[s-cars] Re: Normal turbo whine or is it a leak?

[henryb at tsainc.com]

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Aaron,

Regarding your second point about the puff/puff sound when you let off the
gas (after accelerating with boost)... this is the sound that the stock
waste-gate makes under these conditions.  If you have been to see any of
the racing quattro's -- they make a similar sound only more of a screech
as they change gears, the street S-cars are much more subtle.

Now with regard to your questions on the turbo spool-up sounds and why it
doesn't always pull as hard  other times.  The over-boost mode on these
cars require a number of conditions to exist for over-boost to happen.  If
for example, if the coolant temperature is not hot enough (approx 75c),
then you won't get any over-boost.  As well, there are a number of other
factors that effect the boost.  If you have not read sjm's pages on the
"ABC's of Turbo Boost", you should check it out, it has alot of excellent
and detailed information (sjmautotechnik.com).

Now your point about the surging during over-boost acceleration... I too,
have experienced that sensation on my '92 urS4... and I don't know what
causes that, although it is very minor.  Maybe some other listers will
have more insight on that condition?

Brent

Original message:

Message: 5
Date: Thu, 01 Aug 2002 10:40:29 -0600
From: Aaron <aaront at cox-internet.com>
To: Audi - Scars <s-car-list at audifans.com>
Subject: [s-cars] Normal turbo whine or is it a leak?

Hi listers,
Ive been wondering if my car has some sort of boost leak but im not
sure.  As I have never driven another S its hard to know what it is
supposed to sound and feel like.
It seems sometimes the car does not pull as hard as at other times and
may occasionally surge a bit under full pedal.  Other times it pulls
like a sled dog but smoother.  It is a stock 95 avant with no boost gauge.
If I nail it at around 3000 rpm I can hear the turbo begin to whine and
im sure this is normal.
Now if I apply some brake while keeping on the gas during this spool -
up at say 3800, this whine will increase to quite a scream even though
rpms do not increase. Is this the turbo continuing to spool up inspite
of the rpms not increasing or is this some sort of boost leak? ( Don't
worry - this is not commonly practiced)

How can the turbo continue to spool up with out increase in engine rpm?

Now another curious noise - not likely related - :
If I let off at say 4500 and slow down with compression I can hear a
slight sort of "burble" or puff/puff sound.  Im quite certain this is
not a back fire type noise as it is very subtle.  It seems do diminish
or go away when car is fully warmed up.
Mabe small exaust leak?
Should I rig up a boost gauge for test purposes?

I really wish I could make it to one of the "events" to compare notes
but until then Ill have to get by asking these silly questions.
None of my local mechanics have a clue about the ins and outs of these
cars.
Thanks
Aaron