[s-cars] Overboost

[Richard Tanimura]

Just so I have this. Overboost is anytime you exceed the boost prescribed in
target/desired map. Yes?

I am trying to imagine the control system. Is the WGFV like the injectors
i.e. running on a 0-100% duty cycle or variable aperature or what? What are
the factors that affect delay in it regulating boost? Just the time
necessary to move a sufficient volume of air?

Is the control map also 16 x 10?

One conrete question: If you change the wastegate spring w/o changing
anything else, why does this mess up the automatic control system?

Sorry for all these question but this is something I know nothing about and
I am delighted to find somebody who does.

Rich

-----Original Message-----
From: s-car-list-admin at audifans.com
[mailto:s-car-list-admin at audifans.com]On Behalf Of Robert Pastore
Sent: den 30 mars 2003 21:55
To: 'Mark Strangways'
Cc: s-car-list at audifans.com
Subject: RE: [s-cars] Overboost


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Mark:
There are two boost maps that interact to create "overboost".
There is the primary boost map that you can think of as the "desired"
maximum boost.  One axis is throttle position (10 steps) and the other
axis is RPM (16 positions). So as Scott J suggests, there are 160
possible data points in the boost profile.

The second map is the "control map"; this is where the ECU activates the
WGFV to control boost.

The interaction between the two might best be described by a few
examples.   Assume you were at a data point where the "desired" boost
map indicated 1.0 bar of boost.  If the "control map" were set low
enough, say at .7 bar, the WGFV would have plenty of time to gradually
bring boost to the "desired" level, and you probably wouldn't see any
overboost.  Set the control map to .95 bar, and the WGFV can control
boost in time, and you see "overboost" until the WGFV can get things
under control.   Developing the interaction of these maps is an art.
Set the control map too low, and the chipset is sluugish.  Set it too
high, and you have uncontrolled boost.  Get it just right, and you get
"overboost" -- which is really nothing more than clever marketing of a
temporarily overwhelmed boost control system.
Bob

-----Original Message-----
From: Mark Strangways [mailto:strangconst at rogers.com]
Sent: Sunday, March 30, 2003 2:01 PM
Cc: s-car-list at audifans.com
Subject: Re: [s-cars] Overboost


Speaking of overboost...
I was wondering if any one out there knows if there is any output from
the
ECU that goes active in overboost only ?
It's likely a slim chance but there seems to be some knowledge of the
ECU
internals on the list.
The idea behind it would be to enable a water injection device during
overboost only.

Just a thought anyways,

Mark
----- Original Message -----
From: "Kirby Smith" <kirby.a.smith at verizon.net>
To: "Eyvind Spangen" <eyvind.spangen at c2i.net>
Cc: <s-car-list at audifans.com>
Sent: Sunday, March 30, 2003 1:41 PM
Subject: Re: [s-cars] Overboost


> Before I shifted boost control to my A'pexi boost controller I used
the
> A'pexi to monitor boost, both for the stock ECU and the replacement
> Hoppen Stage 1 ECU.  Stock could reach 1.1 kg/cm^2 and the Stage 1
could
> reach 1.3 kg/cm^2.  These units of measure are close to but not
exactly
> equivalent to bar, and are overpressures relative to atmospheric
> pressure.  So 2.1 should be your overboost in action.  Whether you get
> overboost is determined by your ECU, which Scott J. asserts operates
> within one of 160 available boost pressure vs. rpm maps selected by
the
> ECU based on various factors.
>
> kirby, 95 S6
>
>
> Eyvind Spangen wrote:
> >
> > A friend of mine just bought a '96 S6. It goes right up to 1.9 on
the
> > dash gauge, but how and when should the overboost kick in? We've
seen
> > 2.1 on the gauge about two times, but don't know if it should be
more
> > often..
> >
> > --
> > MVH
> > Eyvind Spangen
> >
> > _______________________________________________
> > S-CAR-List mailing list
> > S-CAR-List at audifans.com
> > http://www.audifans.com/mailman/listinfo/s-car-list
> _______________________________________________
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