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Discussion Starter · #1 ·
Here is a list of modifications that you can do yourself on your C900 T16 or 9000 Turbo (pre DI) APC unit.
I have had a lot of people asking how to mod their APC, and here one that I have tried.

R = Resistor, D = Diode, C = Capacitor and Pot = Potentiometer (variable resistor)

Replace R42 with a 500ohm resistor and connect R41 and R101 together from the "right side", when viewing text right way on PCB. This cuts out the 'F' Pot, making boost adjustable with just 'P' Pot. Eliminates boost taper, allowing full boost to redline.
(Here is where I replaced 'P' Pot with two wires, drilled a hole in the APC box, and then soldered a 50Kohm Pot to then end, and mounted on the dash, allowing base boost (.6 Bar) to 1.6 Bar adjustable on the go... just make sure the Pot is LINIER!, a Logarithmic Pot is unusable!)

MODIFY the Ignition Retard stop on the distributor, as this will allow higher boost levels before detonation. You need to pull out the advance/retard arm from the distributor and modify either the stop that is attached to the advance/retard capsule, or the arm itself... just shave 2-3mm from either, to allow the ignition to be retarded more under boost. (Or buy a unit from a red box as standard car)


Another modification I found somewhere, but have no idea what it does is this -
Remove R104
Remove C28
Remove R40, and replace it with 1k ohm Resistor
Remove C25
Remove C26
Remove D36
Remove the wire patch between R103 and R51
Remove C31

If someone wants to do this one, then I would like to know what it does compared to stock. The site I saw it on said nothing of results of modification.

I hope that this will help people get more
from their pre-DI Saabs and cost them less than a Red Box APC unit. Also I find it more fun if you do the mods yourself, rather than buying an off the shelf unit.
 

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So, when you do these mods you don`t need any chip because these does the same thing? I`m going to do the mods on the APC as described on the 900aero-site in the near future, got a 87 mod 9000T. Only changed to openair-filter and tweaked the F and P on the APC, yet.
 

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Discussion Starter · #4 ·
unless you run extremely high boost, you don't need a chip, as the AMM will take care of the rest of it. I was running 18 psi on my '87 9000 T with some of the mods described above. I modified the ignition retard stop to retard the ignition to around 8° BTDC at 1 bar. standard is around 10-11° i think (been a while). if you run more boost than 18psi, i think it would be adviseable to raise fuel pressure a bit, possibly go either a 3.0bar FPR or a RRFPR that is adjustable.
trust me though, that much boost is dangerous on the standard suspesion.. way too much wheelspin!

BTW - i recommend doing the link between the two resistors to remove the boost taper, as when you tweak F and P, you need to find a balance, otherwise you will get surging (as the boost rise rate "P" is too high for the boost limit "F", so it will overshoot, then drop down, then so forth)
AND make sure you modify the ignition retard stop if you run high boost, but dont retard the spark too much, as you will end up losing power.
 

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I already got a 3 bar FPR innstalled, just have to get me a bar/PSI-instrument so I can see how many PSI I now actually have, the goal is 18 PSI, or else I have to change a couple par things to add more boost too, and that have to wait anyway. Just got to do these mods fast as possible.
 

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Discussion Starter · #6 ·
I know that people are running over 20psi on the stock ECU, just adjusting the injectors or FPR instead. I was running at 18psi with very slight pre-ignition (40°C + days) with stock IC, injectors, fpr.. infact the only mod the car had was my APC mods...
 

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Then I have done the mods on the 900aero.com site, the mod with 0.9 bar to 1.5 bar (13-22PSI):
copy-paste from the site:

Locate the R42 resistor
Exchange the resistor for a wire.
<Option: exchange the R138 to 40 kohm resistor, not really needed. More info further down the page>
Locate the R40 resistor (909 ohm).
Exchange the resistor for a 1300 ohm resistor.
Don't touch anything else.

but I didn`t see the big difference from before when I just turned the pots on the P and F without mods. Will see in the weekend, will get a turbo boost meter then, and get at 17.5 PSI (don`t want to go much further, must change the dump-valve at over 19 PSI). Only reference from before is just to see how much over the redline the boost goes.
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

The difference with changing the components rather than just tweaking the pots is that the response curve changes. For example, the boost taper with RPM can be adjusted to hold the boost higher up the RPM range, giving more power without necessarily any increase in boost.
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

Hi there.

I stead of starting a new thread I might as well pick up this one.

It seems that there is a lot of interest in tweaking the APC box on pre DI saabs.

I have got a 1988 9000T with Kat( 160bhp) it is modified with the original saab "redbox" to get it back the non-kat's 175 bHp.
However, what is 175bHp nowaday? So I have decided to go for the mod descibed on www.900aero.com.
Especially changing the boost tapping seems appealing.
Before I start changing/trimming pot( F & P) values, I just want to hear you guys about the difficulty trimming these things?
I understand that the F-pot( max boost) is not too sensitive, but that .5mm on the p-pot can mean the difference between fantastic and undrivable?
Anybody, got some tried and tested pot settings?

Now to another question.
As my car is with the Kat, I wondered if it works( more power) to just swap the kat with a piece of pipe? ( and then just refit the Kat again for the anual MOT)
Have anybody tried this?

I am looking forward to hear your replies.
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

I have a 87Mod, and it comes default without cat. But however the one that was fitted when I bought it was full of rust, so now I got another newer exhaust with the cat removed and a pipe is fitted instead of it. That exhaust stood on a 9000 2.3T (200HP), and it ran much better with the pipe instead of the cat on it, came past the annual control without any cat too.
And I saw a nice difference when I adjusted the P and F some more after I modded the APC, the P was too low so it just ran out of boost early on the RPMs but now the boost keeps good until the RPM limiter. :p
Now my engine looks a little bit [expletive deleted] up (and I who as driven as softly and slow the last week), and suddenly some noises came from the engine. It may be one of the cylinders that`s [expletive deleted] from before, some scratches on it and it looks like it`s blown some valves before (and that`s what happened again I think from the noise). The car will just relax until I got time to see on it, and I might got some help with it too.
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

So you recon it will work removing the kat?
I mean your 87 did not have a kat standard as mine. I mean is it as easy as just to remove the Kat( what about the info the lamda gives the engine)?

Are you also saying that tweeking the APC will damage the engine? or is it just you giving your car hell?

I am going to Le mans together with a mate in his Peugeot 406 3.0 V6, and the mission is to leave him in the dust all the way through germany.
At the moment I cant take him, but I guess a few mods will do the trick
 

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Discussion Starter · #12 ·
Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

When i modded my APC, i did the mod to remove any function of the F pot. this makes adjusting the boost very smooth and predictable. I highly recommend doing this mod.
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

It`s just me who is giving my 400 km 9k 87-mod hell I think.
One og my cylinders didn`t look fine when I changed the engines top-gasket(?) either, some months ago. It`s then I saw the scar on the cylinder.
The exhaust worked fine with the 92-mod 9k 2.3T after removing the cat from the exhaust too, it ran much faster and came cross the annual testing without any cat (luck?). Might help a half sec or so from 0-60MPH. If the cat is a little bit damaged from before, there`s no use in it after all. What you also could do, is to use a hard device (example a bat) and remove/destroy all of the cat from the inside so you don`t have to change the pipe every annual test. And then refit it, with the "cat".
 

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Discussion Starter · #14 ·
Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

I had an '87 with cat, and was running fine at 330k kms wit hthe mods i did to the apc/ignition.. an estimate was around the 190-200bhp mark after the mods, which made the acceleration quite respectable... i also had the mod done that flashed an LED when the APC detected knock, just to let me know how hard i was pushing it (and to let me know if it was anything else that was reducing boost apart from knock.. like a bad APC connection)
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

Well. I will start modifying my APC next week.
I will do it in steps.

I have decided to start with only changing R42( wire/ 0 ohm resistor) and R138(40k), this I understand should reduce the boost taper and give more top end power?

The next mod should then be to alter max boost and the boost rise!
I would really like the boost to pick up a bit faster, at the moment it is like a spounge at low revs

I have not decided if I will do the mod descibed on 900aero or if I am doing Grentarcs mod.
I like the idea of only one pot and boost adjustment on the fly. However, I can not find this mod described anywhere with evidence to back it up?
Have you got a link?

The 900aero mod is well descibed and documented, but I am a bit worried to mess it up since the P-pot apparantly is extremly sensitive.
I cant find any pot settings anywhere
Has nobody had a multimeter across the pots after finalised trimming?

Last thing will be to remove the Kat. But again, is it that straight forward? I mean the difference between a Kat version and a non-kat version is not just the Kat, but also a lambda sensor etc!
 

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Discussion Starter · #16 ·
Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

The pot on the dash, you need to remove the F pot (wire link across two resistors) for it to work properly. As for documented, the site i got it from is no longer up, but i did it to my own car and it was great.. wet days, reduce boost so it is more drivable.

The reason i started this thread ages ago was because the site i got my mods from (and then i kept going past their documented ones) was no longer available, so I thought i should get this up for everyone, as i had trouble adjusting F and P together.. i prefer removing F so its just adjustable by P
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

Cool

I will get back when I have done the mod.

Cant wait to eat the Frog( Peugeot 406 3.0 V6)

Cheers.
 

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Discussion Starter · #18 ·
Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

When i said 'remove F pot" i actually mean, bypass the circuit for the F pot. then you need to remove the P pot from the PCB, and run 2 wires (the conductors from Cat 5e cable works well.. preferably stranded too, for flexability) out to a pot and make sure that it is wired so the resistance of the pot increases as you turn it clockwise, otherwise, as you turn the knob down (anti clockwise) the boost limit will rise....
Good luck with it!
 

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Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

Hi there.

I have now done the mod described on 900aero.
replaced R42 with wire
changed R138 to 40K
Changed R40 to 1K3

Is it better?

Hmm well, it boosts harder but it is not quite right yet.
I am running standard octan 95
in 3rd 4th and 5th it boosts into the red, then drops down into yellow and then comes up again and so forth.

Is this because it detects knock( could try octane 98), or because I need to trim f and p( hav'nt touched these yet)

The car is driveable, but so far it does not seem that much quicker( if at all).

P and F pot values anyone?
The nice thing about changing R40 to 1K3( maybe I should try a lower value, perhaps 1K1?) is that the pot is not touched and hence it is realy easy to get back to the original value.
Is there any resistors around the P pot that can be changed instead of trimmig the pot it self?
 

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Discussion Starter · #20 ·
Re: T16 Saab (C900 and Pre-DI 9000 Turbo's) APC m

also make sure you modify the ignition retard stop on the advance/retard capsule. What you need to do, is grind/file down the top of the stop, and adjust the timing, so that when the capsule is pressurised (use air compressor at 20psi), it brings ignition timing down to 8°BTDC. then you release pressure from capsule, the iming should be around 16°BTDC. If the timing is more advanced than that, it will give better off boost performance, but as long as the full pressure timing is at 8° BTDC, you shouldnt have too many problems with knock.
On my '87 9000, i took about 1.5mm off the stop, and it retarded the timing to 9° BTDC with a static timing of 16° BTDC.
You cant really incease boost without either modifying the ignition retard stop, or replacing the whole capsule and arm asembily with one from a car that came with a red box ecu as standard.
hope it helps!
 
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