Compound turbo discussion

Hi guys, i am looking at making a compound turbocharger with a vl35 from a 100Bhp fiat doblo 1.9 D engine and a gt2559v with a billet compressor 71mm in size, what do you think about my choice of turbos ? Will the HP turbo spool the LP turbo satisfactory ? The VL35 is wastegated and the gt2559v is VNT... The turbos will go onto a t4 transporter 2.5 tdi ACV engine, 102 Bhp ! Is it better to use a bv43a as HP turbo or the vl35 will be sufficient ? Thanks for any suggestions in advance !

adamss24 said:

Hi guys, i am looking at making a compound turbocharger with a vl35 from a 100Bhp fiat doblo 1.9 D engine and a gt2559v with a billet compressor 71mm in size, what do you think about my choice of turbos ? Will the HP turbo spool the LP turbo satisfactory ? The VL35 is wastegated and the gt2559v is VNT... The turbos will go onto a t4 transporter 2.5 tdi ACV engine, 102 Bhp ! Is it better to use a bv43a as HP turbo or the vl35 will be sufficient ? Thanks for any suggestions in advance !

Click to expand...

Show me both compressor maps and the turbine map for the small one and I might be able to tell you more. Generally using a VNT turbo for the LP turbo is not the optimal solution and from a DIY compound perspective using any VNT turbo will give you headaches... (EMP and tuning issues)

Yup! I know this by a painful experience!

Going vnt is not impossible to sort out I've done that on both of my car's and had great success.I decided to use 2 vnt's and both are controlled using one n75.I'm using the bv43 (pd) and a 2256v made from 3 other turbo's.The 56mm comp wheel has a 45mm inducer.

I'll see if I can manage to make a video showing emp,n75 vaccum,manifold boost and between stage boost.

If you run a fixed geometry high pressure turbo then don't use a vnt as the low pressure stage.The other way around is ok when sized correctly (very tricky).I went with with a vnt for the low pressure unit as I can fine tune it much easier than a fixed turbo (been there done that like JFettig also).

Basically I would stick with either 2 vnt turbo's or 2 fixed ones for ease of tuning.

I'm running 2 vnt's on my daily and have 2 fixed ones for the drag car.

Need to know more about the turbine and compressor size's that you plan on using before making suggestions.

I'm running one VNT with a "dumb" atmospheric huffer, and it is pretty easy to tune, so far. I'm not much into scratching the surface of getting all I can out of the setup yet, though.

Big VNT might get a bit odd, but with gauges on all pressure stages you can get a good idea on what's doing what and compensate with adjustments to programming, stops, or springs to suit.

ETA: anyone know where to find a compressor map for a K03-005? The only one I've found that is claimed to be shows it moving significantly less airmass than a GT1749V, despite its dimensions being larger in every respect. They're both relatively modern looking designs, has compressor efficiency really improved that much in the last however many years?

When using a vnt for the high pressure turbo and a fixed geometry turbo for the low pressure it requires a careful match to keep the vnt from overspeeding before the big one comes on.

Also if using a fixed geometry low pressure turbo without a wastegate it requires even more care.Having too big or too small of turbine housing/wheel can be too much of a pain to dial in using trial and error.

I'm not clever enough to engineer turbo setups like others.I have just learned from alot of real world trial and error and research.

Yeah. You can use pretty "small" vnt with quite large wg turbo as pair. For example ASZ/AHF with gtb1752v as HP and gt40 ad LP works just perfect.

diffas said:

Yeah. You can use pretty "small" vnt with quite large wg turbo as pair. For example ASZ/AHF with gtb1752v as HP and gt40 ad LP works just perfect.

Click to expand...

Dyno? More info?

Thesis about that car: http://www.theseus.fi/bitstream/handle/10024/86706/Laari_Markus.pdf?sequence=1
It`s in finnish but there are some photos and information about that car. Runs out of fuel with ultime 2...

andy2 said:

When using a vnt for the high pressure turbo and a fixed geometry turbo for the low pressure it requires a careful match to keep the vnt from overspeeding before the big one comes on.

Click to expand...

I have a wastegate to bypass HP (GTB1752v) turbine. It opens with ~1,8 bar boost (in intake manifold) so the HP can't overspin before LP (GT40) comes on.

Markus L said:

I have a wastegate to bypass HP (GTB1752v) turbine. It opens with ~1,8 bar boost (in intake manifold) so the HP can't overspin before LP (GT40) comes on.

Click to expand...

And no problems with the vnt regulation nozzling down once that wastegate opens to try to maintain the requested boost = EMP climbing sky high?

Alcaid said:

And no problems with the vnt regulation nozzling down once that wastegate opens to try to maintain the requested boost = EMP climbing sky high?

Click to expand...

I was surprised that there were no problems with EMP at all. Maybe that's because the boost request is quite low under 3000 rpm. No problems either when having full throttle after engine braking at high boost request range. LP builds boost quick in that rev range and also the N75 request is pretty high.

Generally EMP stays little under the boost through the whole rev range til 5500 rpm.

we managed to stop the vanes closing again once the LP started to spool well but response at higher RPM was poor.

With more testing i'm sure it could be made better!

Even with my vanes wide open EMP keeps climbing when IMP hits about 38psi. 70+psi EMP at over 45psi IMP.

vanes can open TOO much you know!

JFettig said:

Even with my vanes wide open EMP keeps climbing when IMP hits about 38psi. 70+psi EMP at over 45psi IMP.

Click to expand...

So you're not bypassing the turbine?

Mine's doing a similar thing, but with lower numbers.
Vanes are full open I'd assume (haven't fount N75 percent on the VCDS yet, but at the current boost request numbers it should be around 90% according to my maps) and EMP/IMP is 30ish/18ish

Just got a chinese 38mm wastegate to graft in around the high pressure turbine, see if it makes much difference. Gotta do some thinking on what all I want to reference it to, can put pressure on both sides of the diaphragm it looks like.

First I'm gonna try getting more pressure out of the atmospheric compressor, it's only doing 7 PSI right now, gonna put another spring on its WG and try for something around 12 PSI from that one.

diffas said:

Yeah. You can use pretty "small" vnt with quite large wg turbo as pair. For example ASZ/AHF with gtb1752v as HP and gt40 ad LP works just perfect.

Click to expand...

Garrett uses a gt32 paired with a gt40 when "staged/compound".

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

gtb1752v with gt40 is probably more in line with sequential system If I had to guess.

Rub87 said:

So you're not bypassing the turbine?

Click to expand...

I am,

andy2 said:

Garrett uses a gt32 paired with a gt40 when "staged/compound".

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

gtb1752v with gt40 is probably more in line with sequential system If I had to guess.

Click to expand...

I use those 2-staged with no compressor by-pass. Intercooling between compressors is needed. 56 mm trim 55 compressor would work in better efficiency area, but still this 52 mm trim 50 isn't choking. The main reason I'm using this HP turbo is because it was just laying around.

I don't know what turbine housing and trim Garrett uses in that GT32, but for example A/R 0.78 trim 73 flows ~20lbs/min. I think it's pretty close to GTB17V:s max (corrected) flow. Wastegate between turbines is 40 mm.

JFettig said:

Even with my vanes wide open EMP keeps climbing when IMP hits about 38psi. 70+psi EMP at over 45psi IMP.

Click to expand...

As far I have only 2.7 bar (39 PSI) max boost at 4000 rpm and 2.3 bar (33 PSI) at 5500 rpm and EMP is fine. In spring I'm going to rise boost a bit and see what happens. I think I can gain a little more power when AFR rises from 17.5 to 19.

Leaning the AFR is counterintuitive to increasing power...

JFettig said:

I am,

Click to expand...

So then your're saying the LP is really performing poor if the deltaP accros the HP tubine is almost zero? (bypassed)

Rub87 said:

So then your're saying the LP is really performing poor if the deltaP accros the HP tubine is almost zero? (bypassed)

Click to expand...

Don't think that Jon's LP wastegate is set that high so that HP turbine is fully bypassed, it is still requiring HP turbo to do some work to get up to the requested boost.

Ok, but normally if the wastegate is set to open at lets say 30 psi maniold pressure, and you're running 35 psi on the LP, the wg (bypass) should be fully open

Rub87 said:

Ok, but normally if the wastegate is set to open at lets say 30 psi maniold pressure, and you're running 35 psi on the LP, the wg (bypass) should be fully open

Click to expand...

No one with an overview of how to setup compounds would set LP that high and I know Jon knows how to set it up and share the load between the two stages.

High boost level on LP would be the case on a sequential setup, but then LP would be set even higher and there would also by a compressor bypass in there, not the case on his build.

ok, but with this numbers (imp/emp ratio) he is showing it makes no sense at all to keep it compound. Imo 38 psi is still on the low side to have benefit from multi stage compressor at high rpm. I have little idea of what pressure drop to expect over the HP compressor when the turbine is freewheeled. but if it would be only 1-3 psi it would still be beneficial to bypass the turbine completely and use the LP at PR 3,5-4:1

Rub87 said:

ok, but with this numbers (imp/emp ratio) he is showing it makes no sense at all to keep it compound. Imo 38 psi is still on the low side to have benefit from multi stage compressor at high rpm. I have little idea of what pressure drop to expect over the HP compressor when the turbine is freewheeled. but if it would be only 1-3 psi it would still be beneficial to bypass the turbine completely and use the LP at PR 3,5-4:1

Click to expand...

Near-instant response plays into the decision.
Also, I believe his has a relatively small port for the wastegate that bypasses the HP turbine. It is a mildly enlarged EGR port, so maybe 25mm in diameter or so. Couldn't go much bigger before running into the outside skin of the manifold.

I'm going to try boring mine out and brazing in a piece of pipe to get full flow of the 38mm wastegate I've got.

Ruben,

I have the LP pumping 20-22psi into the HP, the HP is bumping that up to 40-50psi depending on the tune. Yes, EMP is way high for some reason, typically above 3000rpm, it pegs the gauge but it holds IMP to spec. Part of my problem might be the EGR port I'm using for the bypass wastegate isn't much larger than stock(AFN manifold), it could be any number of things. The car is in storage for the winter, I'll mess with it again in the spring. I'm hoping to get it sorted out! I e-mailed you a while back about this hoping for some help but you must not have gotten the e-mail.

I need to tap into my LP EMP and even post LP turbo to see if there are any other restrictions causing this problem.

Ryan - when I ran only 15psi into the BV43 and kept boost around 45psi, the vanes didn't open fully but EMP still was very high.

crap must have read and not replied. too much emails too little time :/