Unlike battery-powered ignition systems, magneto-generated spark actually gets hotter as the speed increases. In the pre-electronic ignition days, Vertex made a line of race mags that were about the best thing going for all-out performance use. They also didn't quit working in case of a battery failure.
The downside- - - -it was usually necessary to push-start the engine, or have a battery-powered backup system, as at normal cranking speeds a magneto produced a very weak spark, or none at all. Commercial magnetos such as those used on farm tractors had an "impulse coupling" that wound up a spring and snapped the mag around at much higher than cranking speed for starting. Race mags didn't have that feature.
Jerry
