GM Coil for 305 - 4 pins?...

[Petrovich]

I'm trying to make a wasted spark setup for my bike. So far, I've managed to distribute the crank signal in half (so that half the revolution, one coil can be fired, and the other half, the other coil). Now, my stock coils are about to head south - I get VERY weak spark.
I found a new GM coil for a 305 89 Firebird Formula in my parts stash. IIRC those are only ~20 bucks a pop, vs 60$ for my bike's. However, those aren't the simple 2-terminal coils... They have 4 pins! And that's not even counting the plug lead.
So which pin does the positive line go to, and which pin does the ground go to? What do the other pins do?
Also, does anyone know of any CHEAAAAAP coils in the 20-30$ range that have simple 2-pin input and twin leads, for wasted spark setup?

[PSIG]

Also, does anyone know of any CHEAAAAAP coils in the 20-30$ range that have simple 2-pin input and twin leads, for wasted spark setup?

There are many 2-terminal waste-spark coils as well as single COP style on snowmobiles and this is a good time of year to get them on clearance

As far as the GM coil - looking into the connectors with the HV terminal at 12 o'clock - the lower left pair (internally joined) is for +12V and the lower right pair is for coil control (ground) and tach.

Hope that helps,
David

[Petrovich]

Thanks!
That sure cleared things up a bit.
Don't know if there are any snowmobile supply stores around, but I just remembered that my friend's V6 camaro uses a coil for every 2 cylinders, so I might just raid his place and grab a couple spare coils
I'm still thinking of doing a standard distributor + single GM coil, though... Should be a bit more straightforward, or so I hope.

[Petrovich]

Ok, I got a pair of NOS oem Camaro ignition coils circa '97... And got even more confused. How do you fire these? As far as I could understand, the plugs are "wired in series", so the spark goes from first plug to the block and then back to the second plug.
Now, does this mean I can't ground the block now?... What about inputs, how do I go about these?...
I'm lost.

[Petrovich]

Ok, all my attempts to fire these coils off of a computer power supply (300 watt) failed miserably. It shouldn't draw more than 10 amps on the 12 volt line, should it?... I tried grounding both plugs, wiring them together, and firing +12 and ground through the two coil inputs... No use. Huge spark at inputs, no spark at the actual plug, and then my power supply shuts down if I take too much time.

[TPI 85 Blazer]

Ok, all my attempts to fire these coils off of a computer power supply (300 watt) failed miserably. It shouldn't draw more than 10 amps on the 12 volt line, should it?... I tried grounding both plugs, wiring them together, and firing +12 and ground through the two coil inputs... No use. Huge spark at inputs, no spark at the actual plug, and then my power supply shuts down if I take too much time.

This is way too much dwell time for the coil and may have ruined it. To test this way, first make sure your power supply, coil and spark plugs are all grounded to the same thing (by grounded, I don't mean the (-) input of the coil). Tie the (+) input to 12V and then just quickly tap or brush the (-) input with a connection to ground. The plug bodies should both be grounded. Both plugs should be connected to the coil with spark plug wires and they should both spark.

The high voltage at the output is generated due to a quickly changing voltage on the input. A DC voltage does nothing to create high voltage output. The current in the primary should be varied as quickly as possible. Maintaining a connection through the primary any longer than it takes to create saturation current is just creating excess heat and possibly damaging the coil.