I'm finding it rather easy to bark the turbo on my truck. Can I put in a relief valve downstream of the turbo to prevent this? What pop-off pressure should it be set at?

 

what exactly is "barking" the turbo?

 

It's where you slam the throttle shut during high boost situations and the air gets backed up into the turbo. That's the basic idea.

 

To elaborate a little, the sound you hear is a "Wooofff" type noise. I think because the air has no where to go, it stops the spinning turbine suddenly. As you can imagine, this can wreak havoc within the turbo, as far as the shaft and turbine blades. BTW, I've never been able to bark my stock truck. I once had an '86 turbo T-Bird that was very easy to bark.

 

Actually, the correct term for "barking" a turbo is compressor surge or stall. There is far too much inertia in the turbocharger's impeller, shaft and turbine assembly to stop or reverse rotation. Rather, what happens is that the loss of fuel when the accelerator pedal is released results in an almost instantaneous loss of drive energy in the exhaust manifold. This causes the turbocharger rotor to slow. As it slows, the turbocharger compressor impeller can no longer produce the head (technically, discharge pressure minus suction pressure) required to keep the boost at whatever level is in the intake system. This results in a flow reversal from the pressurized intake system back through the impeller until the intake system pressure drops enough that the compressor can begin compressing air again. As the rotor continues to decelerate, this cycle can repeat itself several times before the system reaches equilibrium.

Rusty

 

Thanks Rusty. Your description was very easy to follow.

 

You're thinking of a BOV (Blow Off Valve). They are available a lot of places, but I don't know if they are diesel-specific.
These guys sell one that's diesel specific.
http://www.bd-power.com/ram/product....boGuard&tt=ram

The only reason I say diesel-specific is I'm not sure how this sucker is wired into the system if you just get any BOV. You don't want it to open until the turbo is going to bark. I suppose that's a combination of high boost and TPS reading idle?

Chris

 

I noticed my turbo barking after I had a few miles on the air filter. I replaced the filter and it hasn't done it since.
Bruce

 

Yep, a dirty air filter will drop the suction pressure to the turbo compressor impeller - this increases the head for a given amount of boost. More head at the same flow moves the compressor closer to its surge line, so it will be more prone to surge or "bark".

Rusty

 

Wot in 5th, i can slowly depress the pedal and still get it to "bark" not quite sure if i need a bigger one or what. I think the hx 35 is pretty much limited to like 35 pounds i think, im pushing 40 no problem with my mods. Intake filter is totally removed and run to the grill with a real fine hard screen on there. So restrictive air isnt my issue. my 2 cents thanks. By the way trucks for sale. E-mail if interested. Heatherschwartz1@hotmail.com

 

If you're running an HX35 at 40 PSIG, that's a LOT of head, which means (1.) it will be prone to surge, (2.) it's so far off its design performance map that compressor efficiency is terrible and you're generating a LOT of heat and (3.) I wouldn't even want to guess the turbo RPM required to produce 40 PSIG boost.

Ya pays yore money and ya takes yore chances.....

Rusty

 

If that truck truely has "No air filter" you may as well keep it. I sure wouldn't want it.

 

Well, I missed that. Aside from the fine lapping compound that's been ingested into the engine, I would bet that your turbo's compressor impeller has a fine layer of dirt on it, as well as possible erosion from the debris passing through it. That blows its efficiency out of the water which, in combination with the other factors I mentioned, will promote surge.

Rusty

 

i was able to take my stock hx35 to 47psi - lasted too......i just popped a head gasket!! Dirving it that hard, i had to be VERY careful how i backed off the throttle or it would bark

 

All I can say is that some people have gone over Niagara Falls and lived, too. That doesn't mean that everyone who tries it will. In fact, the odds are such (hoop stress in the impeller increases as the square of rim velocity, or rotating speed) that I'd rather not try it.

Rusty