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Discussion Starter · #1 ·
Hi guys,

I just picked up my '89 900 T16 yesterday and I realy like it. One thing I have noticed is the lack of quick spool up and lack of boost period. The stock turbo gauge will peak 3/4 in the yellow and never reaches anywhere near the red. I also don't feel the cick back once the turbo spools up like I have felt in other T16's. Would this be a wastegate adjustment? I will be adding my MBC to it soon so would this solve my low boost issues?

Also, since there is an APC and all sorts of complicated vacuum controls for the turbo, where would I add the MBC?

Any comments appreciated!
 

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the APC system is a very well designed system which will help to protect your engine from damage occuring due to knowcking, pinging, low octane/quality fuel, etc etc. i would recommend looking at upgrading the fuel chip and APC and doing other things to the car before switching to an MBC system.
 

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Discussion Starter · #3 ·
So, adding an MBC would damage the engine (or in other words not be good for the engine) unless I do APC mods? Is it because the APC will not be compatible with the MBC?
 

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I'll give this a go, someone please come in and correct me if I get it wrong.

As I understand it there is no need to add an MBC to the older APC saabs as you can achieve more boost by adjusting/ modifying the APC circuit.

When I got my T16 it was boosting to just below the red section and spool up was pretty slow. I have since adjusted the pots inside the APC and spool up is a bit quicker (though spool up time is largely dependent on RPM, thus dropping down a gear will give much faster spool up), and maximum boost is higher.

you can change some of the resistors inside the APC to allow for more max boost, but in the end I left it as it was and simply asjusted the two pots. I put the F pot to maximum (it was close to max anyway), but adjusting the P pot made the most difference. I did overdo it a bit and it was boosting to about 1.2 bar but it kept hitting the overboost (same as hitting the rev-limiter - sudden loss of power, not nice) and I don't want to put that much strain on the engine.

I have backed it off a bit and it now boosts to 1.0 bar and holds pretty well (with good fuel) and occasionally goes to 1.1. (stock for a T16 is 0.75 or 0.85 for a Carlsson "red box" APC).

if your engine can handle it you can change some of the resistors in the APC and change the overboost threshold to get much more boost.

So as far as I can tell an MBC is not necessary with APC (except where the APC is software based, in which case adjustment is harder).

if I got anything wrong please someone correct me.....

arum
 

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Discussion Starter · #6 ·
Ok, Last night, I added the MBC temporarely just to see how it would react.... I also added my boost gauge so I can see more precisely what is going on. Here are my observations.

With the stock APC it was peaking at just about 9 PSI. After I added the MBC and turned it up a notch, I managed to get it to boost to 16-17 PSI and everything seemed to work well. Again, I was not able to get rid of the slow spool up. When I got home, the check engine light came on for a bit then came off. I don't know if I did any dammage but everything ran just as fine as before.

I read up on the APC and I think I will go that route. I'll simply max the 2 pots as you said and it should match what I did with the MBC.

Hopefuly after I swap the intake manifold from the 2.1L, spool-up should be a bit better.

The slight dissapointing thing about this is that I noticed that my previous c900 that I converted from N/A to Turbo seemed to have more power. During the first 2 months of the conversion, It was pumping at 13-14 PSI and gave me a huge ammount of power and allot quicker spool up. (and this is in an N/A car) Could this be because it has greater displacement (2100 cc's as opposed to 2000cc's)

Any ways, I have all sorts of other niggles to work out first. I have to swap the exhaust from my other car because this one is falling appart, I have a weird Idle problem wich I think could be the AIC valve, the clutch master is completely shot and makes me sqweal the tires every time...

Main things to do are exhaust and clutch master.

Oh and all the locks are broken with one key broken into the trunk lock.... car starts with a screw driver..... I have to change all the lock cylinters for the ones in my other car.....

all in all, I have tons of spare parts and the tools to do all of this, just not that much time

but ya, I'll max the 2 pots and that should do it..... I also think the I/C might be full of oil as there was some in the intake pipe...
 

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don't simply max out the two pots, you have to experiment to get the settings right.

with standard APC circuit (ie no resistors swapped) you can max the F pot (max boost) but will have to find a balance for the P pot (rising rate, or something like that) DON'T TOUCH THE K POT.

Get a multimeter and measure resistance for the p pot before you move it for referance. mine was about 9 ohms (or Kohms or something) and is now about 24, once you get it near to 20 you will have to change the scale on the multi meter or it will show a dodgy (.08 or something) reading. Basically if the P pot is low boost will take longer and won't go so high, but if you simply max it out it will overshoot the max boot, hit the overboost switch (causing sudden loss of power - it cuts the fuel like the rev limiter - and can be very dangerous mid-overtake) and then bounce up and down like a horny dog on speed.

it's all about balance with the P pot. If you get it stable with P but can't get enough boost (wish we had petrol even 2x what you pay for it!!) you will have to mod the APC circuit.

that's about all the advice I can give at this point as I have not been further myself, except that I cleaned out the intercooler the other day and now it holds boost for less time and the boost is not so stable. I will have to turn P down a tad.

for more info on APC modding join the forums at 900aero.com and/or check out their tech info pages.
 

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Discussion Starter · #8 ·
Ok, so I took out the APC and did a test run with the F pot full clockwise and the P pot 1/4 clockwise and nothing changed. Brought the APC back to the table and maxed the P pot. There was maybe .5 PSI difference after maxing both pots.

I then added my cone filter and shortly after that, discovered 2 vacuum leaks. After fixing those, went for a test run and max boost went from 9.5 PSI to just a bit over 12..


Even after doing both those test runs I could still hear a hissing noise coming from the driver's side fender. This leads me to believe that there still is another vacuum leak. Furhtermore, I will also check the wastegate actuator adjustment to see if the rod is adjusted longer than it should be.
 

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Discussion Starter · #9 ·
Does anyone know what the black plastic oval box is that sits right above the charcoal cannister in a c900T? It has about 5 vacuum lines running off of it and mine has missing connections...... could be causes of weird boost?
 

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Discussion Starter · #11 ·
That seems to be it.... I found it in the Bentley manual. I also found the source of the low boost. It's the brake switch on the pedal. I read that if the brake switch for the lights is pressed, the boost is defaulted to base boost. I had noticed 2 days ago that my rear lights would stay on...... I think the sensor under the brake pedal needs to be adjusted because I pull the pedal and click, the lights go off.
 

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bingo, I found something similar for the clutch pedal and my Cruise control, I tend to leave my foot resting on the clutch (just a tiny amount) and that was enough to activate the pedal sensor, I thought the CC had stopped working. I Was wrong.
 

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Discussion Starter · #13 ·
thank you so much for all the great info and help so far Arumdevil

Ok, so I did tune the APC as you suggested with the P pot tuned and the F pot maxed. (I revised it tonight) I also tried part of the mod listed in the 900 aero website but did not have a 1300 ohm resistor for R40. I didn't have the 2 resistors they were asking for, so I only replaced R42 with a plain wire (ommiting all other steps) but that gave me barely any boost so I guess I'll have to try that one another day with the proper hardware. After re-tuning with standard R42 and P pot 4/5 to the max, boost rises not too fast but lets me enjoy a fiew seconds with 15 PSI of boost before it quickly jolts back to 9-10 PSI. I presume this is either because of knock or maybe just either the boost cut-off or fuel cut off...... don't know but it doesnt feel like fuel cut off because the engine does not choke like on a speed governor.

Las question: My 2.1L N/A conversion'd car would demonstrate almost neck-snaping acceleration with 10-13 PSI, why does the same ammount of boost give me less of a " jolt " in this car? could the 0.1 of a litre in engine size realy make that much a difference? Alos, my understanding was that an APC'd car would have much greater tuning pottential than my N/A but so far does not seem that way... can someone please explain this to me?
 

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Boost is only one part of a complex equation. The amount of ignition advance that is being applied is another.
I ran my 9k Aero with a MBC for three years until I repaired my ECU to allow me to run the engine with APC. Even though I'm running slightly less boost, the engine feels far stronger at all speeds and throttle positions. I believe T5 can detect that the APC is not in control (no voltage coming in to the ECU from the APC solenoid) and adjusts the ignition advance to protect the engine.
Nick.
 

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I tried the same thing with the hard-wired mod- didn't have a 1300 ohm resistor but I removed the other one and replaced with a wire. I have since fitted a spare APC box with all the standard circuitry and just tweaked the pots. the wire in place of the resistor didn't seem to make any difference on it's own.

AS for the boost on your car dropping back, that sounds like knock to me (or intercooler soak? I'm still looking for a larger front mount intercooler). Using a higher RON fuel will help if you can source some. Hitting the overboost switch is very violent - same as hitting the rev limiter - if this was happening you would know about it and advice would be to lower the boost 'till it stops as it can be very dangerous mid-overtake!

Also you might consider installing a knock LED. it's quite simple to do (I fitted mine the other day) and you will get a good idea of how much knock you are (not!) getting. I had a LED in one of the switch houses on the dash (originally for the alarm system which hasn't worked for 15 years), I simply took out the left speaker on the dash and fed the wire from the LED through the hole under there into the engine compartment. I then soldered another wire onto the appropriate pins inside the APC, drilled a hole for it, and connected the two next to the main fuse box. I've only seen the LED light up a couple of times on one run (running about 1.0-1.1 bar) so at least I know it works, but knock doesn't seem to be much of an issue
 

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Discussion Starter · #16 ·
I think you are right with the I/C soak or something..... I will take it out this afternoon as I finish work early. I bet I will find tons of oil in it .... I will either clean it or exchange it for the other one I have.... Now the other day I was thinking about fitting a second I/C..... would this be good?

I could either find a way to install the 9000 I/C or just get extra piping and install my other c900 blackstone intercooler in series with the other one.... I presume spool up would be a bit slower... what if I hooked up both I/C's but in paralel instead? wouldn't that double my flow and increase cooling?
 

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not sure TBH, but someone else might have something to add about that. if you have two intercoolers try the other before you clean the current one out. I cleaned mine out the other day (there was a LOT of black [expletive deleted] in there) and since heat-soak seems to be worse!!

even so, had some fun outboosting some cool-fool in his 9-3 vert on the motorway today, and having no trouble keeping up with a 2003 scooby, (E reg= 17 years old!), (that is, no trouble except for all those bloody middle/outside lane hogs who wouldn't let me past )

may the boost be with you
 

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Discussion Starter · #18 ·
[ QUOTE ]
may the boost be with you

[/ QUOTE ]

Yep, and with you as well.

Let's hope the "Knock" moster doesn't steal it!
 
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