What could be causing my compressor surge?

T

tmorgan4

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Hi all,

I am running into a very interesting problem and looking for suggestions because I am stumped!

I sourced a new turbocharger for a 7.8L Duramax and I'm having terrible surge issues. If I plot the points (pressure ratio and mass flow) on my compressor map it is well within the surge line. I have used this same turbo (Borg Warner S200SX-50, 177267, 50mm inducer 70mm exducer) on other engines and this has never been a problem.

What else am I overlooking on the engine side that could contribute to surge? One thing I found after doing some research is 'wear of fuel injection valves'. Can anyone explain this? Please feel free to post any other ideas! :soap:
 
Your problem is you need to eliminate 5.0 liters of displacement and you're problem will be gone. Lol.
 
I can't really fault you guys for thinking this turbo is way too small because I had the same first impression before I ran the numbers. Besides, if the turbo was too small I'd be having an issue with choke not surge. Surge is typically a sign of a turbo that is too large. What am I missing??? :confused:

7.8L is a large engine but it runs at low enough speeds that I fail to see why this compressor is too small. I have seen 44 lb/min posted for the SX200-50 but I can't verify this number. If that's true then it out flows a HX35 by a small amount. These engines come in many different variations from 200-300hp. It has been very difficult to figure out what the factory turbo was. I have seen some links that show a Garrett GT3576d and some that say it's the GT3788VA that the 6.0 PSDs come with. Some in other countries appear to use IHI turbos. My guess is they used different turbos on different hp models.

Here is a data sheet I found for a 6HK1 (7.8L Duramax) for vehicle applications. On the high end of the values given this engine only puts out 680 lb-ft @ 1400rpm and 256 hp @ 2400rpm.

Keep in mind this is not a high-performance application like many guys on this forum. This is specifically an OEM replacement compressor which was sized to run an engine with EGR so a smaller compressor is required to keep the turbo out of surge at high EGR flow.

Going off Garretts rough sizing forumulas:

http://www.turbobygarrett.com/turbobygarrett/choosing_turbo

formula3.jpg


Using their provided values of BSFC=0.38 and AFR=22.0, my 44 lb/min turbo should be good for 316hp before it chokes.

So....are my calculations that far off? :Cheer:
 
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How would a turbine which is too small affect the surge? I fail to see how the turbine affects the surge whatsoever.

The only way I can see the turbine affecting surge is if the turbine is not capable of recovering enough energy to power the compressor in which case it could flutter in and out of boost.

The hot side of this turbo is a hybrid with a larger turbine so that is not the issue.
 
The problem most likely stems from the fact that compressor cover has no MWE groove.
 
Smokem said:
The problem most likely stems from the fact that compressor cover has no MWE groove.
Click to expand...

You may be right. It's right around this size where the manufacturers start putting the MWE groove in. I have seen publications on the MWE groove and it certainly helps move the surge line but didn't appear to be a drastic change.

Unfortunately Borg Warner does not make a housing with the MWE groove unless I go from the 50mm to 56mm compressor (inducer sizes).

I may need to look for a similarly sized compressor which already has a housing with the re-circulation channel built in.

Appreciate the replies. :Cheer:
 
It has been brought to my attention that some people seem to think I'm talking about a 50mm exducer (OD) compressor. 50mm is the inducer as that is the way Borg Warner specifies their sizes. It's a 70mm exducer.

Hope this clears up some of the confusion.
 
50 mm inducer and 70 mm exducer is still TINY for that size of engine. A stock dmax lly turbo is 63.5mm inducer and roughly 88mm exducer..that s250 you are trying to use is insanely to small for that engine.
 
mike diesel said:
50 mm inducer and 70 mm exducer is still TINY for that size of engine. A stock dmax lly turbo is 63.5mm inducer and roughly 88mm exducer..that s250 you are trying to use is insanely to small for that engine.
Click to expand...

Thanks for posting specs. I need to look up some basic specs on the LLY to compare them fully. My guess is they have a lower torque output but higher redline and peak horsepower.

After reading countless publications on the recirculation/MWE grooves I came across an idea which I hadn't considered previously. I have an enormous volume of charge air piping between the compressor outlet and intake manifold in addition to a huge Cummins air to water intercooler. It sounds like having too much volume downstream of the compressor can cause some interesting surge issues. Right now it's all 4.0" tubing which runs from the turbo (passenger side) across the top of the engine to the intercooler (driver side) and back to the intake manifold. I'll have to measure it to come up with an actual volume but I bet it's pretty substantial compared to what my compressor is flowing.
 
I would move to a 4" intake compressor such as 178034 at the minimum, depending on the power level you are looking for you could move to the 179078/179079 turbocharger depending on whether or not you would like an internal wastegate. This is very comparable in size to the GT3788 that is used on the light truck platforms. You very well could spend a great deal of time altering the upstream piping with little to no real World results as to surge reduction.
 
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Smokem said:
I would move to a 4" intake compressor such as 178034 at the minimum, depending on the power level you are looking for you could move to the 179078/179079 turbocharger depending on whether or not you would like an internal wastegate. This is very comparable in size to the GT3788 that is used on the light truck platforms. You very well could spend a great deal of time altering the upstream piping with little to no real World results as to surge reduction.
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Thanks for all the info. Seems like you know your stuff pretty well.

I'm happy to say that I figured it out...for the most part.

I ran some tests and it was in fact the huge volume of air that was forcing the surge line to move way further to the right than it shows on the map. Before this issue I have never run into a case where there is too much volume downstream. As it turns out, a tiny compressor coupled with 4.0" charge piping and enormous intercooler is not the best combination. Just for reference I measured the lengths of pipe and assuming a 50% intercooler density I have around 53 liters of volume of charged air including the intake plenum.

I believe that if I had a better compressor with a ported housing and a larger margin between my operating point and the surge line then I could get away with my current volume. I'm trying to run right on the line and it's going unstable.

I'm going to fabricate all new charge air plumbing with a smaller intercooler. According to Garrett's pipe sizing formula where they recommend staying in the 200-300 ft/s range it shows that 2.50" piping should be sufficient.
 
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