| Excellent questions.
Ionization in distributors generally only occurs with very small caps, and is not a problem with today's distributors designs. For example, MSD's distributors have vanes which prevent ionization due to the fact that they "stir" up the air, so to speak.
Because the spark has to jump from the rotor to terminal within the distributor cap, the voltage build up does cause the gap from the rotor to the terminal to be ionized but only until the point when the voltage because high enough for the spark to jump that gap.
So, yes, ionization is still present even in the most high tech distributors, but it generally isn't an issue except in very high cylinder pressure applications. The vent hole is designed to avert this issue, but it can cause other issues (weather related, water in the distributor, etc.)
This is one of the reason the Modular and LSX engines are distributor-less. Less rotating mass, greater engine control.
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Mechanical Engineer ~ Ford Mustang Obsessed
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