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Discussion Starter #1 (Edited)
High guys... A coincidence made a tweak of an old mod work wonders on our lovely APC's! I have done a bit of testing on my own car, but the mod has now been tested on 4 or 5 cars here in Denmark. Mine is the only one with the old 14-pin grey version of the APC, and it works on this aswell. We have no loss of boost at high rpm's, but a bit more testing is needed before we can call it a complete succes, but it looks promising! Remember, the mod is done at your own risk...
Here's the mod for the newer 25-pin version:
You need:
1000 ohm resistor
50 ohm potentiometer
Here's what you do:
1. Remove R138
2. Lift right leg of R36 (right according to the text that reads R36)
3. Mount one side of a 50 ohm potentiometer to the left side of R101 (ground)
4. Solder the two other legs of the potentiometer (if this has three) together.
5. Mount one side of a 1000 ohm resistor to the right side of R102 (=+7.35volt reference)
6. Solder the three loose ends togehter (R36, 50 ohm potentiometer and 1000 ohm), you might have to solder a wire from R36 to the potentiometer, as there is quite some way from R36 to the potentiometer.
Almost done, bare with me :)


When the mod is done, put the box in the car. Start the car with the box connected. Measure the voltage between the R101-side of the Potentiometer, and on the other side of the potentiometer toward R, adjust the Pot to 0.365 volt! The adjustment can be quite tricky, so go easy on the potentiometer...

As for the T8-mod, you just leave the removal of R138 out, as this is non excisting in the old grey box. The rest of the mod should work on the T8 aswell.


So there you go, go and test it. Untill now, the most impressing result was made on an otherwise standard T16. The car did a 15.01 1/4 mile run on a semi-wet track... The car now holds 1 bar from whenever it hits full boost untill rpm-redline. Unless the car sees knock, it will lower boost...
The APC also has the boost-mod as per www.900aero.com, that is the R40 and R42-mod.
PLEASE return with results so we can further upgrade and refine this mod...
Again, note it is on ones own risk, but it works on several cars in Denmark untill now. I will test more on my own car tomorrow, but today it work pretty good. I have the box modded with a too high R40, so can't get the boost low enough to get free of knock. This is altered now, but it is late, so testing will be done tomorrow. I hope people will test this, as for now, it looks like we have an "mbc with knock protection", which is pretty good :)
Daniel.
 

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very impressive results. I'll pick up the components and try this mod myself shortly.

as for the 50 ohm potentiometer that's needed, what range is it that's needed? 10-50 ohms 50-100 ohms, 50-100K ohms?
 

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"The car did a 15.01 1/4 mile run on a semi-wet track" -I do find this a little hard to believe from only an APC adjustment. 15 sec 1/4 mile times from FWD cars need some serious power and expert launching.
 

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Discussion Starter #4
Delorean, my fault, you need to be able to adjust the pot between zero and 50 Ohm's...

Trackside: We didn't believe it either, but the time will be published on a different site sometime this week, and I will be sure you let you know where it is, so you can see for yourself. Other times recorded by cars with this apc-mod (one with a fuel-chip to go along) was 16.10 seconds, again, FWD c900. The before mentioned 15.01 run was the best recorded saab-time of the day, and the guy didn't come as close again. He launched a 15.74-time aswell, so that was a bit off... I did a few runs in my T8 aswell, 18.0 was my time, but that was in REALLY wet conditions and without this new mod. But hey, why would I lie? I have been on this forum for a very long time, and I have yet to state something that was a lie, what would be the gain for me? Heck, if it was my car, maybe I could understand where you're coming from, but this T16 holds 1 bar to 6000 rpm, no wonder it's fast...
I will return with proff as soon as the times get on the web...
Daniel.
 

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Discussion Starter #5

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Daniel is right! He did that 1/4 mile at 15.02 on a wet road :D

The guy "casper" has done my apc box's aswell! For some months ago now, but I have not driven them yet! I will adjust them sometime next week or so! I am driveing a mbc now!
Next month I will go for the rolling road and get it testet with the new apc and with mbc, to see the diffence!
 

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Hi Daniel! Nice to hear that the mod is good for the steady boost at high rpm :D.
What do i need to buy at the shop? only a 1000 ohm resistor? and a potentiometer from 0/50 ohm?
Does it make a diffrent how to put the resistor in place?
Do i need to messure only the pot or the r101 together whit the pot?

Greetings Bennie!
 

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Discussion Starter #8
Yes, 1000 ohm and 50-ohm pot is all you need. You have to measure on each side of the Pot, so don't include R101 in the measuring... Will take pictures if needed, just have to source a camera...

Daniel.
 

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Hi. I just bought a 1000 ohm resistor and it is a 1/4 watt, is this good??

Should i use the pin 1 from the potentiometer or 2 or 3??

Gr, Bennie
 

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Discussion Starter #10 (Edited)
You solder two of the legs on the potentiometer together, as it is said in the text above. Just make sure you can measure ohm's through the Pot, believe you just have to solder the center and one of the other legs together, so you end up having two legs in all...
If I remeber correctly, 1/4 watt should be ok for the resistor. Can't remember what mine is :roll:
Daniel.
 

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Discussion Starter #12 (Edited)
Please return with results... Unfortunatly, I get knock at 0.65 or 0.70 bar in my T8, so can't push it much further than that, boost-wise, but it holds the boost well... A bit fluctuating while increasing revs (down in boost a bit, then back up, only doing so once), but all in all, higher boost at top rpm. I don't get the initial boost-spike anymore either, which causes a bit slower accelleration at first, but on the up-side, I don't get knock like I did before when the spike came, so no withdrawel of boost because of knock.

Need to do more testing still, but will let the car cool down for today, no need on stressing the old lady too much... I need to adjust P and F some more...
Daniel.
 

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No accusation of dishonesty Saab-Daniel - just find that figure hard to beleive - I will await the proof. If this was just an APC mod on an otherwise standard T16 and it held 1bar to 6krpm I'm not sure it be repeatable too many times before the gearbox blew or a piston got melted - stock fueling just won't support this kind of power and I suspect the APC was ignoring a lot of knock. This mod sounds very dangerous to me unless you have upgrades in fueling , ignition and IC.
 

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Discussion Starter #14
I've tested my car today, and I got knock (have knock-leds), which caused the boost to lower to base-boost RIGHT away, like it always does... And now, I have proof for the times made that day: http://vezzel.dk/pkj/tider/tider.asp
To get all the saab-times, simply sort by clubs on the right, the saab-klub will be found a bit down on that list. After you choose "saab-klubben", click "send forespørgsel" and you will see all the results made by the saab-club that day. The before-mentioned car is a 900T16 driven by Capser Andersen, driver number 708. The 9000 T driven by Søren Bukdal is also completly standard 2.3 turbo automatic with 200 hp. Look at the times, and judge by yourself... And btw, more power at high rpm wont do as much damage to gearbox, as high power at low rpm, we agree on that, don't we trackside? :)
Daniel.
 

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Discussion Starter #15
Hmm, seems as though all the times made in the finals have been let out, so the fastest of casper's runs hasn't been included. He does have one 15.92-run though, but I know almost a second is pretty far from the above mentioned time, although this time did occour in the finals, believe it or not...

Daniel.
 

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the 15.01 run sounds entirely belivable to me, my car ran a 15.6 with the stock intercooler and the 900aero.com apc mod a while back, with the same setup i dynoed at 195hp to the wheels, so presumably with a really good launch (as most of mine were pretty poor) a 15.01 is within reach.

id be curious as to what the trap speed was though, since that gives more of an idication of the power level of the car than the ET.

sounds like an interesting mod, gonna have to try it once megasquirt gets sorted...

Paul
 

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trackside said:
If this was just an APC mod on an otherwise standard T16 and it held 1bar to 6krpm I'm not sure it be repeatable too many times before the gearbox blew or a piston got melted - stock fueling just won't support this kind of power and I suspect the APC was ignoring a lot of knock.
Stock fuelling on a Lucas car seems sufficient for quite a bit of power. My own car is running stock Bosch (though does have slightly raised fuel pressure) and currently is making 240bhp with an AFR of around 11:1, which is still on the rich side, so there is scope to go further.
 

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Discussion Starter #18
The car is equipped with lucas-injection.

Unfortunatly, there weren't any trap-speeds available that day, otherwise yes, it would have been fun...
Daniel.
 

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Yes I agree that high rpm power is relativley benign to gearboxes (the holy grail of power delivery is high rpm boost with no mid range torque spike) - but 1bar at 6krpm requires a lot of fuel. The kind of launch needed to get these times is not at all kind to a 900 gearbox but I'm perhaps being a bit pedantic as any kind of race off the line is not a good idea with a C900. If this mod delivers this kind of instant performance to a stock T16 then we have all been wasting our time with bigger IC's, higher fuel pressure, better exhausts etc - that's why I'm a little sceptical. I'm prepared to eat my words though;oops: :D
 

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Hi!

How important is the precise adjustment of the pot and therefore the reference voltage?
I did this mod some time ago but did not use a 50 Ohm pot but a 40 Ohm resistor as I found this in some description before.
The boost is nice and steady as long as you use your car to accelarate from low rpm with WOT.
For Autobahn driving I found this mod unusable! The max boost in my car is adjusted to roughly 1,0 or 1,1 bar. If I drive on the Autobahn and have let's say 4000 rpm, I have to easy the throttle because of some idiots pulling onto my lane and then I reaply full throttle, I have EXTREME overboosting. Even if you reaply more load very gently, there is severe spiking of the boost. I believe this has something to do with the new mod. Even if I run real low P-pot settings (F-circuit LED not working at all), I get this overboosting behaviour.
The only other thing I changed recently is my custom 70 mm downpipe.
I will have to remove this APC mod, since the car is not safely driveable with it, as knock can occur whenever I reaply more load at higher rpm. Maybe there is some other problem but I do not know what to start with besides the APC mod.
Cheers,

Tadek
 
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