APC MOD r41+ r101 from the right [Archive] - SaabCentral Forums

: APC MOD r41+ r101 from the right

6th July 2002, 12:07 PM
join r41+ r101 from the right and directly adjust boost with P
anyone done this mod?
Im looking for some clarification on how to join them
do I just bridge the right hand side of the resistors with both ends still attatched to the board
remove and solder the right hand side of the resistors together


7th July 2002, 11:09 AM
I've done this modification. It's seems to work perfectly but it's quite difficult to reach a stabile boost. In fact, if P is too high, you will have a peak power (for me around 1.4bar (i can reach 1.5bar)) and the wastegate will open because of knock (go back to 0.9/0.7 and then go to 1.2/1.3 then back to 0.8.....The solution is to set P around 1.1/1.2bar.
I return to classical apc tweak (thanks tweakers)but i just disconnect the rpm signal. The boost is very stabile, peaks at 1.1bar, stay at 1.05bar until 4500rpm then go down to 1bar.
For the clarification, you just have to join the resistors with both end still attached.

About the apc, i notice that since I put an open air kit (i remove the cat too), i can't anymore reach 1.2bar peaks (maybe i will turn again P&F) BUT i can hold the pressure (1bar) until the red rpm zone !!!

9th July 2002, 04:05 PM
This is the passive or BSR mod. Biggest problem is that to achieve decent top end boost the P pot needs to be wound up. This then gives enourmous spikes at the lower end of the rev range. Alanb is running this mod and his car peaks at 27psi but drops down to 17 at the top end.

Disconntecting the rpm signal seems to work differently on different cars, on some boost seems stable as the rpm taper is removed, on others boost isn't much more than basic as the apc never moves into active mode.

The rpm signal is also used as part of the knock sensing circuit so removing can have other adverse effects.

9th July 2002, 05:20 PM
thanks for the info
I was doing the mod on my spare box to try to isolate the cause of my boost problems
I reasoned that joining r41+101 does away with the pressure transducer input so if there was no difference in boost the problem would be either the rpm signal or knock sensor
there was no difference
so I cut the rpm signal (r23)
still no difference
changed the knock sensor today and the boost is back yaaaa hoooo!!!!!!!!!!!!!


9th July 2002, 05:25 PM
all saab freaks are happy for you !

11th February 2003, 11:21 PM
Well..my pressure transducer gave up the ghost tonight, so I did a search and happened upon this post. Connecting R41 and R101 does indeed bypass the pressure sensor circuit on the APC board! I have my pressure transducer disconnected and I get no solenoid chatter. No for a test drive. I'm not sure where a good setting for P is, so will just play around till I find it. Going to start with the stock Red Box setting. Will update after few test drives :)

12th February 2003, 12:12 AM
With P at about 23k ohms, I was getting about 15psi peaks down to 12-13. With P at about 25k ohms I was hitting 17-18psi...then I think I broke something so I quit and went home :p Car runs fine, boosts fine, just making a weird groaning noise when I first start to accelerate...

12th February 2003, 08:30 AM
ok i took r138 and r42 and changed them. if i did this mod would i increase in boost at all or what? i was reading and it from what i can gather it would do me much good.


12th February 2003, 11:03 PM
You could probably get more max boost out of it, but like the others have said, I've noticed that in order to keep my sustained boost up where I want it, I have to set my max boost higher than before. It "spikes" then seems to drop 4-5 psi for me.

Main reason I did it is because my pressure transducer is shot and I don't really want to spend $200 on a new one.