SV: Adjusting Boost

[Stefan Olsson]

> > So the Saab APC sounds like a very good alternative to most of those
> > overpriced EBCs out there...but does it allow any form of adjustability
as
> > far as raising the boost pressures? And if so, is it easy to do so
(i.e. just
> > turn a knob or push a few buttons like on most EBCs)?
> 
> Not as easy as the other EBCs.  You have to remove the top half of the
> ECU's case (The ECU is a plastic box about 6" x 8" in size, with two
> screws holding the two halves of the case together), which exposes the
> circuit board.  On the board, you should find three adjustment pots,
> usually labeled "K," "F," and "P" (John Bertram, who is also a Saab
> technician, believes that the "K" stands for 'knock', the "F" stands for
> 'frequency', and the "P" stands for 'pressure'.)  According to John, not
> even master Saab technicians know how to adjust the "K" and "F" pots --
> I guess because they don't have the test equipment for it -- so he just
> says to leave 'em alone.  Adjust the "P" pot clockwise to raise the
> boost pressure.  I would recommend trying it in 1/4-turn increments
> until you get it set where you want it.  John has determined that, on
> his APC installation, rotating the "P" pot to its stop results in a
> maximum boost pressure of 16 psi.  I haven't adjusted mine yet, although
> I'm guessing mine is probably set to between 10 and 11 psi.
> 
> There's more to the APC story, though, although I'm less than conversant
> with all the nuances: there are several different types of APC ECUs. 
> John's website gives you specific data as to which car models and year
> models have the best APC systems for our purposes.  Even within these
> models, though, there is some variation.  For example, Saab made the
> standard "black box" APC, but they also made a special, high-performance
> "red box" APC.  Depending on who you talk to, the red box is anywhere
> from not much different to much different.  I managed to find a red box
> model for my car by sheer luck.  So far it doesn't appear to be much
> different, but then I haven't started playing with the boost yet,
> either.
> 
> Now here's the other side of the coin: So far, I know of two complaints
> Saab owners have regarding the APC, one minor, one not so minor.  The
> minor complaint centers on Saab's decision to taper the boost off at
> high revs.  With my cheezy, non-calibrated boost gauge, you can see the
> boost needle back off slightly under full boost at high rpms.  I suspect
> Saab does this to decrease the likelihood of detonation at extremes. 
> And this brings me to the second complaint: many Saab owners allege that
> the APC is =too= sensitive, and is misinterpreting other engine noises
> as pinging.  When the APC detects pinging, it will back off the boost in
> 1.5 psi incrememts, which can put a crimp in your style in a hurry if
> it's misinterpreting what it hears.  In its defense, however, I must say
> that I have not had an occasion yet where it has backed off the boost
> due to pinging, either real or imaginary, and neither, to my knowledge,
> has John.  So, it may be that this symptom is more commonplace with Saab
> engines than with non-Saab ones.  How ironic.
> 
> One of the reasons why I bring this up is because I suspect that there
> are folks on this list who possess the knowhow to crack the mysteries of
> the enigmatic "K" and "F" settings.  It seems likely to me that the "K"
> setting corresponding to a volume sensitivity control, and the "F"
> setting is simply a filter that will tune the APC to a specific
> bandwidth.  But then, I barely know which end of a soldering iron is the
> business end, so don't put too much credence in what I have to say :)
> 
> -- 
> Best,
> 
> Michael McBroom
> 
Hi all

The APC-system is developed in my hometown !
We have worked alot with this APC-system when we have tuned Saabs and
Volvos.
Its very easy if You only whant small changes in engine output.

P stands for Pressure (thats the only pot to adjust if You whant small
changes)

K stands for Knocksensor sensitivity. In the early days we adjusted this
pot clockweise untill we could here the engine pinging and then we retarded
a little bit. (later we used a knocklink to determen if there was som
pinging)

F stands for Fading (a Saab ing. told me this) and this pot regulates how
fast the boost will rise and go down (ithink You can also call it Frequens
because thats what it is controling)

There is always a problem when You whant some high power output from this
systems because the boost will rise very quickly in high gears and then
when You are at peakboost the knocks makes the ignition to retard (if the
ignitionsystem have a knocksensor) rapidly so then You have lost all power
again (boost goes down and ignition retards at the same time)
I remember that we made some modifications in the system and sold it as a
tuningkit for Saabs. I can not tell You every mods (still selling a few)
but the system works better if You shortcut resistor R42.
We are selling the kit with the P-pot installed on the dashboard together
with a chip for the enginemanagement.



Best Regards
Stefan


http://www.algonet.se/~datac/bsr.sportsman/