MSD stands for multiple spark discharge, they are designed to deliver spark for 20 deg. of crank rotation at any rpm. In the higher rpm ranges there is not enough time for individual sparks, so one continious flow of energy bridges the plug gap, ensuring that the flame front stays lit. A factory system is a one hit wonder, I too think the GM HEI is a good ign. system, but it has it's limits. To begin it's classified as an inductive system, the coil is solely responsible to reach saturation before the collapse of the field to deliver the voltage to the correct plug. As rpm increases the time for full saturation becomes less thus so does output. MSD and alike systems are classified as capacitive discharge systems, they have that box, it stores allot of energy to keep the coil saturated at any rpm so their won't be a voltage drop at the plugs in the higher rpm ranges. I have dynoed engines with both styles of ignition systems and there is always more power made with an MSD system. Remember power is made from one thing, the extraction and management of the fuels energy, if any amount of fuel that is not burned during the combustion process, is lost power at the crank. HEI can produce up to 50,000 volts, but in the higher rpm and load ranges that will drop off fast, as a racer and engine builder for making power, better fuel mileage, easier starting, more stable idle the MSD ignition is superior...