So lets come up with a solution for a 200-250WHP ALH and a 300-350WHP CR140.

If you guys are talking about the B8 Passat BITDI 240PS engine I believe it has a conventional VNT as the many turbo and an electric secondary to give the extra air needed to make that power. It also runs much higher rail pressure then the cr140s here in the US have ever run.

v8 coupe said:

and an electric secondary to give the extra air needed to make that power.

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Electric superchargers are not really something feasible to do with low voltage electrics. Maybe some day on a hybrid that already has high voltage juice. The power demands are just too high.

Ok so lets return to the true compound TDI idea with a built ALH so lets say the GTB2566 is not efficient enough what do we move to a GTB30xx? with what as a wastegated high pressure unit?

Wastegating the high pressure unit will simply take the turbine restriction out there and let that extra exhuast energy moved to the much bigger low pressure one.

Don't the Amarok TDI's have compound Turbo?

If using a vnt on a 2 stage/compound setup then definitely use it as the high pressure turbo IMO.No point in using a fixed geometry high pressure turbo and then low pressure vnt.

The idea behind using the high pressure vnt is that you get boost sooner and are able to control the turbine speed/flow by opening the vanes.Also If sized correctly you don't need a wastegate to bypass the HP turbine unless using Nitrous for example.

If you are set on using a fixed geometry high pressure turbo then use a fixed geometry low pressure turbo.

https://turbo.honeywell.com/twostage-turbo-in-series-configuration-gt32-gt40/

Its much easier to use two fixed geometry units.No need to deal with sticking vanes down the road

from what I have seen with the high pressure being the VNT on TDIs is it is an issue for tuning it because as the wastegate opens on the low pressure and the vnt opens it causes one of them to surge. I like the simplicity of having 2 wastegated turbos in compounds way simpler then one or two VNTS which can take hours on hours to get tuned. wastegates aren't in the ECU so you can tune the ECU and dial the wastegates in totally separate of each other. I am doing this on one of my TDIs after I get it on my Truck which is a VE engine so I should be able to get it to work fine.

v8 coupe said:

If you guys are talking about the B8 Passat BITDI 240PS engine I believe it has a conventional VNT as the many turbo and an electric secondary to give the extra air needed to make that power. It also runs much higher rail pressure then the cr140s here in the US have ever run.

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That's the CUAA. It does use two conventional turbochargers, no electric supercharger here. That's on the 268 HP 2.0 TDI.

Here's some nice data on the CUAA.

[486] said:

Electric superchargers are not really something feasible to do with low voltage electrics. Maybe some day on a hybrid that already has high voltage juice. The power demands are just too high.

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They are using them on the 268 HP 2.0 TDI and various TFSI motors. Don't know what all is in production yet. I thought I had before, but I can't find any detailed info on the 268 HP 2.0 TDI, so I don't know what voltage the electric supercharger runs at. That info might be gleaned from the TFSI data, but I'm too tired to search for anything at the moment, lol.

what I read was, is that Audi converted the whole car to 48V to be able
to run the electric turbo...

JW

Nope, 48VDC is for the electric turbo system only to reduce current.

ah ok, so they probably made the battery and alternator 48V
and transform to 12V for the rest...

JW

What about using a vent on the low pressure side and we unit for high pressure end which should have less to no lag plus no surge