overboost AAN vs. 3B?

Mihnea Cotet mik at info.fundp.ac.be
Wed Apr 2 20:23:32 EST 2003


The overboost function in the AAN chips is an additional line in the boost
map/table, which lets the ECU control boost to the programmed values if the
overboost conditions are met. So basically a 3B can't have the same
function, even with additional programming, because this would require one
to reprogram the "firmware" part of the chip, which is virtually impossible
and I know of no tuner who can add a real overboost function as in the AAN
chips to a 3B boost chip.

However, a slightly similar overboost effect can be achieved by using more
aggressive WGFV duty cycles at WOT, which will allow boost to pass over the
maximum programmed boost pressure for a few seconds before the ECU takes
things back into control. I dunno how this is possible (normally the ECU
controls boost continuously) but with 20% higher WGFV duty cycles at WOT,
one can achieve overboost during initial flooring, then a few seconds later
the ECU takes boost into control and brings it back to the programmed
levels, and I've achieved this in my own car and a few friend's as well
because they wanted it too... and the torque effect is very easily noticeable.

Dahlbaeck's 3.0 Bar upgrade does indeed provide with more boost in the mid
RPM range before tapering boost off at high RPM for the same HP result at
max HP RPM.

I dunno if there are US chip vendors that can provide with software for a
bone stock engine and a 3.0 Bar transducer (and I don't really care either
BTW), but I can. If you get your hands on a say 3.8 Bar transducer (not
that there are such transducers readily available but it's just an
example), I can do a chip for it, with the same boost levels as what you
might expect on a 2.5 Bar or 3.0 transducer or even more, even if it's not
sane for a stock turbo. By the way, in some cases, running a stock engine
with software for an RS2 turbo (and only that) can be dangerous because
some tuners increase the knock limit in the knock sensor maps. I don't know
if anyone does that in the US but I've recently gotten a chipset from
Germany for analysis purposes (the guy could distinctively hear knock at
WOT) and I've found out some people out there raise the advance at which
timing should be retarded when knock is detected (stock is -2.25 to -3
degrees) by a few degrees so the knock-retarding function isn't actually
working anymore...

Hope this helps,


At 12:12 2/04/2003 -0500, auditude at cox.net wrote:
>Maybe a specific question for anyone who may know here.  a.k.a. Mihnea?
>Is the overboost function of an AAN motor, an additional table in the ecu
>that doesn't exist in the 3B?  Or are these just different values in the
>same tables?
>Dahlback offers two mods for stock AAN motors, one that gives
>269hp/304ftlbs and another that uses a 3.0 bar PT 269hp/328ftlbs.
>To me it seems that the higher torque but same HP indicate higher boost
>pressure at less-than-redline rpm levels, tapering off as rpm increases to
>save the turbo.
>Whether that is translatable to the 3B is the question.
>200q20v mailing list
>200q20v at audifans.com

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