Why do manufacturers always brag about the open circuit voltage capabilities of their coils? Once a clean, properly gapped spark plug ionizes the gap at around 8K-10K volts, it's impossible for the coil to build up any more voltage- - - - -whether its open-circuit capability is 20KV or 500KV. The current flow across the plug gap remains constant, and the induced voltage in the coil secondary winding CANNOT rise above the point where the spark begins to flow across the gap.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!