Adjusting Boost

[Michael McBroom]

DemonTSi at aol.com wrote:

> Like I mentioned in another post regarding my messup  :)  I was informed that
> the Saab system manipulated the pop off valve...which is not a very good way
> of controlling boost. If it does use a solenoid to control the amount of air
> that goes to the wastegate...then it is basically an electronic boost
> controller a la HKS EVC, Greddy Profec, Blitz Twin-SBC, etc...only it is OEM!

Yup!  (Please ignore the email I just sent off to you.  It was pointing
out what you've just said!)

> Hmmm...so is the APC ECU a separate unit from the car's ECU?

Yes!  This is one of the things that's really cool about the Saab APC. 
It is a modular, stand-alone system.  I have installed it on my '87
Volvo 740 and it works very well.  I noticed Stefan Olsson posted John
Bertram's Volvo APC Project URL info earlier.  I used the very well
documented information at John's site to do the conversion.  I don't see
why it couldn't be adopted to any turbocharged car that uses a
pressure-driven wastegate actuator, although it might be easier to
implement on some cars than on others -- mostly because of the knock
sensor.  

The APC requires a 12-volt source to operate (I ran a fused wire from
the + side of the coil), rpm info from the - side of the coil, a place
to tee in the pressure transducer (I used the line running to my boost
gauge), and a knock sensor.  The APC transducer is tied into the engine
air supply at three separate points (turbo compressor, waste gate, and
air intake).  The pressure transducer acts as a cushion to smooth out
boost onset by supplying pressure information back to the APC, in a
feedback loop of sorts.  The knock sensor is the Bosch type that is
secured with a bolt through it's center, and is identical to the one
already on my car.  The nice thing about this arrangement is I was able
to piggyback the new knock sensor on top of the old one.  Can a
different type of knock sensor be used, like a GM for example?  I don't
know, but I suspect it can.

-- 
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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