[Biturbos4] All causes to turbo failures known?

Wed May 12 09:26:05 EDT 2004

I sort of miss my old K26 ('87 5KTQ). The car was chipped. After a 
little lag, that thing would build boost like nobody's business! That 
car had some serious thrust!
I never worried about that big old turbo going bad! I guess we're seeing 
Audi go the other way on "over-design".
Well, I'm still putting another 2.7t engined car in my stable in the 
next couple of months... just keep changing the oil and checking for 
leaks... :-)

David

Thus Spoke David Pramanik:

>I have to respectfully disagree with Keman's opinion of the K04 turbos.  The
>K04s have a larger compressor and turbine housing than the K03s do in
>addition to the larger compressor and turbine wheels.  Its only slightly
>larger, but it is larger.  Also the compressor outlet is larger and requires
>different (RS4) outlet piping.
>
>However, the most significant and important difference is in the shaft of
>the turbo itself.  The K04 has a reinforced shaft and should hold up much
>better than the K03 does.  Indeed the failure that you experienced with the
>shaft would most likely not happen due to its more robust design (in
>addition to the fact that it is made to run higher boost levels than the
>K03s are).
>
>The K03s appear to be somewhat underdesigned for the 2.7T motor, hence the
>failures.  Replacing them with K04s seems like a no-brainer to me, given
>that the cost is about the same and the K04s are much better suited to the
>engine.  And as of yet, no one has come up with a way to install any other
>turbochargers without relocating them and significantly altering the intake
>plumbing ($$$).
>
>-Dave Pramanik
>
>
>----- Original Message ----- 
>From: "Josef Hebenstreit" <josef.hebenstreit at hispeed.ch>
>To: "'Keman'" <keman at interwolf.net>; <biturbos4 at audifans.com>
>Sent: Tuesday, May 11, 2004 5:43 PM
>Subject: AW: [Biturbos4] All causes to turbo failures known?
>
>
>Hi all
>
>Just to give you a short reminder.
>My car: S4 2,7l 5V Biturbo, 265 hp, purchased 1999, chipped 1999 from
>265 to 310 hp, only chip-tuning no modification on the motor and exhaust
>system.
>I had a dramatic turbo failure before eastern. Just in short terms:
>accelerate -> big bang -> big cloud behind me -> my S4 lost all his oil
>within seconds. This was very dramatic for me and the guy behind me!
>
>Since then I am looking for the cause of the turbo failure. I am only
>willing to get my car repaired, if I know the cause.
>The newest information from my garage I got is that the turbine wheel or
>shaft has broken!
>
>The argument from the garage is quite convincing:
>S4 chipped (tuned) -> higher boost pressure -> higher turbo revolution
>-> higher mechanical stress -> turbo charger breakdown
>
>But then I am asking you: How can you drive 5 years and more then
>160.000 km with the same turbo chargers?
>Is it normal wear or is it boost pressure overload which caused the
>turbo failure?
>Does the boost pressure overload cause the seal to get leaky and give
>the oil the free way down the exhaust system?
>
>I have only a vage idee how boost control works:
>When you accelerate you reach at about 2500 rpm the maximum boost
>pressure which may be:
>1) untuned: 0.8 bar relative to air pressure
>2) tuned: 1.2 bar relative to air pressure
>without taking overboosting into account. May be overboosting adds
>additional 0.5 bar.
>
>To continue. Between 2500 rpm and 5000/6000 rpm the boost pressure stays
>constant by regulating the wastegate (bypass valve) in the exhaust
>system.
>If you take the next gear the rotational speed falls down to let's say
>4000 rpm and the bypass valve still keeps the boost pressure constant
>without changing the turbo charger's turbine speed simply by getting
>more exhaust gas to the turbine.
>
>Is this a feasible explanation for the boost control? Can anybody verify
>it?
>
>Has anybody precise date for the boost control of the K03 turbo charger?
>
>What is the maximum boost pressure both statically and dynamically I can
>apply to the turbo charger without risking a turbo failure? Especially
>the K03 turbo charger type.
>
>>From the tuning point of view what is the recommended boost pressure?
>
>If I have more precise data I can probably answer the question, whether
>the boost pressure was to high all over the time.
>
>Thanks,
>Joe
>
>___________
>
>
>-----Ursprüngliche Nachricht-----
>Von: Keman [mailto:keman at interwolf.net]
>Gesendet: Mittwoch, 5. Mai 2004 02:31
>An: Josef Hebenstreit; biturbos4 at audifans.com
>Betreff: Re: [Biturbos4] All causes to turbo failures known?
>
>  
>
>>>I have a S4 2,7 Biturbo/1999 and about 160.000 km. The chip-tuning
>>>pushed the performance to 310hp instead of 265hp. Even though I put
>>>my car to the service on a regular basis a turbo failure was
>>>inevitable!
>>>      
>>>
>
>What kind of failure?
>
>  
>
>>>1)    Wear
>>>      
>>>
>
>With infrequent oilchanges and poor quality oil, a turbos bearings can
>certainly wear out. They don't have to, Gerret for example will tell you
>that their turbos will outlast any engine you attach them to so long as
>nothing breaks that controls the turbo.
>
>  
>
>>>2)    Boost leak causes over-spinning of the turbo -> rpm to high ->
>>>mechanical breakdown
>>>      
>>>
>
>IMO there's your #1 cause. I highly recommend a good boost gauge .. I've
>had
>one since 10k miles, even though my S4 still isn't chipped.
>
>  
>
>>>3)    Defect or mal-functioning air-mass gauge causes ECU to read out
>>>lower values for the air-mass flow -> ECU responses with lower fuel
>>>injection -> lean fuel-air ratio -> high temperature on turbine of
>>>the turbo -> thermal breakdown
>>>      
>>>
>
>The O2 sensors detect this though and that's how you know the MAF is
>gone,
>there are codes for reaching the adaptive limit rich set and a quick
>glance
>at the MAF under heavy throttle shows much less grams/second measured
>than
>what is really coming in.
>
>  
>
>>>4)    Dump valve or bypass valve
>>>      
>>>
>
>When the bypass valves fail, they can cause an invisible boost leak
>since it
>can dump air back in front of the turbo, but still behind the MAF
>sensor.
>Aftermarket valves are a good idea.
>
>The wastegate diaphram can rupture, overspinning the turbo. Rare, but
>nothing is impossible. I've seen it once.
>
>  
>
>>>5)    Insufficient oil supply for the turbo - oil lines clogged or
>>>leaking
>>>      
>>>
>
>Crappy oil and infrequent changes, sure.
>
>  
>
>>>Normally the third case shouldn't be possible due to
>>>exhaust-gas-temperature sensor sitting between turbo and lambda
>>>sensor. ECU should detect high temperature (not only peak but also
>>>average value) and protect the turbo using the waste gate and/or
>>>switching over to limp program.
>>>
>>>What year of manufacture of the S4 has this exhaust-gas-temperature
>>>sensor?
>>>      
>>>
>
>All biturbo S4's have two EGT sensors, one for each side just inches
>after
>the turbo outlet.
>
>  
>
>>>Is a K04-type turbo charger a solution to cope with the mechanical
>>>and thermal breakdown, independent whether the car is tuned or not?
>>>      
>>>
>
>I honestly don't like the K04's. They're just a K03 housing with a
>different
>turbine wheel. I've compared them side by side now. There are some
>ballbearing alternative turbos going around now that fit our cars which
>are
>a much more appropriate design and are more efficient. If you're going
>through the hassle of replacing the turbos, you might as well go with
>something else.
>
>  
>
>>>To you think the air-mass gauge is a problematic sensor? Do you have
>>>a remedy?
>>>      
>>>
>
>It's problematic more often than not, but you'll get a check engine
>light
>before it becomes a serious issue.
>
>- Keman
>
>  
>
>>>Thanks,
>>>Joe
>>>      
>>>
>
>
>
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>  
>