[Biturbos4] Unholy smoke (no more!)

[Chris Newbold]

On Tue, August 9, 2005 11:00 am, Keman said:

> The big thing I'd stress here is that the turbos in stock form aren't
> unreliable, especially when you take precautions like letting them warm up
> and cool down.

That was my own personal opinion too, until I got my car back Friday
night. Here's the poop:

Once the old turbos were off, the tech inspected them and found that there
was excessive play in the bearings. So I was pretty close to a "big bang"
turbo blow-out, if I had ignored the cold-start smoke much longer.

The tech seems to have done an excellent job: everything looks just right
under the hood, there are no strange noises, vibrations, etc. when under
way. No more smoke on cold start, either. Other than a slight "new
something" smell immediately after shutdown, you'd never know.

My respect for this guy has gone up a few notches.

Given that I've done everything "right" from the day the car left the
dealer's lot (warm-up; cool-down; synthetic oil, changed every 5k; no
chip; the car is an 01.5 with the larger oil returns; new BPVs every
year...) and the turbos were toast at 55k, I've adjusted my thinking.

I think the bearings in these KO3s are marginal at best. I don't know if
it's the heat, the airflow (i.e. RPMs), oiling or what. But the bearings
wear more quickly than they should. Then you get a little play. Just a
teeny bit. At first, maybe nothing noticable. Maybe just a little blue
smoke.

Then the play gets just a little worse. Maybe there is enough leakage that
there is insufficient pressure to keep the shaft floating and then *BOOM!*
Lots of smoke and a grenaded turbo. Or, maybe the play was bad enough that
a blade nicked the housing, then *BOOM!* Lots of smoke and a grenaded
turbo.

Obviously chipping only exacerbates this problem, since all stresses are
intensified. No wonder more chipped cars blow up. I think it all comes
down to how hard and long you lean on the boost.

On a car like this, I should be able to drive the wheels off (_not_
abusing it) and it should go over 100k without major incident. The fact
that driving it the way it "should be" driven results in such premature
failure of the turbo bearings is a major issue. Just look at the early
'90s S4 (the "original" S4). People regularly chip those beasts way over
300HP and the stock turbo just snickers and asks for more. Damn near
bullet proof, those were.

What I cannot explain is why the single KO3 in the 1.8T motors doesn't
suffer the same fate on a regular basis. The 1.8T is more than 1/2 the
displacement of the biturbo 2.7T, so the single turbo should be seeing
more airflow than each in the 2.7T. The 1.8T is also a tuner favorite. I'm
thinking maybe heat: the turbo in the 1.8T has a much more friendly
mounting than the two in the 2.7T...

-Chris
2001.5 S4 Avant 6spd (w/ shiny new turbos)