AW: [Biturbos4] All causes to turbo failures known?

desmond auld desauld at
Wed May 12 05:12:14 EDT 2004

I have two good used Ko3 turbos i removed from a car for a Ko4 upgrade if 
anyone is interested.  What are they worth?  There was no problem with the 
car before removal, just the owner wanted RS4 power/turbos.  The car was 
stock before removal.    Drop me a email and i will let you have pics etc if 
you want.  I have both turbos, for this s4 engine.  Thanks, des.

>From: "Josef Hebenstreit" <josef.hebenstreit at>
>To: "'Keman'" <keman at>, <biturbos4 at>
>Subject: AW: [Biturbos4] All causes to turbo failures known?
>Date: Tue, 11 May 2004 23:43:57 +0200
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>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
>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
>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
>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.
>-----Ursprüngliche Nachricht-----
>Von: Keman [mailto:keman at]
>Gesendet: Mittwoch, 5. Mai 2004 02:31
>An: Josef Hebenstreit; biturbos4 at
>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
>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
>there are codes for reaching the adaptive limit rich set and a quick
>at the MAF under heavy throttle shows much less grams/second measured
>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
>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
>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
>turbine wheel. I've compared them side by side now. There are some
>ballbearing alternative turbos going around now that fit our cars which
>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
>before it becomes a serious issue.
>- Keman
> >> Thanks,
> >> Joe
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