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To understand what's going on, you need to understand the dynamics of wastespark ignition...
Most people understand the part about a dual tower coil firing into two "chambers" at the same time, but it's what's happening on the spark plug end that makes it interesting.
A spark plug firing into a compressed chamber requires more power to overcome the (spark plugs) gap - as compared to firing at "0 atmosphere" or outside of the engine.
Add fuel into the whole mixture (no pun intended), and it gets even harder to fire.
A spark plug firing into a chamber that has already ignited is surrounded by ionized gases and particulates (combustion by-products) that helps the arc jump the gap.
Add to the fact that the later scenario is usually at the tail end of the combustion cycle (and starting into the exhaust cycle) which means that pressure in the (compressed) chamber is starting to drop at this point.
Less pressure = easier for the spark plug to fire
Now, let's look at the wastespark, dual tower coil...
It's just a step-up transformer with the two tower (outputs) coupled.
Fire voltage through the low side, and it gets stepped up by the coil depending on the ratio of the windings.
Now, the coil can fire either:
1) tower 1
2) tower 2
3) both towers
Most of the time, it does fire through both.
When it doesn't have enough power, it tends to fire only one side.
Now, remember earlier about the imbalance of the chambers?
Guess which side it's going to fire if it had to pick?
Due to this phenomenon, this is why the coil drops one side occassionally.
rising chamber pressure + fuel = increase resistance to spark plug arcing the gap
dropping chamber pressure + burnt gases = decrease resistance to spark plug arcing the gap
This is why a totally stock ignition FC will sound like this when idling...
brrrrrrrrrrrrrrrrrrrrrrrr, brr, brrrrrrrrrrrrrrrrrrrrrrr, brr, brrrrrrrrrrrrrrrrrrrrrr
Even with the car in top shape and running perfectly, the wastespark is still dropping a spark every so often.
That small hiccup is an ignition misfire.
Partially to blame is the inadequate electrical charging system in the FC.
The stock FC alternator SUCKS.
At idle, the alternator is barely producing enough voltage to charge the battery.
Once the RPM's climb, this isn't much of an issue, so you don't get misfires above idle speeds.
We fix it by installing CDI boxes which totally cures this "problem".
I run a Crane Cams HI-6 myself.
I usually install CDI boxes in all my customer's cars.
-Ted
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