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Sounds cool. What makes it happen?

mohawkmike82

mohawkmike82

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Cleveland, Ohio
Just wondering why a lot of the newer engines chug down like this when you step off the throttle. I have searched high and low to try to find a reason and I cant find anything. The only thing I can think of is that a much higher boost level may cause the waste gate to oscillate? Or is this a different type of boost control? Anyone ever hear a 6.2/6.5 do it?

http://www.youtube.com/watch?v=FmECokBPbrA
 
I have no idea but when I see someone with trucks like this hooked bumper to bumper.....all I can think is "what a moron!" Must be some spoiled brat that spent daddy's money to buy the truck.....and daddy's money can fix it when it breaks.

lol
 
Yeah its ridiculous to flog your equipment like that. And that's not what I'm into just for the record. This vid just lets you hear a good example of the sound I'm talking about.
 
That sounds like turbo bark I think. The turbo builds a boost pressure and the intercooler stores the boost when you let off the fuel the air pressure wants to push back through the turbo inlet which fights the exhaust back pressure and it "barks" and huffs loudly.

Its not good for the turbo. You should only hear it doing something like this where you load and unload kinda quick. You have to have load and fuel to make boost ie chaining 2 trucks together and loading it up.You shouldn't hear it normal driving.

The 6.5 doesn't build that much boost or have a large storage volume either. Plus newer trucks can have variable timing injection and most importantly variable turbo such that boost builds quicker than the typical 6.5.
 
It's either turbo compressor surge, or turbo compressor surge in a system w/ a blow-off valve set to contain notably higher boost pressure than was achieved when he let off.

When looking at turbo compressor maps, the line/limit on the left side is the surge line. The compressor can't operate at the boost level/mass airflow (combination of) conditions to the left of the surge line & becomes unstable. It's very hard on turbo thrust (& to a lesser extent) journal bearings.

On high boost systems using a blow-off valve set to contain say 30+ psi of boost, they often don't blow open cleanly if the engine's just run up to a fraction of the blow-off valve's set point. On a turbo gasser (w/ throttle blade), run up to 30 psi in 1st gear - turbo spooled, let off throttle to shift - throttle blades go shut, turbo's still spooled...airflow can't go anywhere, pressure begins to go over 30 psi & the blow-off valve pops open & vents the airflow so the compressor wheel doesn't suddenly see much higher pressures & stall/cavitate.

On the same setup more casually run up to just 15 psi, upon shifting/throttle blades shut - the turbo isn't spooled as fast. So the BOV opens more lazily/slowly, but often shuts/opens - oscillating or chattering.
 
Chevy Dooley said:
It could be a turbo guard (blow-off valve)
I have blow-off on my other car.Saves the turbo and dont have to wait
for boost when I change gear.
A little bit different for dieselturbo. A LOT Different

http://www.dieselperformance.com/index.php/product/index/10P
Click to expand...


Chevy Dually

BOVs are required in gasser engine as they have a throttle plate that goes closed on throttle let off, and that built boost needs to go somewhere so BOV vents it.

Normally they are not really necessary in Diesel as no throttle plate to close off but as Smithfield sometimes the plumbing in performance Diesels that are high boosting you may need a BOV, but most turbo Diesels don't need a BOV,

I'm curious to your not having to wait for boost comment, why are you waiting for boost to make gear changes, even the 6.5 does not need for that to happen?

When I'm racing it I might stage a little to get some bottom end spool then just let it run thru the gears @ WOT. You have a manual trans ?
 
I know it is a big difference and that diesels dont have a trottle plate.
I have never heard that sound from a diesel engine before but it sounds just the same
as my Calibra turbo 2.0 16V. That turbo have a kind of recycling BOV oem wich dont
dump air. BOV I got now does.
I dont race with it or changes gear with wot. Its a 6 speed manual.
 
Nothing wrong with having fun. I buy old vehicles and modify them to crash them into other vehicles, is that a waste, sure but its fun as hell. If theres money on the line its just like anything else.
 
buddy said:
Nothing wrong with having fun. I buy old vehicles and modify them to crash them into other vehicles, is that a waste, sure but its fun as hell. If theres money on the line its just like anything else.
Click to expand...

Agree completely Buddy, reason I brought up what I did as a caution, some folks will try it just because of "coolness" factor without knowing it's not the best thing to do, some folks would think reflash & ATT are a waste
 
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