The MSD just fires one coil at a time, however one coil fires two plugs at the same time, witch plugs it fires are determined by where the plug wire goes, the factory had them fire plugs on oposite sides of the engine for emmisions but with a coil desighned to fire both in one cyliner at the same time you can do it that way or you can get plug wires to make the "take off" coils fire both polugs in one cylinder.