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Discussion Starter · #1 ·
Hi!

Has anyone tried to use a boost controller and trigger the scramble boost setting with the signal of pin 19 of their APC boxes (knock LED)?

I had a boost controller specifically designed for this by a friend of mine so that it fits directly into the APC box (with APC functions retained!) but he does not have the time to finish programming this device at the moment. At least he did not charge anything for his work since he has not managed to finish it, yet.

Now I am considering using some kind of boost controller from Blitz, HKS, Greddy or Apex'i but I would like to have one which is able to reduce the boost when knock is detected. There are some controllers which allow you to increase (or reduce) the boost when you press a button or activate a switch. I would like to activate this function with pin 19 from APC. Has anyone tried this before?

Cheers,

Tadek
 

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boost controller

Has anyone tried to use a boost controller and trigger the scramble boost setting with the signal of pin 19 of their APC boxes (knock LED)?
Could you explain a little more please? I'm currently finishing off my APC mod and would be interested to hear more.

I was going to try using a set of transistors to be able to switch between normal and modded APC settings, after a few hours of messing about on sunday i gave up and used relays instead, only prob is my APC units now the size of a 60's calculator, but i will be able to set F, P , R138, R40 & R42 as i'm using a pot on each.

I've hooked up a Knock detector LED and hopefully will sort out a switch to keep the APC on when braking, I'm getting really bad lag in 1st gear with my FMIC so i need to sort out some kind of launch control, push the boost up more while sitting on the clutch.

Cheers
 

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Discussion Starter · #3 ·
Well, I am rather annoyed with my APC. The problem is, when you want to run boost levels above 1.1 or maybe 1.2 bar, the APC has the tendency to produce some overboosting spikes when boost is build. You might try to solve this by running higher base boost levels but I reached the end of the thread on my wastegate actuator. Now I got a different one from Collins Racing which I have to equip with a bracket, yet.

But another alternative would be to use a different electronic boost controller.
As I mentioned before, I had one designed which fits the original APC box:

www.akakraft.de/bilder/saab/boost_controller.htm

But this one is not working, yet.

I thought about getting another one. There are some electronic valve controllers, which have a scramble boost function. This means, you can adjust a higher (or lower) boost level for a certain amount of time, which you activate by pushing a button or something similar (full throttle switch might be another option). I would like to use this option to reduce the boost once knock is detected. One would have to use pin 19 of the APC as a trigger. Once the pin 19 LED was activated, the boost would be reduced to a desired level via the scramble boost control function. Simple.

I am sure someone has tried this before. All you need is a boost controller which has the scramble boost function and which can be triggered with a separate trigger input.
 

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APC Boost controller

It's similar to my origional idea, i think you could do it with a NPN transistor used as a switch, if it is switched on (think you could control it by connecting to + and knock detector pin so when you get knock the circuit is completed switching the transistor on) it changes the resistance of the max boost pot. Maybe then mess about with some capasitors so that you can time it to increase/decrease resistance for a few seconds. The altenative would be to use a button which does the same thing, guess that would be the manual version.

I'm just refereshing my electronics knowledge at the moment, it's been a few years since i studied it, hopefully in a month or two i'll have the use of transistors figured out.
Sooner or later i'll start work on some Basic Stamp stuff, that's where you can really start to develop high end control systems.

Better idea, just use a relay, connect the control side to the + and the knock detector, when you get knock it earths which would engage the relay, then you need to run a parrallel circuit around (for eg) R42, it's just then a matter of maths to work out the value of the resistor on the parallel circuit.

(R1*R2)/(R1+R2)= R3 so if R42 is 1000 ohm and you want the value to change to say 750 ohm you would need roughly a 3000 ohm resistor on the parallel circuit

(1000*3000)/(1000+3000) = 750

Unfortunately it does'nt work the other way around, 999.9999 is the max resistance you'll get using a parallel circuit with a 1000 ohm resistor.
 

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Have you thought about DI / APC ?

The common mod is DI + APC which is different to DI / APC in that the DI / APC units talk to eachother. Someone has just fitted DI / APC to his 900 and I think this is the first documented install - I think all the other installations were DI + APC where you keep your original c900 APC and just add direct ignition from an early 9000.

If this works the way I'm assuming it does then knock would be avoided through a combination of boost and ignition control - instaed of only opening the wastegate.

Here is the topic discussing the installation:
http://www.uksaabs.co.uk/viewtopic.php?t=1529
 

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Discussion Starter · #6 ·
Yes, i have considered installation of DI/APC. In fact, I have the complete wiring loom with MAP sensor, DI/APC boxes etc. at home.
I do not like this idea too much, though. The advantage of DI+APC in combination with LH2.2 is that it is rather easy to tweak the APC and it is possible to remap the LH2.2 and DI unit using the LH Editor and DI88 Editor from Ragnar Burenius. When you install DI/APC (which is just a single ECU) you are not even able to increase the boost pressure. Okay, there are people out there who can, but I cannot remap the ECUs myself after doing some mods to the car. If I just go ahead and install DI/APC in its original setup, I will probably have less power than before using my own tweaked APC with distributor ignition.
 

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Looks like you've researched that option. If your thinking about buying an aftermarket boost controller maybe you might consider an ECU that will do it all instead? you've only one half the battle (well 1/3 of the battle) if you upgrade boost control only!
 

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Discussion Starter · #8 ·
Yes, one should really go for MS II. Especially as the V3.0 board is available now. But the MS II upgrade is not - at least at the moment.

I think I'll go that way and try to upgrade to Megasquirt and do all the fueling, sparking and boost control with one controller.
 

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OR.. you could install a 100ohm resistor across the power terminals of your Pressure tranducer.. with a dash mountred switch to add or remove the thing from the circuit.. instant 2 level boost capability.. approx $3 in parts.
 

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Discussion Starter · #11 ·
Have tried that. It does not work. Okay, maybe it does, but this mod does exactly the opposite of what I want. In my opinion with this mod the boost is only raised in lower rpm ranges. I installed an adjustable pot across the pressure transducer and it did nothing to increase high rpm boost.
 

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Is there a relationship between boost & rise rate

Does anyone know if boost & rise rate are connected in anyway, i was wondering what it would look like plotted on a graph, would it be linear or exponential, does the rise rate reduce as it nears max boost?

It would be interesting if you could start looking at the relationship between the two, maybe set up the APC to slow the rise rate as boost goes up, i was thinking it would be better to have it rise quickly initially then slow down gradually as it nears it's peak boost.
 

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"i was thinking it would be better to have it rise quickly initially then slow down gradually as it nears it's peak boost." - this is what actualy happens on most if not all 'modded' boxes. Saab engines are designed for midrange power and so nearly the whole set up of the engine from turbo size, valve timming, intake runner length etc is optimised for this end. When you increase the boost via the APC you mainly end up increasing power in this area and do very little for the top end. The 16V engines are better breathing at high RPM but 8v engines have quite a lot of power fall off at high RPM (not due to APC settings). You do not want fast and hard boost rise as it's going to destroy your gearbox in short order - you want to have a nice steady boost rise that keeps increasing the power right up to the redline like a real sports car. For this you need a turbo that produces power further up the rev range and valve timing that shifts power further up the rev range ( at the expense of low down power). You are not going to get this with APC mods alone as you are fighting against the basic setup of the engine - in my experience the stock setup of these boxes is a good compromise and is specificaly designed to create the smoothest and most constant power curve. You have to remember that the turbo charger produces it's power in a limited power/RPM band - the APC flattens it's peak output (which is in the mid range RPM) to create of a flat torque output but it cannot extend it very well. So if you want better power at high RPM - fit a bigger turbo and change the valve timing via a cam change and or fit a better high RPM breathing 16v head.If you want better low down power for off the line speed - fit a smaller turbo like the mitsubishi. One last point - boost as measured by your guage on the dash is not a measure of how much power the engine is producing - it is only a measure of how much air is queing up in your intake waiting to enter the cylinders. A properly setup car can run high power with low (ish) boost as it is able to consume effeceintly all the air it is fed -a poorly setup car will show high boost spikes as the engine cannot breath the air properly it is fed. In conclusion - modding the APC is not going to get the power delivery you are after.
 

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modding APC

I don't think having the rise rate too fast is going to be too much trouble for me due to the increase in volume of my inlet, what evere i do it's always going to take a little longer to charge as it's neary double the volume of a normal inlet.

That's why i want it to rise quickly initially, but i get your point that replacing the turbo for one which spools up quicker would be the best route.
 

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Rate of the turbo boost rise, turbo lag and throttle lag are not the same thing. Classicaly 'turbo lag' is the dead area in the lower RPM before the turbo produces usefull boost - this is essentialy governed by the physical size of the turbo and the trend to smaller turbo's on modern cars has made this a thing of the past. Throttle lag is the time it takes for air to move from the intake to the cylinders and is governed by intake volume, length and restrictions. Boost rate rise can be equal on any turbo once it has reached it's operating range (although the smaller turbo's are slightly faster due to having less rotating mass)With a zero length and volume intake you will still have turbo lag with a bigger turbo and with even the smallest turbo you will still have throttle lag with a large intake length. I always think of turbocharging as like having a dog on an elastic lead pulling you along on a skateboard - the elasticity of the lead is like the intake length, a whippet is like a small turbo which is quick off the mark runs fast but struggles with a heavy load and a big turbo is like a great dane which is slow to get going but once up to speed will pull a big load without much effort.
 

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Discussion Starter · #16 ·
Yes, the Saab engine is designed to produce most torque in midrange rpm. But so is the APC setup. It is true, there is a relatively small turbocharger and no hot valve timing, but the APC boost curve is designed to taper off at higher rpm, too. All I want is to get rid of this taper, which in my opinion is not possible with any APC mod with a really stable boost without overboosting and spiking.
I do not think that the original setup was meant to create a flat torque curve.
Cheers,

Tadek
 

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Well a flat torque curve is what most engine manufacturers strive for as it gives you the best impression of constant power. By limiting the natural spike of the turbo's power curve they created more of a plateau perhaps than a total flat line. Additionaly you have to remember that there are other factors when it comes to reasons for a boost drop at high RPM - the reduced capacity of the APC to filter knock from increased mechanical noise and the reduced efficiency of the APC to react and control boost quick enough at higher engine speeds. A system controlin high boost at high RPM would have to be more sophisticated - a knock sensor on each cylinder with more sophisticated signal analysis and individual ignition timming on each cylinder. From a marketing point of veiw the driver just wants to put his foot down and go and not feel any sudden changes in power - when you start pushing boost at high RPM and doing it safley this is exactly what can happen. On a cold day with good fuel you may well get nice smooth power right to the redline and teh customer would be full of praise for teh cars performance but on a hot day with bad fuel he would be straight back to the dealer complaning about hesitation and not feeling he had the confidence to overtake - a dealer nightmare.
 
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