[petek]

Any battery will exhibit a voltage drop when a load is placed on the battery. The drop is due to the internal resistance of the battery (with respect to the load). I wouldn't be suprized to see a two volt drop on a lead-acid battery when you place a 300+ Amp load (starter). Even though a lead-acid battery has plates with fairly significant resistance (i.e. lead), due to the surface area of the plates the total internal resistance of a lead-acid car battery is quite low and that's why we can get 300+ Amps from the battery.

I would guess that the efficiency of the MSD ignition may be lower at lower voltages. Continuing to guess; there may be certain functionalities within the MSD unit that would not function at lower voltages. I would be very surprized, however, to learn that the MSD unit would not produce a spark at voltages as low as 10 volts.

If the MSD unit would not function at lower voltages you'd never be able to start your car when the air temperature dropped as the voltage on the car battery also drops with respect to temperature.