The output voltage of a coil is determined by the spark plug gap, and the condition of the center electrode. A spark fires better off a square corner than a rounded surface, so keep the electrode filed flat and properly gapped.
A clean plug with the right gap will fire at around 8,000-10,000 volts, and a standard coil will develop 20,000 volts or more on open circuit. If the coil wire will jump a 1/2" gap to ground as the engine is cranked, you've got plenty of voltage to run the engine under any normal operating conditions. High performance- - - -that's a different can of worms. A high-performance coil for street use is an exercise in futility.
Jerry
