Turbo Sneezeing or Woofing?

[LaserBob]

Just a question about the sneezeing sound that a turbo makes when you let off the throttle quickly. What is the cause and is it hard on the life of the shaft in the turbo? I have an idea that the sound is nearly always there, but not loud enough for most to hear. I have had a new inlet venturi piece made for my turbo inlet and the woofing has increased noticeably. Does anyone have the technical knowledge to enlighten me?

Thanks Bob

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95 2500 auto reg cab TST # 12 (a friend had this one extra)for now. Wastegate gets No signal. 136K,Just installed DTT VB & Convertor,(2/22/01)WOW! Bob Berends

 

[LSMITH]

Bob, that woofing sound is the pressurized air in the intake system stopping and spinning the turbine wheels backwards for a second when you let off quickly. Letting off takes away the exhuast gasses that were driving the turbo and making the boost pressure. The exhuast gasses will build up and overcome the pressure in the intake stopping the wheels again and spinning them the other (proper) direction. This will happen a couple of times until the pressures are equalized. Let off slowly if you can and this won't happen. It is very hard on the turbo. Think about the stress on the turbine shaft when it is spinning insane thousands of RPM then is stopped and spun the other way in a very short period of time, only to have this repeated until the pressures are down. I have heard of several HX-40's breaking the shaft when this happens and the turbo was making over 50 PSI. Never heard of an HX-35 breaking though.

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99 2500 QC 4X4 AUTO SB 24V LARAMIE SLT 3. 5 LSD 285-75-16'S SPA Boost/EGT Everything but leather NRA Member Great Lakes TDR Member

 

[LSMITH]

The noise is normal, and there is no cure other than lifting slowly which isn't always possible. You will hear it more often on an auto truck, because the RPM drops almost instantly. With a stock turbo I wouldn't worry about hurting anything if I was under 30 PSI, but I have no fact to back that up, JMHO.

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99 2500 QC 4X4 AUTO SB 24V LARAMIE SLT 3. 5 LSD 285-75-16'S SPA Boost/EGT Everything but leather NRA Member Great Lakes TDR Member

 

[illflem]

I've had the most problem with it when tapping the brake to disengage the cruise, I've since learned to keep my foot on the throttle while disengaging. It sure sounds like it would do damage.

 

[drawson]

I noticed the same thing after putting in my Silencer ring replacement cone. Ta first i thought it was the cone moving but it took it back out and the noise is till there just much queiter.

The noise is a good reminder not to back out of the throttle too fast.

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EAT'M UP
97 2500 Club 4X4 3. 54, Forrest Green/Driftwood, LSD 5 speed, & Psychotty Air System, TST #11, 370 HP injectors, timing at 16 deg. , 16CM2 housing, AFC spring kit, TST EGT gauge & 0-60 boost gauge in A Pillar, Cat-be-gone, 4" Dynomax Bullet muffler, Crome 4" turn down, 2 Electric Fans, One inside/ One out front, AmsOil Through out, Geno's trans filter kit, AmsOil Bypass system, Lund Winter front, Leer Cab Level Shell Driftwood , 255/85R16, South Bend's Hypo Clutch*NRA/USPSA member and proud of it*

 

[SlyBones]

Is there any cure for this, or just simply just just dont do it?

I have had my truck for 7mo now, and only discovered this noise a few weeks ago. Was trying to accelerate, was around 12# boost, and someone pulled out in front of me. Had to let off and jam the brakes. Made this loud noise. I dont mean barely audible or needed to strain to hear it. I mean anything over 10-12# and lift quickly and any one in the truck can hear it easily, even over the stereo ( depending on volume of course ).

So is this normal or is this excessive noise and should I check into cures?

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1997 2500 4x4, CC, Auto, 3. 54 LSD, 66K, Everything inc Leather, K&N, 4" BD cat-back, otherwise stock, Isspro Gauges(3), 285/75/16 on Alcola's, RS9000's, Canopy, BedLiner, and tons more.

 

[CumminsPower98]

Mine makes this noise just about every time I shift (unless I'm taking it really easy) so how on earth can you avoid it? Just no speed shifting? Maybe don't let off the throtle as much? I have not yet bombed my truck so probably no worries. All I have done is an air filter, exhaust, and backed off the star wheel.

Mark

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Red '98 12valve 2500 4X4 Quad Cab, Long Bed, SLT, 5-spd Manual, 3. 54, Dana 80 Rear,Camper/Tow pkg, 33x12. 50x16. 5, Rancho RS9000 shocks, straight piped, silencer ring hanging in shop, Yet to be Bombed, 68K+ miles.

 

[LaserBob]

Thanks for the ideas. I am still not convinced that this sneezeing is bad for the turbo shaft. I think that we only notice it when we get better breathing ability or change the flow of the air into the turbo inlet. If, indeed, the pressure is making the turbo spin backwards when you back off, how many shafts would you 5spd guys have to change from shifting? Now I am not trying to pick a fight, but think about it, what have I done different? I just put a free flowing air cleaner on and got some of the noise. I now added a velocity stack to the inlet and there is more sneezeing again. I have watched the throttle position and the boost pressure very carefully and I am still studying the relationship of the two. If you have about 12 to 16 lbs of boost and feather the peddle, you can hear a flutter in the air flow. A slight increase in peddle will make it go away as will a slight decrease in the peddle. There is more to this than we (or I) now know about this. I will update you when I get more info. Just my thoughts.

Bob

 

[B.G. Smith]

I think you are correct on the shaft not spinning backwards LaserBob. Large centrifugal air compressors will do the same thing, surge, when the discharge pressure gets too high or the suction is restricted, the air or gas stops flowing and surges back through the compressor. I have seen it happen many times but never saw the turbine or motor driving the machine slow down let alone run backwards. The big units will sometimes wreck because of pipe movement. When you are hooked up and making boost the turbine is probably turning 100,000 rpm, if it could stop and reverse that fast, yes it might break the shaft but I don't think that is happening. bg

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White 99 3500, QC, 3:55, auto. most options except leather, Line-X bed liner, fiberglass running boards Rancho 9000s, bug shield and window vents, black vented 5th wheel tailgate, 110 gal. aux. fuel tank.