bark stops here!

[DCreed]

I believe I've got an answer to a nagging problem of the turbo diesel world. A simple low cost possibly d. i. y. way to eliminate turbo bark and the associated failures! What is bark ? Bark happens when the turbo is suppling boost pressure and the engine doesn't need it; i. e: when you shift or lift suddenly off the throttle. The resulting back pressure can't get out, so it slows/stops the turbo compressor, putting strain on the bearings and in some cases shearing the shaft !!#@$%! Gas engines use a BOV or blow off valve to cure this. It simply opens/vents boost from the vacuum created behind a closed throttle plate. Unfortunately diesels aren't quite that simple so untill now we've had to deal with it or shell out the $$$. If bark isn't a problem for you maybe you'd just like the swoosh sound it makes or the increased spool between gears. Anyway if I get a decent response here for it, I'll post a schematic and some pics . Maybe a kit for those not inclined to D. I. Y. Hope to hear from y'all ! Carl.

 

[Forrest Nearing]

just use a solenoid and use vac from the vac pump for the top of the BOV. trigger w/ a hobbs and momentary in series... either throttle all the way off or clutch in.

 

[DCreed]

doesnt work ... bovs cant handle 30+psi never mind 75+! also if u did it that way it would be open at idle sucking dirt!

 

[Forrest Nearing]

how does BD do it using a Tial BOV then? you run boost on top to keep it closed, then either dump that via solenoid or if you want to get crafty, run solenoid vac to the top. trigger the solenoid w/ a Hobbs and or micro.

 

[DCreed]

my set-up cost less than the tial alone!

 

[Nate]

Let's see what you have Oo.

 

[DCreed]

Go here to see:



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[TAbbott]

"Bark happens when the turbo is suppling boost pressure and the engine doesn't need it; i. e: when you shift or lift suddenly off the throttle. The resulting back pressure can't get out, so it slows/stops the turbo compressor, putting strain on the bearings and in some cases shearing the shaft !!"



I don't understand this line of thinking. It might be accurate if there were a throttle plate in a diesel, but there isn't. The highly boosted air "can get out" just as well in the circumstance noted as at any other time. Makes me think this explanation might be flawed.



I think the "bark" as it's commonly referred to, is caused when the pressure in the intake manifold exceeds the pressure inside the cylinder, slightly lifting the intake valves off their seats, allowing the rapidly rising cylinder pressure (and its accompanying noise) to leak back into the intake tract as the piston comes up on TDC prior to the valve spring and the increasing pressure slapping the valve closed.



That is the explanation that was given to me by Detroit Diesel mechanics when the Series 60 engines were in early production, back in 1988 or so, and were making the same sorts of noises on shifts if the boost was high and the throttle suddenly cut, reducing engine fueling to zero (instantly reducing cylinder pressure). This explanation at least makes sense given the way a diesel engine operates.

 

[TBurow]

wouldn't it be easier to just use a pneumatic solenoid hooked up to a 5 psi pressure switch in the intake and a micro switch on the throttle so that when the throttle is closed and pressure is greater than 5psi the valve opens and dumps the excess air pressure into either the air cleaner box or a small filter?

simple and very effective, the time it takes to open a fast acting pneumatic solenoid is in the hundreths of a secound. hey maybe i should make theese and sell them, dam i just gave away my million dollar idea.

 

[DCreed]

go for it ! thats how i got here !

 

[BILLVO]

how does BD do it using a Tial BOV then? you run boost on top to keep it closed, then either dump that via solenoid or if you want to get crafty, run solenoid vac to the top. trigger the solenoid w/ a Hobbs and or micro.

Our local BD dealer doesn't even use them anymore. He claims they are not fast enough. He has several trucks with twins that have had them on and they still trashed turbos. He has had a few stick open also. He will not even sell them anymore.

 

[DCreed]

"Bark happens when the turbo is suppling boost pressure and the engine doesn't need it; i. e: when you shift or lift suddenly off the throttle. The resulting back pressure can't get out, so it slows/stops the turbo compressor, putting strain on the bearings and in some cases shearing the shaft !!"



I don't understand this line of thinking. It might be accurate if there were a throttle plate in a diesel, but there isn't. The highly boosted air "can get out" just as well in the circumstance noted as at any other time. Makes me think this explanation might be flawed.



I think the "bark" as it's commonly referred to, is caused when the pressure in the intake manifold exceeds the pressure inside the cylinder, slightly lifting the intake valves off their seats, allowing the rapidly rising cylinder pressure (and its accompanying noise) to leak back into the intake tract as the piston comes up on TDC prior to the valve spring and the increasing pressure slapping the valve closed.



That is the explanation that was given to me by Detroit Diesel mechanics when the Series 60 engines were in early production, back in 1988 or so, and were making the same sorts of noises on shifts if the boost was high and the throttle suddenly cut, reducing engine fueling to zero (instantly reducing cylinder pressure). This explanation at least makes sense given the way a diesel engine operates.

please read FAQ on bark in holset thread, good up to date info!

 

[NoSeeUm]

I think the "bark" as it's commonly referred to, is caused when the pressure in the intake manifold exceeds the pressure inside the cylinder, slightly lifting the intake valves off their seats, allowing the rapidly rising cylinder pressure (and its accompanying noise) to leak back into the intake tract as the piston comes up on TDC prior to the valve spring and the increasing pressure slapping the valve closed.

The explantion above is pretty much spot on. I am not sure what you are referencing is talking apples to apples in this case.



It is not the throttle plate specifically, because diesels don't have one. It is the sudden drop in engine RPM. Essentially, the engine can go from lets say from consuming 900 CFM to 300 CFM rather quickly during shifts. This is under conditions of high RPM high boost. Basically the same thing as what would occur with a thottle plate closing down, but much less apparent in the vast majority of cases. Ussually it takes a bigger aftermarket turbo running higher boost. I could not bark my HX35 and I definately tried, although indirectly.



Here (click the technical tab and scroll down) is a picture of a compressor map. If you are not familiar and to make it simple, the vertical axis is essentially boost pressure and the horizontal axis is essentially engine RPM. Any point above and to the left of the line left of the shade area (evelope) is where barks can occur. The left line is called the surge line. With a severe surge condition you get a pretty loud "barking noise", hence the name.



Jim

 

[Mhannink]

bark comes from the boost pressure being higher then the drive pressure. when you spooling up your turbo the drive pressure rises on the exhaust side that spools the turbo and builds boost. when you back out of the throttle hard the drive pressure drops instantly since its not being fueled and the combustion temps arent as high. the boost however does not fall off as fast as the drive pressure. the resulting change in pressures tries to spin the tubro backwards as the boost looks for escape. the boost goes the only place it can. back out the way it came in through the turbo. trying to spin it backwards slowing the turbo abruplty(sp?) creating a bark and sometimes snapping turbo shafts and causing other damage

 

[DCreed]

thank you for your input. thats basically correct. but otherpeople cant see the forest through the trees! the whole point was to say the valve relieves the problem, but i guess some just gotta poke!

 

[swmnkdinthervr]

Ussually it takes a bigger aftermarket turbo running higher boost. I could not bark my HX35 and I definately tried, although indirectly.





Jim

I've barked mine a few times... none intentionally... with only the mods below...

 

[Vaughn MacKenzie]

I have wondered about installing some sort of large check valve at the compressor discharge so the moment drive pressure drops it will close and prevent back-surge. It would have to be carefully engineered to minimize any airflow restriction set up by turbulence caused by the check valve. Here's a crude drawing I made of one with a checkvalve with an internal spring mounted midair within a bullet piece. The outer edge of the checkvalve has softer material that will help catch backflow to pull it over the opening and also serve to seal the opening.



No matter how well designed this will still present some restriction to airflow, but the benefit is if you shift fast you can still preserve some of your accumulated boost to dive into the next gear

 

[DCreed]

could be easily done with flapper valve... never thought of trying ! youll have to tell us how it works!!