Turbo Bark I want to know more!

[RBallard]

Looking through some of the past messages I have come across the term "Turbo Bark" and I want to know more. This is obviously my first Turbo Diesel and I have owned it since June 2001. I haven't towed or hauled anything where more than a 1-1/2 tons but I do drive it hard, it's my nature. The truck is an April 2001 ETH and I am currently running 4" exhaust straight with the BHAF, other than that, the motor is stock. I guess it may be my stupidity but I always thought the bark occurred when the waste gate dumped and since I have always heard it in the big rigs I never thought about any damage occurring. I now have roughly 17,000 miles on it and I know on many occasions I run the pedal to the floor as I shift through the gears, of course I let off the throttle when I depress the clutch so I do loose the manifold pressure and I do get the bark but it always sounded as if it came from the exhaust and not under the hood.



My questions are first, why isn't there anything listed in the owner’s manual or in the service manual. What's the solution? It almost sounds as if a check valve would solve the problem and if it's as simple as that why doesn't Cummins supply the motor with such a device. I would think with a manual transmission, it almost always barks. In 2nd I shift with 5# boost, 3rd might have 10#. I know 4 and 5 I have shifted at 15#-23# a check valve. What I have noticed on the boost gauge was a rapid drop from 23# to 10# before I am in the next gear.



Searching around the internet I have found turbo blow off valves and I do not fully understand them. Most of the units I have seen vent to the atmosphere. What keeps them from opening under pressure? Would you want to open to atmosphere or would you want a check which could essential maintain boost to a certain degree and keep the pressure from exiting the inlet.



I would appreciate any information this group can provide.



Thank you,

 

[Bad340fish]

Mine has only really barked on me once... and thats when I let out at 25psi in 4th gear coming out of a burnout(had to show up a gasser)



A friend of mine had a 12V truck that kept the EGT and Boost gauges pegged on a regular basis when looking for mustangs on the local cruise. His has barked so bad before that we have pulled over checked to make sure the air box was still there. WOT 5th gear 35psi guage pegged between the OOs on boost and letting off real hard because the road is getting short makes them bark real loud!



I don't know how easy it would be to find a blowoff valve that will hold up to the high PSI the CTD uses. And the fact that most of them work off vacuum makes them not work to good for the diesel world.

Clark

 

[Deezul1]

I am running 40lbs boost and I get the bark anytime I let off with the boost up. I have learned to not let clear off when shifting and it lessens or eliminates it. I believe that the bark is when the turbo try to reverse at sudden loss of boost but am not real clear on this and hope someone with more knowledge than I chimes in. I do know you can hurt your turbo by doing this.

 

[Bad340fish]

After reading your signature I don't think your hearing a bark. The big exhaust you have is going to allow you to hear the turbo alot more. I notice it through the pipe with slider open alot. Its more of a whhhooooossssh sound isn't it?? A turbo bark is loud and harsh sounding. Like i mentioned in the above post mine has only done it once and I drive the hell out of my truck.

Just a thought

Clark

 

[Briar Hopper]

You definitely don't want to bark that puppy. It can, and has, snapped the shaft on a few turbos. So they say. Some turbos are weaker than others. You don't know you have a weak one till it breaks.

 

[RBallard]

Maybe I am getting the terms confused, Bad340fish. The sound I hear is more like the whoosh, like a blast of air with the turbo whistle. I am sure the noise is comming from the tail pipe and the toned changed when I removed the muffler.



Does the bark sound like a spun bearing? There is a southern states big truck across the road from me and when he shifts, his turbo sounds like it has bad bearings. Could this be the "bark".

 

[Deezul1]

It sounds like a BIG dog giving one bark, once you hear it you will know. I didnt hear it till my boost got up around 32 or so, below that I never heard it all.

 

[LSMITH]

A good solid turbo bark will make a WOOF WOOF woof sound about as fast as you can say it in a decending tone. It sounds like it is coming from the airbox as in fact it is. The more boost you have on it the louder it will be, and you will get more woof's out of it. It is the turbo being stopped and spun backwards by the compressed air in the intake system as mentioned earlier. It is bad, and you should avoid it. Hope this helps.

 

[RustyJC]

The actual engineering term is not "bark", but compressor surge or stall. The noise is caused by airflow reversal through the compressor. Since the diesel engine, unlike a gasser, does not have a throttle valve in the intake system, backing off the accelerator pedal does not immediately cause a high head/low flow condition that is the classic cause of compressor surge. Rather, chopping the fuel causes the turbocharger to lose drive energy on the turbine side, so the compressor impeller begins to slow down. With the impeller decelerating, since it is a dynamic rather than a positive displacement air compressor, it cannot maintain the head (high boost pressure) seen at the compressor outlet, and the airflow actually reverses through the compressor section of the turbocharger (Note: the rotation of the turbocharger rotor itself does not reverse - there's too much rotational inertia in the rotor assembly for that to happen!) This reversal of airflow unloads the impeller, shaft and turbine of the turbocharger. Once the excess head has been dumped, the turbocharger compressor will pressurize the intake system once again, but if the turbocharger is still decelerating, its speed will fall to a point where it once again cannot maintain the head it has created, and flow reversal will occur again. This process can continue to repeat itself as the turbo continues to decelerate - each time it does, the "whoomp" is audible. The repeated loading and unloading of the compressor impeller, shaft and turbine can cause cyclic fatigue failures.



Rusty

 

[Ramafid]

I get the bark nearly every time I back off the throttle at high boost. I try hard not to do it but sometimes just don't have a choice. I never had the problem until I upped the boost to 29 lbs. Last thing I need to happen is have the turbo grenade.

 

[John_P]

Rusty:



Excellent post and explanation!

Thanks!



---------

John_P

 

[John]

Originally posted by Briar Hopper

You definitely don't want to bark that puppy. It can, and has, snapped the shaft on a few turbos. So they say. Some turbos are weaker than others.

Most noteably HX40s.



That's one of the reasons Piers' modified HX35 Super Turbos are stronger units.



Excellent explanation Rusty!

 

[3dracer]

The woosh of air is normal and is louder when it is straight piped. The loud and fast barks that do descend in volume is not normal. Exactly what Randy said. There was a truck at the Shied event in Terre Haute that pulled and when he got to the end he lifted off of the throttle at once and it barked once real fast and that was it. We later heard that he popped the turbo. It is a series of high pitched barks real fast and goes down in volume. But I did learn something here tho, I didn't know it was that harmful. Glad to here this iguess. Helpfull though.

 

[Wirenut]

Interesting, I've never heard this. I am at 37 psi and I'm wide open all day long. Must have a good turbo but if it breaks... . hmmm, good excuse to get a bigger one?

 

[3dracer]

The only time I heard it was when a friend of mine was trying to brake torque and when he let off all at once, I heard it then. Hard to explain the sound of it without making the sound. Deffinately not a good sound tho. Scared us at first. . The best way to describe it is at a Tractor Pull, with the smokers . Sometimes when they are in the middle of a pull it will do that noise. Or alot of times at the end. You are guarenteed to hear it at least once.

 

[John]

The barking can occur in almost any modified CTD, not just sled pullers or drag racers or with performance turbos. Just for instance; you are ascending a grade up a mountain pass with trailer in tow... 25 psi boost in 1:1 gear... everything's cool until some moron decides to abrubtly change lanes... into your lane... right in front of you! You immediately get off the throttle and are quickly looking for the brakes. Before you can get your foot on the brake pedal the dog already beat you with... bark, bark, bark!



I may be wrong but, I've never heard of a broken shaft in any Holset turbo used on a Dodge Ram other than the HX40s.

 

[Diesel Freak]

I barked my turbo once. This was when my stock clutch slipped the first time and I side steeped the loud pedal at over 30 PSI. Sounded like my airbox blew up . I definately will not do that again!

 

[Hummin Cummins]

I havent heard mine bark yet, but without gauges installed yet I may not be getting enough boost to cause it. I'm straight piped and I hear the whooosh all the time heh heh heh. Cant wait till the ol income tax check gets here

 

[HillCountrykid]

Another member was nice enough to let me take his truck for a spin and I was nice enough to bark his turbo. He was nice about it and explaned what happened and I said "That was'nt good for it, was it?" He told me no. It was an HX-40. I'm glad I did'nt tear anything up on his truck after he was kind enough to let me drive it.



Give me a ball bearing and I'll tear it up with a rubber hammer.



Brian

 

[RBallard]

Thanks to all the fellow members for the posts.



3D Racer the light bulb just came on!! I have heard the bark year after year and never knew it. Heck, I even have it on digital video. I go to the local tractor pulls and the turbo diesel tractors have always bark at the end of thier pull. I distincly remember the noise, I never placed the two together.



Thanks again,



and many thanks to Rusty for such a good explanantion.



Bob