Quote:
Originally Posted by john_cramer
Sal, I've written a lot here about dwell, search under my name for some history. I am working on reverse engineering the old tach circuits for fun and to understand the input signal it's necessary to translate the dwell into a duty cycle.
The reason the automotive world went away from CDI is because even though the charge time is short, the spark duration is also short. Klaus Lattinger (klatinn, inventor of the LM-1) developed a system that would use a capacitor to start the arc then switch to a transformer for a very hot, long burn. This eats the plugs in half the time but a set of plugs is only about $10 for a 911. Anyway, if you have a clean sheet of paper, that is the road I would follow.
Search here and on the Innovate forum for more information.
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John,
MSD ignitions say they gaurantee spark for 20deg of crank rotation, that's a lot of spark duration. Below 3000RPMs they generate multiple sparks, as many as needed to fill the 20deg slot. Then above 3000 there better units claim to control the amout of time the single spark lasts. Maybe they have come up with new tricks here. I plan to get my hands on one of there controllers, right now I'm looking for a used MSD DIS-4 unit, this is top of the line 4 CDIs in one unit. I can first use it as single CDI with stock distributor and see how that works. Then I can goto Wasted spark and use 3 of the internal CDIs and simply never use the 4th. The box is designed for 8cyl cars, then they also have a DIS-2 for 4cyl but nothing for 6cyl.
I'm just wondering how much a CDI system such as this might help the 3.2L. Some have said don't bother and leave well enough alone. But I'm always tinkering.
As for Dwell: if you use the MSD products they don't care about the stock dwell, all they care about is a negitive (ground) going pulse 12->0 volts then they simply only look at the positive (rising edge) 0->12v edge, it's this edge that's important this is when in the stock config the Ground is removed from the coil '-' and this in turn causes the spark. So the MSD products simply look for this transition 0-12V and this tells the CDI to fire. They claim it all happens so fast that it does not introduce any timing retard at all. We shall see.
Thanks for the dwell tips.