Twin Turbo Setup (Not compound)

This compound turbo thing has come up many times, and as far as I've read is not all that Viable for the TDI.

What about a twin turbo setup, say Twin VNT17's " 1 turbo for cyl 1 and 3, and the second for cyl 2 and 4 ( or 1,2 and 3,4).

They can sit side by side as space is available, and I'm sure that a twin intercooler setup (like of the 225hp tt) would be doable.

With each turbo having to supply half the air of a single turbo setup I would imagine that it could be more efficiant, and you can run higher boost levels (2 30psi for example) as flow would not be such an issue.


Any Ideas?

Twin 15's might work better; spooling...

It's harder to make a turbo for a small mass flow rate than it is to make one for a big mass flow rate, and the efficiency will trend towards being poorer for the same pressure ratio. (More paths for leakage; more surface area to create fluid friction against; etc.) The TDI turbo is already darn small, and making two of them that are designed for half the mass flow rate will generally be less efficient than what we have.

Also, if you want to do this, the cylinders to pair up are 1&4, and 2&3, since on an in-line four, those are the cylinders that are directly opposite in the firing order. The exhaust turbines will be getting flow through them which is even more unsteady than that of a single turbo fed from all four cylinders.

Not saying it can't be done, it just goes against what we know from accumulated experience.

I'm not so sure the engine even has enough exhaust energy to drive 2 turbos like that. The compound setup would harness unused exhaust energy passing out of the first turbine which isn't the case with parallel turbos. Parallel turbos might mean more flow IF they spooled but you still have to deal with compressor surge which the parallel turbos would make worse. To top it off, you're not going to get enough boost pressure to make this worthwhile. Parallel turbos are done more for packaging reasons than anything and you will almost always make more power with a single large turbo.

Compound turbos make the high pressure that they do because boost is multiplied rather than added. Lets say we have both running at a pressure ratio of 2. The first turbo receives atmospheric pressure of 1 bar and then puts out 1 bar of gauge pressure, or 2 bar absolute. The second turbo sees that 2 bar of pressure and doubles it yet again for a total of 4 bar absolute. That gives us 3 bar (~45 psi) of gauge pressure.

Fair enough,

I was just thinking of V6 with twin turbo's - the V engine and 2 cyl.

I never thought of it that way.

I like the idea - and agree that it's maybe not optimal in many ways. But just to throw another idea out there....

What about 2 VNT-15's in parallel, but sharing all 4 cylinders exhaust energy? One collector T's off to feed both turbos. The VNT mechanisim is adjusted to open later on one turbo than the other, that way they are "staged" in actuation. Bias the "closed" one really closed, but it can open up at higher flows and relieve the "normal" one.

On the compressor side, T off after the MAF sensor and feed both compressors. Not sure what to do on the compressor outlet side though? Just connect together I guess, not like it's going to flow backwards, but might put the slower spinning one in surge?

Lets take a turbo, reduce the amount of flow but ask for the same pressure ratio. What do we get? Compressor surge. This whole thing has bad idea written all over it.

Just man (or woman) up and put a real turbo on it

vwmikel,
Now I see your view, I was just thinking out loud ( and my brain doesen't always work that good.)

I'm still keeping my VNT17, and If I "have" to upgrade i'd probably go for a 2060, or whatever will be "best" on that date.

So guys we run on our GT25V special turbo 48psi of boost without surge? What other we need? Compound is acceptable if you run 70psi or even more boost but why for that low boost?

It's not hard to implement parallel-twins, but the layout is not favourable for a 4-cylinder engine because of the long dead-periods between exhaust pulses. To give you surge margin to operate the same pressure ratio with effectively half the mass-flow rate, you'd need 2 even smaller turbochargers than currently stock from the factory. The efficiency goes down the toilet (operating in inefficient part of the map; smaller turbos generally less efficient and more restrictive; doubling of rotating components and the attendent mechanical losses), which lead to the question, "What's the point, other than the novelty?"

Properly matched, a single turbo setup is good upto a pressure ratio of about 3 with pretty good efficiency. Staged turbocharging is implemented by the OEMs for no other reason than allowing a large turbo to operate in the high RPM operating range without the compromise of boost threshold and turbo lag in lower RPMs. Every current OEM implementation of a staged turbo setup actually has the small turbo deactivated or freewheeling while the big turbo alone does all the work at the top end. Only in a narrow part of the operating map are both turbos running simultaneously.

BMW and VW have a 2L twin-turbodiesels in the works; Opel had already prototyped a concept years ago, and PSA and Mercedes-Benz also have similar units. All are now making over 100 hp/L and will meet latest (European) emissions regulations.

It has nothing to do with efficiency it is a question of prestige.......long time ago has not to be a good diesel turbos with PR higher than 3 but now both garrett and borg warner make a new designed single turbos capable to handle PR ratio 5 without problems. Both design of vanes has been changed.....do you know that a second generations of Garrett GT30V, GT35V is a real?

you should make something like a VNT15 for the low rpms till 2500 and a GT20 or bigger for rpm's above 3000.. this would give ultimate driveability and top end, as found in a Mazda rx-7 with the sequential twin turbo setup.. and you can't even see the 2nd turbo kick in on the torque curve..

StingrayRT said:

It has nothing to do with efficiency it is a question of prestige.......long time ago has not to be a good diesel turbos with PR higher than 3 but now both garrett and borg warner make a new designed single turbos capable to handle PR ratio 5 without problems. Both design of vanes has been changed.....do you know that a second generations of Garrett GT30V, GT35V is a real?

Click to expand...

I am aware that new generations of turbochargers are increasing the maximum capable PRs. The latest 2.0L 140 PS TDI is actually using a smaller GT1646V turbo than previously less-powerful, smaller-displacement 1.9 TDIs, and the B-W KP39 is considerably smaller than the Garrett counterpart while installed in engines with similar power output. The 170 PS TDI is using the same frame-size GTB1749VM as the VNT-17 everyone is familiar with. 170 OEM horsepower would have been thought impossible with such a small turbo even recently. All these applications are operating at higher boost pressures than ever. The point here is not to disagree with you about the point of the increasing trend and capability of new generation turbos, but rather to confirm it.

But you seem to have access to information about turbochargers that are not out in the general market; the maps I have seen show compressors capable a PR of upto about 3.5, and these only in very large turbos. If you have maps showing otherwise, then please share.

Furthermore, as turbochargers get larger, these high PR numbers are generated only at high mass flow rates, beyond what most TDIs can take in, even when running at PR=3 at 4500 RPM, which is something I've been trying to explain for years. It has EVERYTHING to do with efficiency because efficiency is not just one fixed number for a given turbo, but varies with PR and mass flow. If you oversize the compressor, even if you clear the surge limit at the top-end, it will be less efficient (and therefore more charge heating and greater turbine work) than if the compressor were operating at its sweet spot (see red point in map below).



Like I said in another thread, the reason for staged-twin turbos, as far as the OEMs are concerned, is to eliminate the compromise between the desirability of a large turbo for top-end performance, and the boost threshold and turbo lag at the low-end. Every implementation of staged-turbocharging has the big turbo working alone at the top-end. If you don't care about the low-end, you don't need two turbos but just one big one.

tdi: just type "ETT Extened Tip Technology", garrett has always changed desing of compressor wheel and use a special black antifriction coating on compressor wheel....

Piranha said:

Fair enough,

I was just thinking of V6 with twin turbo's - the V engine and 2 cyl.

I never thought of it that way.

Click to expand...

V8's and V10's use dual VNT 17's to accomplish the task.

I was thinking of dual VNT12's on a 1.9..

StingrayRT said:

It has nothing to do with efficiency it is a question of prestige.......long time ago has not to be a good diesel turbos with PR higher than 3 but now both garrett and borg warner make a new designed single turbos capable to handle PR ratio 5 without problems. Both design of vanes has been changed.....do you know that a second generations of Garrett GT30V, GT35V is a real?

Click to expand...

The VNT30's and up are hydraulically controlled. I'd love to investigate the possibility of installing one in a TDI, however...

HMM, VNT30 would be interesting, but would it fit???
I know that ppl have managed to reduce lag significantly with VNT20's, maybe someone brave enough can try fit one.....
KERMAAAAAAAAAA, you seem to like experimenting!!!!


HMMMMMM 40psi boost and 300BHP would not be that difficult with such a turbo!!!

Piranha said:

HMM, VNT30 would be interesting, but would it fit???
I know that ppl have managed to reduce lag significantly with VNT20's, maybe someone brave enough can try fit one.....
KERMAAAAAAAAAA, you seem to like experimenting!!!!


HMMMMMM 40psi boost and 300BHP would not be that difficult with such a turbo!!!

Click to expand...

i know it could fit.. but the question is... how drivable would it be and how long would it last... thats a lot of cylinder preassure.. you would have to drop your ratio to even make that worth while trying..

Whenever you modify a car there is almost always a compromise of some sort. Turbos are no exception. A turbo that large will have a very high boost threshold so you probably wouldn't have decent boost pressure until about 3500 so you probably wouldn't have full boost until about 4000 RPM. That gives you about 1000 RPM to work with. Sure it'll make good power for that 1000 RPM but do you really want to give up power from 2000-3500? I've run a lot of numbers and it is my opinion that the VNT 20 nets you the best compromise of driveability and power. The VNT 22 leans more towards power as it compromises some low RPM power (more so than the 20) however the 20 cannot efficiently hold high boost at high RPM but the 22 can.

vwmikel how's your gt22 setup running? Any dyno tests, or track slips for us to drool over? Any problems with this setup? Any regrets going with this turbo over a vnt20? Just looking for more info .. for my next possible turbo upgrade!

I hope to dyno the car soon. I'm trying to get my hands on another set of injectors so I can get the race nozzles in first though. So far I don't think I can complain about the turbo. It makes plenty of power down low with tons of power from about 2500 on up to the limiter which I left at 5500. I usually don't rev it that high though as power peaks earlier than that.

I don't regret the 22 because I think the 20 would have been too peaky down low making it more difficult to drive. Most of the VNT 20's aren't really good for more than 26 psi from about 3000-3400 but have to drop back to 18 by 5000. The 2259 is good for about 27-28 from 3400-5000 making power come on a little later and keeping the curve flatter.

I see not any problem to spool turbo, you guys only change a turbos and that´s not enough for engine efficiency. I was made a full engine upgrade with huge GT25VNT start spooling from 1800rpm to redline - 3bar boost. We are damm fast a competitive gasoline engine need to have over 600hp! Next season a bigbore pistons, rods and other mods to break high 10sec.

Why doesn't it surge @ 1800 rpm and that boost?

My vnt20 surged at 1700rpm when going over 1.4bar boost when applying some throttle in the higer gears..

So we had to let it spool a bit later, now it only surges when in a gear higher than 2nd, give full throttle @ 1500 rpm or so and let of quick just before 2000 and then it makes such a nice sound this owns every diesel blow off valve I've heard

Rub87 said:

Why doesn't it surge @ 1800 rpm and that boost?

My vnt20 surged at 1700rpm when going over 1.4bar boost when applying some throttle in the higer gears..

So we had to let it spool a bit later, now it only surges when in a gear higher than 2nd, give full throttle @ 1500 rpm or so and let of quick just before 2000 and then it makes such a nice sound this owns every diesel blow off valve I've heard

Click to expand...

As you can see on picture we use a hybrid ported shroud GT25VNT and pulsed 4 - 2 - 1 turbo manifold both with 90mm turbo acceleration downpipe this can give us a pretty good low power.

So it doesn't surge because of the compressor housing..? I have 4-1 pipe manifold and 60mm accelerated downpipe..

StingrayRT said:

I see not any problem to spool turbo, you guys only change a turbos and that´s not enough for engine efficiency. I was made a full engine upgrade with huge GT25VNT start spooling from 1800rpm to redline - 3bar boost. We are damm fast a competitive gasoline engine need to have over 600hp! Next season a bigbore pistons, rods and other mods to break high 10sec.

Click to expand...

how would someone go about getting your style manifold to possably fit this to ... uh i dunno an 04 jetta PD????