weird noise from turbo

[AVNote]

hey all, I've got a weird undescribeable noise coming from i think the turbo, when i step on it, and get her goin then realse the accellarator it makes some what of a sucking noise/rumble, everything looks fine under hood, all hoses attached, and check engine light does not come on. it only does this for a lil while, after running her hard for awhile it slowly stops doing that, anyone know what this might be ?



btw i got a 05 auto, with afe stage 2 intake.



thanks alot,





Andrew

 

[rrausch]

It sounds like you are describing "turbo bark". It happens when you suddenly push the accellerator pedal down which causes a lot of boost pressure, then you take your foot off of the acc. pedal, and all that boost has to go somewhere, so it goes backwards through the turbo. It's not good for the turbo at all.

 

[KBertetto]

It sounds like you are describing "turbo bark". It happens when you suddenly push the accellerator pedal down which causes a lot of boost pressure, then you take your foot off of the acc. pedal, and all that boost has to go somewhere, so it goes backwards through the turbo. It's not good for the turbo at all.

He's right... you should avoid causing this condition at all costs. It is possible to snap the shaft when it happens.



Bert

 

[AEzzo]

My truck started to make the same noise after i put the intake on. I thought it might be normal because truck was stock except for intake. Is it possible to bark a stock truck with a stock turbo? I figured i was hearing it because stock silencer was gone.

 

[RChamberlain]

but it sounds cool that is what my friend says on his and I told him it sounds exspensive

 

[AVNote]

how comes it does not do it when its in highest gear ?

 

[Vudumedman]

I get a strange sound from the turbo when I slowly move the pedal from coast to accelerate and back. It only happens above about 70 and sounds almost like a grinding. I don't think it is turbo bark, I don't hear it after heavy acceleration and sudden lift. If I gently play with the pedal at speed I can produce the sound at will. I have an 04. 5 QC 4X auto. Is this normal, it's done it since new and I now have over 50,000 miles.

 

[rbattelle]

It has nothing to do with what gear you're in and everything to do with the energy available in the exhaust relative to the power required to drive the compressor.



The bark happens much more often in automatic trucks. My theory is that at (or near) WOT on an automatic the sudden shift to the next gear and resultant abrupt drop in engine RPM manifest an immediate drop in exhaust energy. That energy loss, in turn, manifests insufficient power to continue driving the compressor at the current pressure ratio. The sudden drop in engine demand airflow, presumably resulting in greater backpressure in the intake, deteriorates the situation further. As a result, sudden severe compressor stall occurs; compressor RPM suddenly drops (perhaps to 0), and flow may actually reverse out of the turbo (although probably at very low energy, since people don't report their air filter assemblies blowing out when this happens).



The sudden change in RPM can prove fatal to the turbo - it is a condition to be avoided as far as possible. This can happen on stock or modified trucks. It is likely that Holset built the turbo strong enough to handle this abuse most of the time on stock vehicles.



-Ryan

 

[PHradecky]

Does the cummins have a bypass valve? Most turbo setups I have seen do. .

Have you ever listened to race cars with turbos they make a weird chirping sound when they shift. I think that is what you are hearing. The pressure has to go somewhere. .

 

[rbattelle]

Does the cummins have a bypass valve? Most turbo setups I have seen do. .

No. Probably most diesels don't. My guess is that it's because of the high knock-limited mean effective pressures of diesel engines. Force feed a gasser at the wrong moment and it'll explode on you.



-Ryan

 

[Boonieman]

Actually, the correct term for this "turbo bark" is called compressor surge. It's common in all centrigual compressors, which a turbo basically is. It is normally caused imostly n a high pressure, low flow condition. The higher the boost pressure without increasing total flow will cause the turbo to be more susceptible to surge. There are many, many articles on turbo surge on the internet. Each compressor or turbo has a "map" which can pretty accurately predict where surge will occur. Here's a starting point for the technically inclined:



http://www.turbocalculator.com/how-to-read.html