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Date: Mon, 07 Jan 2008 00:29:54 -0500
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Subject: [LML] One mag, One electronic ignition
From: "bob mackey" <n103md@yahoo.com>
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> I have not done any tests but I believe if One Mag and One Electronic
> Ignition is used you are likely to fail the Mag Coil prematurely (that
would
> reduce the aprox. 400 to 600 hour normal failure of a new Slick to a really
> unacceptable life).  Why??  One of the principal advantages of EI is the
> variable timing advance that improves power and efficiency.  When the EI
> fires a plug before the Mag, the pressure rise from earlier combustion may
> prevent the Mag plug from firing.

As Steve notes, the breakdown voltage of air does increase with pressure.
If that pressure is high enough, the peak voltage at the spark plug might
not be sufficient to initiate an arc, and so the coil will be subjected
to high voltages for longer periods, possibly causing it to fail sooner.
On the other hand, flames are highly ionized and conductive.
If the flame front has reached the second spark plug by the time
its points open, the voltage will hardly rise at all. The current
will flow at just a few volts.

I won't do the math now, but we could calculate how much timing
difference is required to allow the flame front to reach the
second plug before its spark.