Re: KG4 RPM limit of Points? Or different cam lobe profile?

[foot_doctor]

My Mag machine had the ability to test 4 and 2 cylinder magnetos. It was capable of spinning the mag at 10,00 RPM, but none of the mags we used at that time functioned at that speed. The motive power was supplied by a 3/4 hp DC motor and a variable output DC power supply. The energy required to spin the mag was displayed on an ammeter. Some required more energy than others at the same RPM. The High voltage outputs were coupled to a set of spark plugs with .040" gaps that were in a sealed chamber that had a window that allowed the sparks to be observed. The chamber housing the spark plugs had a pressure regulated air supply that was varied between 0 and 130 PSI. The mags that produced the most consistant output at the highest pressure, RPM and lowest motor amperage were the ones we selected for racing. Mercury and Fairbanks Morse 4 cylinder mags create sparks with alternate polarity. Two positive, two negative per revolution. The strongest positive sparks were needed as the negative sparks more easily passed from the heated center spark plug electode in a running engine. The 2 cylinder Phelon mags created negative sparks, and when we reversed the polarity of the aluminum rotor Bendix Scintilla rotors those magnetos actually outperformed the Phelons. They did require .009" point gap as opposed to the suggested .018’". All of my best "A" motors sported Bendix Scintilla mags with the thin and light racing flywheel. R.T.