Blow-off Valve

[2stangs8689]

TT... Thats what scares me is the sudden difference is spinning the wheels go through. I want to drop down to a smaller housing and put a waste gate on for quicker spooling, but i can imagine that making it worse..

Another great reason to run a WG. A WG gives you control over the hotside turbine, what you don't want the wheel to see is bled off out the valve and into the DP.

 

[V-Ref]

turboshaft engine

I strongly suspect the "bark" heard on a turbocharger, is the same phenomenon referred to in turboshaft engines as "compressor stall", but without a turbo rpm gauge, I'm hesitant to say it's absolutely the same thing.

FWIW, when the compressor section of a turboshaft engine (usually several axial stages, and then one centrifugal stage) encounters "compressor stall", it's referring the blades on the compressor wheel encountering an aerodynamic stall condition(i.e. exceeding it's critical angle of attack for a given load factor), not a sudden stoppage of rotational rpm...however as a byproduct of turbulent or reverse flow through both the compressor section and power turbine, and the corresponding inefficient combustion of the fuel..... there are fluctuations in rpm, and often in increase in engine exhaust gas temperatures. Most of the "newer" Digitally controlled engines will recognize this condition, and pull fuel immediately, limiting the action required by the crew....some of the "older" mechanical designs, required manipulation of both the power available/power demanded portions of the fuel controls on those engines in order to exit the compressor stall condition. Not certain this means a hill of beans, side of fries, or a cup of STFU...thought I'd share anyways..:toast:

To think that we could buy a turbo for $800-2500, that had the metallurgy to withstand a sudden stoppage and then re-accelaration, especially when you consider the rpms of these turbos....I'd be impressed.

But without a turbo rpm gauge...tough to say for an absolute on what's really going on in there. Certainly it can't be good for extending the life of the turbo IMHO. I've certainly done my share of it. :morons:

Maybe there's someone out there with a gauge, that could give us some insight on the change in turbo rpm when encountering a surge condition....I'm curious now.

 

[2stangs8689]

:whs:

 

[Big Bore]

I strongly suspect the "bark" heard on a turbocharger, is the same phenomenon referred to in turboshaft engines as "compressor stall", but without a turbo rpm gauge, I'm hesitant to say it's absolutely the same thing.

FWIW, when the compressor section of a turboshaft engine (usually several axial stages, and then one centrifugal stage) encounters "compressor stall", it's referring the blades on the compressor wheel encountering an aerodynamic stall condition(i.e. exceeding it's critical angle of attack for a given load factor), not a sudden stoppage of rotational rpm...however as a byproduct of turbulent or reverse flow through both the compressor section and power turbine, and the corresponding inefficient combustion of the fuel..... there are fluctuations in rpm, and often in increase in engine exhaust gas temperatures. Most of the "newer" Digitally controlled engines will recognize this condition, and pull fuel immediately, limiting the action required by the crew....some of the "older" mechanical designs, required manipulation of both the power available/power demanded portions of the fuel controls on those engines in order to exit the compressor stall condition. Not certain this means a hill of beans, side of fries, or a cup of STFU...thought I'd share anyways..:toast:

To think that we could buy a turbo for $800-2500, that had the metallurgy to withstand a sudden stoppage and then re-accelaration, especially when you consider the rpms of these turbos....I'd be impressed.

But without a turbo rpm gauge...tough to say for an absolute on what's really going on in there. Certainly it can't be good for extending the life of the turbo IMHO. I've certainly done my share of it. :morons:

Maybe there's someone out there with a gauge, that could give us some insight on the change in turbo rpm when encountering a surge condition....I'm curious now.

I read through all that and now I'm even more confused on the nomenclature. Is the "bark" from the turbo "stall", or "surge", or are those the same thing? I was under the impression surge was something that happened under heavy throttle, and the "bark" was "stall", as in the turbo was "stalling" because of the change (reduction) in exhaust velocity from an upshift, and the sound is the compressor wheels instantaneous slowdown against the intake air.

 

[V-Ref]

I read through all that and now I'm even more confused on the nomenclature. Is the "bark" from the turbo "stall", or "surge", or are those the same thing? I was under the impression surge was something that happened under heavy throttle, and the "bark" was "stall", as in the turbo was "stalling" because of the change (reduction) in exhaust velocity from an upshift, and the sound is the compressor wheels instantaneous slowdown against the intake air.

Hey...since I created the chaos here....I feel compelled to try and make it worse! riest:

This is all JMHO...without a turbo rpm gauge, and a boost/vacuum reference installed pre/post compressor...I don't know enough to say my opinion is worth anymore then what it cost me to post it.

The thing commonly referred to as "surge", the "choo choo choo" sound the stock turbo makes when you push it beyonds it's happy place....is just a bunch of miniature versions of the big "bark" you hear after a high boost/high drive scenario, and you suddenly remove all the drive pressure by pulling your feet away from the floor. IMHO they are both "compressor stall", just a less aggravated condition/version of the same phenomenon.

I strongly suspect, that by plotting the data points from a boost guage and a turbo rpm gauge, both the "choo choo choo" and the "bark" would plot to the left and north of the surge line, on that respective turbochargers compressor map.

I'm gonna call that Jose fella @ Forced Inductions...see if he's got 2 minutes to answer that question....

Or maybe we can lure in a brave smart guy from PSA, to post up, and keep us all on track....I know there's somebody(s) reading this thread that knows the absolute answer... oke:

 

[TARM]

That is what I have come to as well.

The one where you suddenly let off under heavy boost is a long sustained action. Then you have the turkey gobble from pushing a turbo and overspeeding it while on the throttle is successive shorter version. They are both caused by the turbine wheel spinning faster than the exhaust can maintain or steadily maintain depending on the version you are speaking of. The difference is in the severity of the stress created. The surge (turkey gobble) is more damaging as its multiple shock loads both ways. Where stall is but one but longer event in only one direction and not multiplied by a repetitious pattern of boost and stall, boost and stall unload full load.


Honestly looking at how many are not even running waste gates when most should be the number willing to take this beyond talk is likely very limited. But I think its a very good idea and something I would be willing to add to my to do list.

 

[Vader's Fury]

Glad to see I am not the only one that thinks this is an issue. Not as great as other issues we have but still an issue. Some good info in here about turbo surge and stall.

I didn't think about using a turbo RPM gauge to see if this does make any difference in how the turbo reacts under different load situation. Anyone have any experience installing one of these? Looks like I should add this to the list to be done when I install the BOV to see if it actually does make a difference.

 

[6.0dirtworker]

If you are going to put a bov on, you always want it downstream of the cac. I just know the let off is horrible for what has been stated and the thrust bearings too, which I thought were only in sleeve bearing chargers. Are thrusts in any other turbos?

Isint this a surge? If not what is it, I know that turbo isn't happy though.
http://m.youtube.com/index?desktop_uri=/&gl=US#/watch?v=nCj6Spwl1CU
Sorry I'm having trouble linking the vid from my phone.

 

[Vader's Fury]

If you are going to put a bov on, you always want it downstream of the cac.

Can you explain more as to why you say this? I would have thought that, for a gas motor, this is where you would want it since it would be close to the throttle valve.

For our application we are trying to prevent the turbo from "barking" so I figured that placing it close to the outlet of the turbo would be more practical.

I have no experience with it either way, just what I was thinking.

 

[6.0dirtworker]

Sorry, I meant before the after turbo before intercooler downstream. I remember garrett stating that a while back. Im not sure if this is right but this is how I think of it. yeah you want it closest to the turbo as possible. When you blip the throttle abruptly, a vaccum occurs and tries dispersing the air through the intake. So you dont want the bov close to the manifold on the pipe after the intercooler, you want it before the cooler to get all the air out of the tubing. Because when it activates its only relieving the air that is coming from manifold back to bov because of the vaccum, and that wouldnt get rid of the air in the pipes pre-bov. So your still having air vaccum through the comp. I doubt thats right but if someone could let us know thatd be great lol.