Adjusting Boost

[Michael McBroom]

DemonTSi at aol.com wrote:

> Uh oh...does anyone happen to have the URL mentioned? I accidentally deleted
> the original message containing it right after replying to it, but not before
> getting the chance to check it out!  :(   TIA

I knew I should have included it.  Here it is:

http://www.teleport.com/~bertram/volvoapc/

> 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

'87 745T 123k w/APC                 Visit the Volvo Performance Site:
'88 765T 156k                           http://mcbrooms.com/volvo
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Graduate Student, Linguistics                         Author of 
Research Interest: Biological Origins       =McBroom's Camera Bluebook=
of Language                                     http://mcbrooms.com
California State University, Fullerton			
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