Can someone please explain "turbo surge" to me?

[dpuckett]

I have seen this term many times here and on other forums, and I know the technical reason/ cause/ operation for it, but I still am not sure I can identify it in the real world. Can someone please tell me what it is? I dont think I have ever heard it in person.



Daniel

 

[RustyJC]

In 50 words or less, it's airflow reversal through the turbocharger's compressor section because (1. ) the turbo speed dropped abruptly when someone lifts off the throttle or (2. ) the swallowing capacity of the engine dropped after an upshift. Please note - the turbocharger rotor does NOT stop or reverse rotation during surge. There's far too much rotational inertia for that. The unloading and loading of the compressor impeller can ultimately lead to shaft breakage due to cyclic fatigue failure, however.



It manifests itself as one or more "barks" or "chuffs" in rapid succession.



Rusty

 

[JLEONARD]

Here are 50 words and more about surge and turbos in general that I found on a quick search.



http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html





edit:

It manifests itself as one or more "barks" or "chuffs" in rapid succession

I believe that is what we have been calling "flutter".

 

[Forrest Nearing]

classic "surge" occurs when the compressor is trying to feed the engine more CFM than it can injest... not boost, but CFM... air flow... the engine simply can't flow that much air, and it's akin to putting your hand over the end of a vacuum cleaner hose... pressure drops, the compressor speeds up rapidly, then boost goes up, compressor slows down rapidly, pressure drops, compressor speeds up rapidly, etc. etc. etc. it makes a nasty noise and the boost needle bounces, and it's HARD on the turbine shaft and bearings.

 

[KMUNCASTER]

i hear ya...(it)

I just installed a high flow air cleaner on my 93, and it makes a neat snort or bark when you chop the throttle... . is it hard on it to allow it to do that ?



I guess I'll avoid it if so..... too bad... I kinda like it, but I also kinda like my truck to run reliably..... maybe it was always there, just couldn't hear it with the old airbox in place.



what to think ?



Diesel Dad

 

[CSchafer]

take air cleaner off, fun fith gear at full boost and have someone pull out in front of you. You'll find out if it surges. I could never hear it untill I got an open filter but it actually does it quite a bit.

 

[MMiller]

Mine will actually do it, while pulling my loaded trailer, in OD, running up a big hill. When engine rpm's start to come down, and the charger makes more air flow then the engine can take. The boost gauge starts to bounce, and then I have to carefully ease off the throttle, or it really barks the turbo. I suppose one of these days, I need to upgrade, and get a turbo that will help my airflow problems.



Michael

 

[CSchafer]

I upgraded and it barks worse. Now it really moves more air than the engine wants.

 

[dpuckett]

Ok, thanks, guys. It seems to me that porting the head would help with surge/bark more than anything? How can one get the right turbo/ fuel flow ratio to minimize surge? Or is it just trial and error?



DP

 

[Forrest Nearing]

porting the head will help... as will the right camshaft

 

[MMiller]

Swankmetal, or someone else posted a picture of a compressor housing with a groove machined inside it, and it helped with turbo surging. I am terrible at searching, maybe you can find it.



Michael

 

[Forrest Nearing]

I forgot I was on the 1st gen forum!



first upgrade should AT LEAST be an hx35 or hy35 off of a 2nd gen... you should be able to pick one up for a couple hundred bucks... far better upgrade than a 16cm housing on the stock turbo!

 

[RustyJC]

Swankmetal, or someone else posted a picture of a compressor housing with a groove machined inside it, and it helped with turbo surging. I am terrible at searching, maybe you can find it.



Michael

Yes, that would - at the cost of compressor efficiency. Large centrifugal compressors use surge control valves that recycle flow from the discharge back to the inlet when the surge control system senses the onset of surge or that the compressor is approaching the surge line. The groove would recycle air from the discharge back to the inlet all the time, which reduces ultimate performance and increases compressor discharge temperature. It's a tradeoff that may or may not be worth making.



Rusty

 

[Forrest Nearing]

don't forget it makes the turbo scream 10 times louder... well worth a little inefficiency at peak IMHO



I'll take a broader, more usable powerband over peak numbers any day.

 

[JLEONARD]

What? :-laf :-laf

I'll take a broader, more usable powerband over peak numbers any day

Me too.

 

[MMiller]

OK, this is much better then the last discussion we had on this topic... ... ... ... . If I were to put a HX or HY35 off a second gen, I suspect my pryo will go through the roof, due to lack of exhaust flow(I'm still running stock big exhaust housine) and my upper RPM power will be gone due to wastegate opening. My first gen keeps pulling like crazy, were as my dad's 95, and brother' 94 lay down as rpms increase.



All in all I like the way my stocker works for my application. The only two things I like to change are to lower the pryo reading, and stop the surging. I want to run fully loaded, pull OD, and let the cruise work, without having the turbo surging, and pryo exceeding 1300+*.



Michael

 

[Greenleaf]

In short, a local member has a "low flow" 60mm comp that surges from HTT. They told me it will. Apparently the hi'flow will not surge so that is what I have. The wheels are the same dia. ie 60mm but the wheels are totally different. Also John is useing the 14 non gated housing with his HTT 60 to tow loads through WV. May have something to do with the surge.

 

[MMiller]

So, Scott, can I borrow your turbo for a while to see if it will surge?? :-laf How will I know for sure if a turbo upgrade will solve my problem and not make it worse? Does Johns truck have a manual transmission? I can see where an auto would probably mask this problem, a manual can load the engine much harder then an auto.



Sorry to drag this back up, but Bill and I got to talking about this the other day. I wanted some more info in solving this problem.



Michael

 

[Greenleaf]

In a word.........

No.



You need to spend some time on the phone with Paul @ HTT.



Yes, John has a manual transmission in his 1993 W 250. He installed the HTT upgrade onto his OEM unit. It consisted of nothing more than comp. housing and a 60mm comp. wheel. He simply bolted it on. Nothing more.



Told me it surges when pulling a loaded trailer over hill & dale in WV. The boost needle bounces. I believe it was a cheap upgrade. I'd opt for the higher flow 60mm wheel along with a balance. Then again, it may be nothing more than the fact he had, at that time, a non-gated 14 exhaust housing. It could have added to the problem.



The larger(fatter/wider) 60mm compressor requires about an $80. 00 machine charge to increase the deapth of the backing plate. It's NOT a bolt on upgrade. I also have an PDR HX series turbo that HTT modified, so it's not apples to apples either.

 

[Jgolden]

"I'll take a broader, more usable powerband over peak numbers any day"



I think thats what I got out of adding a 58mm compressor wheel(stock was 50mm) and the housing for it. (The housing has a groove/ring cut into it but I don't know if that is the same type of groove mentioned above. ) The air intake is now 4" to the turbo, The turbo to intake crossover is 2. 5" all the way. Exhaust housing is stock 18.



When talking to HTT about wheel size they would repeat that "you don't want to go too big". Naturallly it depends on how far up the HP scale you want to go, so they can't tell you what is too big. (The old joke, "who you gonna please with that little thing?", applies here; the answer is, "me". )

I don't pretend to have a lot of experience on the topic but here are my thoughts on results. (sig shows details, I am always fully loaded. )

Running the same road loop used the first day I owned the rig. 2 lane highway with a long hill.

Before the turbo upgrade the powerband was pretty narrow, early onset of max EGT. Now I don't see any difference in spool, maybe a little sooner (?) Boost builds quicker,tops a little over 20#. Could get a bit higher before, maybe the start of "surge" holds it back?

On a long hill, holds power much longer. Egt does not hit 900 (post turbo) until rpm drops, then it would/could take off. Level road more power right up to max speed with slow egt climb. EGT drops fast when you let off.

Still have more fuel than I can use on hills, but over all much better. More RPM's would be good, as well as a way to cool top egt's.

50mm to 58mm made a differencen no idea what 60mm would have done.

Need to take a longer ride to get a clear picture, so far so good.

Thanks for all past advice.