[BiturboS4] Turbo failure modes

[Philip Pace]

Awwwww man... per your last paragraph, I didn't know about them still spinning
fast as the RPMs go north. My problem is that I try to build _no_ boost before
I hit 175 (the second tick). I set my own max RPM at around 3500.

Your explanation is excellent, Dave. Thanks for the input and I'll throw this
at my girlfriend and see what she has to say about it NOW.
philpace

--- "Edwards, Dave" <Dave_Edwards at iOra.com> wrote:
> Phil,
>
> I'm no expert, but I do talk to experts whenever I get the opportunity.
All
> have told me so far that the warm-up is more important than the cool-down.
>
> I think you're right that turbo failure is most likely to actually occur
> when the turbo is hot, especially when it's spinning fast. But wear is
most
> likely to occur when its cold, because the oil is not lubricating
properly.
> As long as the turbine is not spinning much that's OK. However spinning
the
> turbine fast whilst the oil is not lubricating properly is bad news.
>
> AFAIK there are the following main failure modes:
> 1) Turbine 'seizes' up. Mainly due to lack of oil, probably from coking.
> Reason is use of semi-synth or mineral oil, and/or not cooling down
> properly.
> 2) Turbine bearing wear. Mainly due to improper lubrication. Reason as
> above, but also due to not warming up properly.
> 3) Turbine blade stretch. Due to overspin. Reason chipping to far too high
> boost (for given air flow).
>
> The main point is that turbos often fail for a combination of reasons, not
> just one. If you want your turbos to live long then you need to address
all
> the causes.
>
> Regarding the 2500, yes I did not make myself clear. What I meant was that
I
> keep the boost AND the engine revs low. Yes I do have a boost gauge, but I
> don't need it during warm-up: As you know, trying to drive the car at for
> example no more than 0.5 bar boost is not easy as once the turbos are
> producing such a boost, it's too easy to go higher. No, much better to
just
> be gentle on the gas and you know that there's probably no boost at all
> without even looking at the gauge.
>
> However my main point about the 2500 rpm is that if you gently accelerate
> the car but don't change gear, you can get the revs well above 2500
without
> registering much if any boost. As a result you might think that you're
being
> easy on the turbos, but you're not: The rate at which the turbos spin is
> related to engine revs. They are still forcing air into the intercoolers,
> however most of it is being recirculated by the DVs. Yes they are under
less
> stress because of the recirculation (lower pressure differential), but
> nevertheless spinning the turbines fast whilst the oil is cold is still
not
> advisable.
>
> As I said, I'm no expert and am ready to be corrected if I'm wrong.
>
> Cheers,
> Dave
>
> --__--__--
>
> Message: 15
> From: Philip Pace <pjpace at yahoo.com>
>
> I agree, but was told recently that the warm up doesn't matter that much.
H=
> ow many turbo failures happen during the winter months in cold areas?
> Warming = up the oil takes forever under those circumstances. If there IS
> stress on the turbos when they're cold, wouldn't you think that more would
> fail when it's cold out? All I could say was that cold causes them to
wear,
> but heat ultimately destroys them. She didn't buy that. Can you address
> this?
>
> Also, you say that you keep the RPMs below 2500? That's when you're likely
=
> to get the most boost! Do you have a boost gage? I was surprised at where
> and = how boost is on the car. Maybe you already know. I've been leaving
it
> in a lower gear longer and overall boost is a lot lower during warm up
time.
> My 2¢
>      -Phil

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