VNT/VGT turbo appropriate for 3B?

[RufusTheDufus]

I've searched here but didn't find what I'm looking for. I'm thinking about tinkering with a microcontroller project to control a VW TDI-like VNT turbo suitable for 3B. (Vacuum operated VNT turbine type.)

Does such a turbo exist? My very quick searching turns up VNT turbos that are too small or too large for a 3.4l diesel.

Suggestions?

 

[gerg]

gt2256v was what I was going to do for fast spool and might add a wastegate to it for higher rpms. Its for a 2.8L sprinter van.

 

[slowandsteady BJ]

Oh Ill be watching this closely. Would be cool to have a VNT.

 

[RufusTheDufus]

There won't be much to watch for a while. I'm just planning parts at the moment.

 

[Dougal]

You could do a GT2256V, they'll handle ~140kw of airflow on a tdi engine, so likely ~120kw on a idi which means the 3B won't choke it.
The biggest problem with VNT's is choking out the turbine side.

I have a merc sprinter GT2256V which I bought with the intention of using on my 4BD1T. But now I've cracked the turbine sizing puzzle I've decided it'll be more of a brake than a help. For the 4BD1T at least wastegated turbos can do better, their turbines are more efficient and the wastegate keeps the turbine side under control.

The GT2052 wastegated turbos can do ~15psi by 2000rpm with a very safe tune. With a hotter tune they'd do even more. But you'll run out of fuel before you'll run out of turbo.

 

[RufusTheDufus]

The biggest problem with VNT's is choking out the turbine side.

Is the typical solution an exhaust pressure sensor fed into the logic that controls the actuator?


Any idea where I can get the specs for the GT2256V? I looked on the Garret website and didn't see that model.

 

[Dougal]

Is the typical solution an exhaust pressure sensor fed into the logic that controls the actuator?

Nah, you don't need to go that far. You'll have the vanes fully open by ~1500rpm anyway based on boost and choke won't happen till a lot further up the rpm range.

Any idea where I can get the specs for the GT2256V? I looked on the Garret website and didn't see that model.

There is nothing published for the GT2256V. I've spent a lot of time looking. There are also many different variants fitted to engines from ~120kw Merc Sprinter engines to the ~180kw BMW 3.0tdi. These variants have very different trims on the turbine wheels, I don't have reliable compressor specs except for the turbo I have which appears to match the wastegated Garrett GT2056 compressor for which maps are available.

The turbine side and choke I've essentially reverse engineered from the geometry. It's the best I can do and gets me in the ballpark.
The Sprinter turbo only puts out about 15psi max and 13psi at rated power.

 

[magnus_heydoc]

I'm in need of a lesson.
What does choking the turbo mean?

 

[Dougal]

I'm in need of a lesson.
What does choking the turbo mean?

Choking means the turbine can't pass more gas without either a decrease in temperature (EGT)or an increase in pressure.

Wastegated turbos run in choke and use the wastegate to increase/decrease drive pressure to regulate the power the turbine produces and thus regulate boost.

But on a VNT you've got no wastegate, so if your airflow requirements surpass the flow capacity for the turbine you're in for a lot of pain. The turbine starts to need a lot more pressure to pass more exhaust and this makes drive pressure spike and kills engine power but still delivers boost. Giving you the false impression that it because it's still making enough boost it should be working well.

It's a similar situation to clamping the wastegate on a turbo that needs the wastegate. You hit the wall power wise but still have plenty of boost. EGT can be okay but if you give it more fuel, it chokes even worse, hitting the wall at lower rpm.

On a 3B you'll probably be okay with a GT2256V. But for the 4BD1T I've run a couple of scenarios between a GT2256V and a GT2259 turbo with the same turbine but wastegated. The GT2259 was only a few psi behind at very low rpm and killed the V everywhere else. I've cut and pasted it here:

1. GT2256V VNT used on the merc ML270 (I have one of these turbos).
This turbo has a 0.64 A/R turbine housing and I've assumed the VNT can pull that down to about half the A/R.


2. GT2259 wastegated (used on Hino and Iveco diesels).
This turbo has a 0.56 A/R turbine housing and the compressor can flow about 10% more.

The results are interesting.
Low End.
Essentially the GT2259 turbo still spools just as quick. Both these turbos can provide enough boost to burn 140cc of fuel and produce over 600Nm of torque by 1400rpm.
And the wastegated turbo does with with less drive pressure.

Call it even.

Mid-range.
They are pretty much equal at 2000rpm, the wastegated turbo is running less drive pressure (because the turbine is more efficient without the extra vanes).
They can both provide more boost than needed through the mid-range, for the wastegated turbo that is no problem. You simply use the wastegate to cap boost and this lets the turbine breathe a bit easier.
But the VNT turbo still has to push that exhaust through the same turbine. The only way to get less power from the turbine is lower exhaust temp. The only way to do this is to run extra boost which costs power and spikes the exhaust drive pressure.

By 2,500rpm the VNT is running 5psi more drive pressure than the wastegated turbo.

Winner, the wastegated turbo.

Top End.
The VNT has a smaller compressor, it can only do about 27lb/min which starts to cap power at the 2,700rpm point. Now we've already had to drop off max fuel with this turbo as the turbine starts to spike and not be able to flow all the exhaust at max EGT.
So from here we're continually droppping fuel and boost to stay within the limits of the turbine and compressor.
In fact, we passed peak power (~150kw) at about 2,500rpm and have been losing ever since.
Drive pressures also keep spiking and are over 30psi by 3000rpm. Basically the party is over and it's time to change gear.

The wastegated turbo keeps producing more boost and power to beat the engines dropping VE. The larger compressor doesn't start to cap power until around 3,200rpm. At which point 140cc of diesel will be delivering around 180kw.
Drive pressures are comparable to the VNT, but the boost and power are well head.

Winner. Wastegated GT2259.

Summary GT2256V
Torque over 600Nm from 1400-2400rpm
Max power approx 150kw at 2,500rpm. 27psi here.
Limited by compressor and turbine flow limits.

Summary GT2259
Torque over 600Nm from 1400-2600rpm.
Max power approx 180kw at 3,200rpm. 26psi here.
Limited by compressor flow.

So this size VNT turbo has no real advantage on our engines unless you are already limited to lower power through other driveline concerns. We need bigger VNT's for these engines, a GT2359V might do it, but I have no info on those.

Clearly Hino, Iveco and the others running GT2259's on 4-5 litre diesels have already done this work. It's always good to agree with the big boys.

 

[RufusTheDufus]

I've actively started working on this project finally. (I built a house in the mean time.) Will be interesting and fun to test out a bunch of turbos and collect data on what works well and what works not-so-well.

 

[Dougal]

I've actively started working on this project finally. (I built a house in the mean time.) Will be interesting and fun to test out a bunch of turbos and collect data on what works well and what works not-so-well.

I've still got that GT2256V if you want to make me an offer!

 

[RufusTheDufus]

Dougal - Could you post a photo of it? It may be the same one I have already. I think I have 3 of the 2256Vs now. ( I forget at the moment.) I have one from an Iveco, one from the Merc/Sprinter and one from the BMW 3 liter.

 

[Dougal]

Dougal - Could you post a photo of it? It may be the same one I have already. I think I have 3 of the 2256Vs now. ( I forget at the moment.) I have one from an Iveco, one from the Merc/Sprinter and one from the BMW 3 liter.

This is the only pic I've got handy. It's one of the more common variations of GT2256V. Exhaust out is a marmon type flange, exhaust in is a mercedes triangle thing.

 

[Mcreight911]

@Dougal gtb2260vk ? I've used it to 220hp on a 3L common-rail . Might run out of turbine flow depending on power desired

 

[RufusTheDufus]

Might be a small fortune to post it to me in Maine. But I'm interested depending on price. I have a Chinese copy of one of those turbos and it would be nice to compare the real thing to the copy.

 

[cruisedeisel]

I love the technology behind the VNT turbos but...... WAY to many moving parts. Sounds like you have to service them often. Do you know how often they have to be cleaned of all the carbon build up? I will be watching but in theory.... The less moving parts, the more reliable.

 

[RufusTheDufus]

Yes, there are more moving parts in a VNT. But not that many more than some internal wastegate designs. I don't know they need to be cleaned more often. My only personal experience with a VNT was in my 2005 VW TDI. I bought it new. Never had to service the turbo and put 210k miles on it before selling it. I did do a few 'steam cleans' of the intake tract and turbo as recommended by some of the folks in the TDIClub forum. The "cleaning" process was to run it hard to get it hot and introduce a fine water spray into the intake near the turbo. I have no idea if it helped keep the turbo celan.

Most production vehicles have switched to VNTs. The new Ford EcoBoost engines use VNTs. OEMs have have different design guidelines and requirements for complex emission controls. A VNT makes some of these emissions processes possible. I doubt OEMs would be using them if they were inherently unreliable. Warranty repairs can really eat into profits.

I can say why I want a VNT: instantaneous boost, flatter torque curve, help in engine warm-up, possibility as an exhaust brake function, and there are more reasons I can't think of at the moment. I don't just want a VNT turbo, I want a complete system that works together to add fuel, monitor exhaust temps, engine load, exhaust back pressure, etc. I'd like a modern turbo system for my old diesel engine.

 

[gerg]

The VNT vanes are susceptible to carbon essentially freezing their motion. By revving the engine up in the rev range the vanes are forced to move open completely and will sweep the built up carbon out of the way. Good idea to do this as a routing habit rather than a scheduled maintenance item. By doing this daily when you drive it will prevent it from building up to a substantial level. I think IDI engines might be more predisposed to build up due to the simple fact that they produce more carbon.

I would really caution you with the fine water spray into your compressor wheel. Can do tremendous erosion damage. Some folks have sprayed Mr clean into the exhaust housing of the turbo which literally dissolves the carbon. Don't get it on your skin or on aluminum for very long. Very caustic. That is only when it is frozen and is having problems. Still better to rev it up routinely rather than let it get so bad as to need chemicals. If you do water spraying would be prudent to do it post compressor.

Cool to see you doing this man. Look forward to seeing your set up.

 

[GTSSportCoupe]

By revving the engine up in the rev range the vanes are forced to move open completely and will sweep the built up carbon out of the way. Good idea to do this as a routing habit rather than a scheduled maintenance item. By doing this daily when you drive it will prevent it from building up to a substantial level.

Sounds like my driving style is well suited to a VNT turbo.

To the original poster, I look forward to seeing what you end up doing. I love little R&D projects like this for old Toyota motors!

 

[Dougal]

@Dougal gtb2260vk ? I've used it to 220hp on a 3L common-rail . Might run out of turbine flow depending on power desired

I don't know the exact turbine or compressor wheel measurements for those. Garretts naming convention is somewhat "flexible" for their VNT turbos so you don't know what you've got until you pull the covers off and measure. It's the wheel measurements that determine flow, the generation of the VNT turbine detemines efficiency.

My 2.0tdi runs a GT1646V which is apparently B generation and I think it's not a long way off 200hp.

VNT's only clog up if the engine doesn't run hard enough, often enough. Keep the engine size realistic, get the EGT up occasionally and you're good.
If you drive 2km to work and shut it off still cold every day then you're going to have a bad time. Especially if you're doing that in a 6-7 litre diese pickup.