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I have just stumbled across a complete Edelbrock Vara-Jection model 9356 kit for practically free. It's an older electronically controlled system that uses vacuum/boost and engine RPM via the coil. Because the kit was designed for older vintage USA cars I'n not too sure about the coil connection. Picture a 70's vintage Corvette for example. The instructions say to connect to the negative of the ignition coil primary. The question is my Turbo Legacy probably uses a voltage signal that may be entirely different and with electronics involved that could be bad. Anybody up on ignition systems old and new? This system can be jumpered for 4, 6 and 8 cylinders luckily for me, so I'm thinking I can use it ok with a bit of help from all you folks out there in Legacy land.
thanks!

Hmmm. Well, I guess some experimenting is required. I've measured the dc volts at each of the 3 wires on the ignition primary and it's 12vdc at each. Unfortunately, my meter doesn't have the frequency feature on it but there is of course an AC component proportional to the firing of certain cylinders. Question. How come 3 wires and why not four? or five with a common for all the four windings? I wonder if they fire two plugs at the same time and one wire is common. One cylinder firing at the beginning of the power stroke and another at the beginning of the intake stroke? Anybody know how this might work? If this is the case maybe I could attach the this wire from the WI controller via a small circuit that would add the two pulse trains together.

If I remember right both coils get a constant 12 volts, then they are gounded as needed to fire the spark plug. I think you should find a different way to drive the water injection.

It only has three wires because cylinder 1-2 share the same coil, they fire at the same time. When cylinder one is on compression cylinder 2 is on exhaust, so firing the spark will do nothing (or at least remove any remaining fuel).

Makes sense alright. The only other option might be to use a tach signal but it would have to be amplified to near 12vdc I suspect. I thought maybe on using a couple of diodes off of the two wires feeding the primary windings capturing the positive pulses, but I guess it will still be only half the number of pulses I need.
Time to hit the books I guess. Thanks for the reply Ciper.

I believe ciper has it nearly right -- the only thing is that the ECU grounds its end of the coil winding normally and then releases the ground to create the spark.

It sounds like this thing was designed before the advent of distributorless ignition systems. You may or may not be able to use one of the two low-voltage lines going into the coil pack. I believe you can use either of the outside pins on the 3-pin coil pack connector (the middle one is +12v, and the other two are the low voltage negatives). To confirm it, you can just check that it doesn't have 12 volts on it when the ignition switch is on but the coil pack is disconnected (and obviously the car's not running).

The signal ought to be workable, I'd think... it only handles two cylinders' sparks but it sparks twice for each cylinder per camshaft revolution, so it should still look similar to a distributor-ignition 4-cylinder engine's signal from the negative terminal of the coil.

Thanks vrg3. I'll check those wires out tomorrow and let you guys know how things went. What did you think about using the diodes off the two wires going to the primary of the coils ie. anode of one diode to primary of one wire and another diode anode connected to the other wire. Then solder the two cathodes together and off to my control unit. Wouldn't this reflect the 4 cylinders as in the days of distributors. I think that I'm going to have to really experiment (with the nozzles facing my windshield) before I finally give in and start spraying into my throttle body. It does make life interesting though. Thanks again!

I'm not sure that kind of diode arrangement would work. The negative terminals of the primary windings are grounded whenever they're not firing, so you'd never get a signal to your control unit. What you might do is connect the cathodes to the coil wires and the anodes together to the control unit. You may need a pull-down resistor to ground, too, though... and that would mean you're messing with the primary circuit more than you probably should. A higher input impedance conditioner circuit would be better.

But, like I said above, I don't think it's necessary. Our cars' waste spark setup sparks each cylinder once per crankshaft revolution anyway. If you combined both ignition channels' signals together I think you'd have to switch the control unit to 8-cylinder mode.

Oh wait, I had my "cathode" and "anode" backwards in my head...

I agree with what you said about the diodes then. The issue of the control unit's input being floating when the engine isn't sparking is still there, though, since the input would be either +12v or floating, and never ground.

"sparks twice for each cylinder per camshaft revolution"

Thats not right, remember its a Boxer engine, explained something like "two boxers punching in unison." The two pistons opposite each other are synchronized, the valves are what is reversed. If it was a four channel system the 1st cylinder would fire once for every two revolutions. Since they are shared it fires once per revolution.

What ends up happening (relative to cylinder one) is that the 1st coil fires every time the piston reaches the upper limit of travel and the 2nd coil fires when it hits the lower limit of travel.

ciper, I said "camshaft revolution," not "crankshaft revolution."

A four-channel system would spark each cylinder once per camshaft revolution (just before the power stroke), or once for every two crankshaft revolutions. Our 2-channel waste-spark system sparks each cylinder twice every camshaft revolution, or once every crankshaft revolution (every time the piston nears top dead center, as you say).

A distributor also would have four channels of ignition, sparking each cylinder for its power stroke. There would be a spark every 90 camshaft degrees, so ...

Oops.

Sorry, Gordo! I got it wrong! You'd only get half the number of spark signals since you'd get sparks every 180 camshaft degrees. You really do need to combine the two channels for your control unit, unless you can put it in 2-cylinder mode.

Thats right. CAMshaft revolution has two sparks.

Hey, what an interesting topic. I brought this up at work to all the car buffs and they were really scratching their heads! Great fun. Ok, seems we are getting some place here though. No, there isn't a two cylinder setting on the controller We'll be using 4. I checked out the wires going to the coil pack and it's the outside wire as you had suggested. It would be nice to scope them, but I don't have that luxury item at home. I tried passing water through the nozzles over the weekend using the windshield washer and it's not exactly atomized; it's more like a squirt gun. Scares the heck out of me thinking of putting all that into the cylinders. I'll be doing some bench testing first for sure. I gave my Dad 2 signal generators years ago. I think I'll ask for one back. The pump is a variable speed DC motor which gives me a sigh of relief, as this means that the volume of water is controlled in this way. How else I suppose. Lastly, the one big item which will present a problem is where in the heck can I mount a plastic gallon tank under this hood? I have more stuff under this hood than you can imagine. I've already ripped out the A/C. I was thinking of under the battery bulk head with an extension neck or something. Thanks for all the great feedback lads!

Thats not right, remember its a Boxer engine, explained something like "two boxers punching in unison." The two pistons opposite each other are synchronized, the valves are what is reversed. If it was a four channel system the 1st cylinder would fire once for every two revolutions. Since they are shared it fires once per revolution.

What ends up happening (relative to cylinder one) is that the 1st coil fires every time the piston reaches the upper limit of travel and the 2nd coil fires when it hits the lower limit of travel.

Does this contribute to the great torque that we get in any way?

-Ryan

you could always pin into the back of the #1 injector ground or positive depending on if the system is polarity sensitive, as this is an rpm dependent signal to fire the injectors which indicates rpm just as well as the spark, the vara computer probably takes this signal to adjust pump output so rpm signal is all thats relevent, i believe the vara system delivers a variable volume of water/ methynol depending on its rpm input and cut in/ out setting, so you dont flood, id set it towards mid range rpms, im a vw guy w/coil packs so this is what id do,

it will work like high grade fuel and will require more timming to increase milage/ performance unless you already ping due to high compression or turbo

if you guys have distributors , buy an adjustable timming light or borrow one from your friends and try to advance as much as you can before and anffter the system is armed w/ your choice of octane, depending on octane you will still need to adjust the vara jection and distributor timming to actually increase performance, you could run as if you had like 110 octane if you have an ignition advance option. ive read alot about h20 injection, im gonna buy one of these kits off of ebay for my gti 1.8t and let you guys know what i find. once again timming advance while running the system is necessary, w/ a 1 gallon jug you should get quite a few miles before you run out, so keep an eye on it so you dont have to keep ajdusting timming. good luck