[Biturbos4] All causes to turbo failures known?

[Keman]

> 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!

What did the big bang sound like?

One of the things we're seeing on the 1.8T's with plugged up oil pump pickup
tubes, is that when the turbos are starved of oil pressure, the bearings
fail in such a way that the turbine vibrates hard enough to shake the
retaining nut right off the wheel. It then bounces around and does it's best
job of bashing in all the fins on the turbo and ruining it. The pickup tubes
clog up from poor maintanence + non synthetic oil + not letting it cool down
= crusty chunks of oil...

Funny thing is, you only hear it as a loud whining sound. No rattling
blender noise I'd expect. It just starts sounding like a police siren. And
it isn't because the nut gets tossed into the intercooler, I've found it
every time just laying there in the turbo.

> 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!

Which side? The hot or cold? If it's the hot, that could indicate high heat
+ overspin = contacting the housing / instant destruction. If it's the cold
side ..... well that just doesn't make any sense.

Can they take out the turbo oil feed line to that turbo and try blowing
through it? See if it's clogged?

> The argument from the garage is quite convincing:
> S4 chipped (tuned) -> higher boost pressure -> higher turbo revolution
> -> higher mechanical stress -> turbo charger breakdown

"turbo charger breakdown" reminds me of the old castrol commercials talking
about "engine oil viscosity breakdown" as you watched the cylinder walls of
the cartoonish engine glow red then sieze up, followed with stumbling...

..in other words, I aint buying it. :P

> But then I am asking you: How can you drive 5 years and more then
> 160.000 km with the same turbo chargers?

I can think of a Saab 9000 with over 200k miles on the stock turbo that I
know of... that's what in kilometers, 300k?

> 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?

The seal will leak when the shaft rips it to pieces if it breaks... I don't
think the seal was what caused the failure here, it was just an innocent
bystander of flying metal debris... :P

> Is this a feasible explanation for the boost control? Can anybody
> verify it?

Boost control is a bit more complicated than you describe. It's a feedback
system employing EGT and boost sensors along with wastegate solenoids that
attempt to deliver 258ft/lbs wherever possible when full throttle is given.
It has a max limit of ~10 psi while trying to obtain this goal ... the ECU
basically trys to provide you with torque, it calculates it.

How it accomplishes this involves variable camshaft timing, variable intake
runner lengths, ignition timing, injector timing, and injector pulsewidth.
We're talking immensely complicated here... and it's why our engines feel
responsive and smooth in almost any condition outside. Those poor dudes who
make chips for our cars have a heck of a lot to play with...

You should get in touch with a good chip maker... GIAC comes to mind. Theyll
be able to answer a lot more questions than I can on K03 tunability.

- Keman

> Thanks,
> Joe