Re: Safe Boost

[Robert Houk - SMCC Bos Desktop Hardware <rdh@UrQ.East.Sun.COM>]

   It seems to me that I'm going to have a trade off between safety and
   performance.  Is this a correct interpretation?  I'm not looking for 5

To a first order approximation, yes. Increased power translates fairly
directly into increased stress, wear and tear. The "factory" designed
the engine (the whole car "system", clutch, CV joints, etc.) to sup-
port a certain "stress" level for a design life. Increasing the power
output of the engine stresses just about every component of the drive-
train beyond "design limits", reducing the components' lifetime. In
general, Audi's have the reputation of extremely durable drivetrains
with a lot of "overdesign" capable of sustaining a fair amount of
extra stress (aka "power") without catastrophic failure. One of the
nice advantages of not being the first to do something is all the
counterexamples of what not to do...

   besquillion HP out of my meager little 2.2.  I just want to improve
   performance to safely see about 1.6 or 1.7 bar without that annoying
   "yank-the-plug-out" sensation currently in effect.  Am I searching for the
   Holy Grail?  

   The fix Peter Wales outlined seems quite easy to implement.  But others say
   that overboost protection is gone.  I'm not clear if this is sensor
   saturation or A/D saturation or something all together different.  

Both, basically. On the MAC-02 ('83 UrQ), the sensor outputs 5 volts
to the ECU at 2.0Bar (approx) absolute manifold pressure. This is the
highest voltage the ECU's A/D converter can handle, yielding a "pegged"
reading of 0xFF. The pressure transducer however does continue to re-
spond fairly linearly (increased voltage in direct ratio to increasing
manifold pressure) for awhile longer, so the ECU is the limiting case
here. At some point fairly soon thereafter, the pressure transducer
itself will peg, be it at 2.25, 2.50, or 3 Bar (I'm not running *MY*
engine at 2Bar of Boost!), so at some point you hit another limiting
component. For the UrQ, and this probably translates fairly directly
into many of the '80's series cars, a "simple" ROM change enables you
to run several more PSI of boost (up to about 14/15 for the UrQ), but
requires "electrical circuit" mods to go beyond that.

The experience of the qlisters seems to indicate that 18PSI is easily
viable on the Audis in general (I-5 engines, anyways -- we're all
[I am] awaiting the verdict on the A4QT -- new engine, etc and so forth).
Some lunatics, er, intrepid explorers are running well past 20 with
"good results".

Will your engine/drivetrain last 300,000 miles at 24PSI of Boost? Per-
sonally, I doubt it. It is worth it? Well -- heh heh -- could be...

					-RDH