[Fwd: Re: overboost AAN vs. 3B?]

auditude at cox.net auditude at cox.net
Wed Apr 2 16:13:58 EST 2003

Hi Mihnea,

Thanks, this is good stuff.

Honestly, I don't even know what those conditions are that allow an AAN to have overboost.  I assume it has something to do with initial takeoff or throttle change/position or something.

But now that I think about it some more, perhaps it doesn't matter if there is an overboost function or not.  What if I simply want to push, using your example of IA's 3.0 bar PT-using chip, 1.65 bar at midrange rpms, and whatever is normal for high rpm?  There's no overboost function required to do that, is there?

So, let's say I get a (Bosch) 3.0 bar pressure transducer, and have you setup a chip that uses that PT and a stock engine/turbo, with the exception that it runs a bit higher boost were it can, like the Dahlback chip.

This is only something I'd want to do if it was safe for the engine and turbo to do so.  Later, I would get a different turbo and some other stuff that would put the higher pressure transducer to more use.

Possible?  Desirable?



Mihnea Cotet <mik at info.fundp.ac.be> wrote:
> Ken,
> 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,
> Mihnea
> At 12:12 2/04/2003 -0500, auditude at cox.net wrote:
> >Hello,
> >
> >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.
> >
> >Thanks,
> >
> >Ken

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