[s-cars] Overboost

Mon Mar 31 05:20:35 EST 2003

Rich,

There are 2 types of overboost. One is passing over
the maximal programmed boost value that's in the boost
chip in your 3B S2. Past this point the ECU shuts the
fuel pump, but not due to the fact that you're getting
more boost but because you're getting more mass air
flow than programmed in the fuel/timing chip. So you
can get as much boost as you want, if you don't get
more air flow, you won't make the ECU shut the FPR
(fuel pump relay) off.

The second type of overboost is the one that's in the
UrS4/S6 and the ABY S2s. That one allows the turbo to
give slightly more pressure than usual (1.1 Bar
instead of 0.8) in some very limited conditions (RPM
below 4500 IIRC and quickly flooring the car). The
WGFV has a map (16x10 in the AAN/ABY/ADU and 16x8 in
the 3B/RR ECUs) that controls its duty cycle from 0 to
100%. The WGFV isn't active below 30% of throttle
opening. Putting a stiffer spring in will in most
cases make the ECU shut the fuel pump off in a 3B and
slightly increase the overboost effect on an AAN
engine but with no real HP gains because once the
overboost period is surpassed, the ECU will regulate
boost to the programmed values. In a 3B, there's no
other way to use a stiffer WG spring other than
reprogram the boost chip with lower WGFV values. But
that alone won't bring anything and if you don't add
more boost and reprogram the fuel chip according to
the boost levels you're intending to run, you may run
too lean and burn a hole into a piston.

HTH and don't hesitate to ask other questions, you
should know by now I can answer these questions :-)

Cheers!

Mihnea
--- Richard Tanimura <Richard at Tanimuras.com> wrote:
> 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?
> B
> 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
>
>
> This message is in MIME format. Since your mail
> reader does not understand
> this format, some or all of this message may not be
> legible.
> --
> [ Picked text/plain from multipart/alternative ]
> 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
> > >
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