The type of coil, either E-coil or can coil does not determine if a resistor is used. (there are other laminations other than E as well) It's the resistance of the coil that's critical and the control of the coil determines if a resistor is needed. When points control the coil in most to all cases a ballast resistor is needed. The coil is actually rated at a lower voltage for starting.
Electronic, MSD (and other CD), capacitive discharge is very short, it can only fire 1 to 3 times but spark duration is in microseconds. Therefore a resistor is not needed.
Electronic, Variable dwell, Ford & GM, inductive discharge, current is limited by the coil driver electronic device, either by varying length of time, or learned then stored in memory (GM). Any kind of coil has a time constant or a rate of current increase, this can be used to limit the current by stopping the current increase at a point in time. Therefore a resistor is not needed.
Electronic, PE (Pantera Electronics), Coil current is not dwell dependent, it is a proprietary design and a resistor is not needed.
The maximum spark time length is several milliseconds, over 100 times the spark length of CD.
Just passing this along. Hope it helps.
