"The power stroke is 90 (180) degrees. Since MSD ignition pulses can only be produced at a maximum of every 2 - 2.5 ms, the piston will have moved 12 to 15 degrees after the first spark occurs. How much real benefit is there for this late of an additional spark? The obvious lack of benefit becomes more real as the RPMs increase."
I'm slightly familiar with the ignition system used in MB's modular engines. If I remember, each of the twin plugs fires approx. 12 crankshaft degrees apart. In addition, they fire alternately on each power stroke; i.e. a-b, b-a, a-b, b-a, etc.
Coincidently, this 12 deg. difference is the same spread you calculated for the MSD. My guesstimate is for emission purposes.
Most, if not all of these ignition boxes, cease multiple sparking above ~3000 rpm.
Sherwood
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