Yes, the plug gap controls the firing voltage, along with a few other factors. Normal plug gap for a point type ignition system is around .035". Electronic ignition systems usually have plug gaps anywhere from .045" to as much as .080" in some cases. Engines that run extremely lean mixtures due to emissions requirements have to run very wide plug gaps in the hope that there might be a few molecules of combustible mixture in the gap when the plug fires. Some Cadillac engines that ran .080" gaps in the early 1980s would miss badly with a narrower plug gap! When GM first introduced HEI in the mid-1970s, they had a tester that plugged into a spark plug boot that required at least 25 KV to fire a spark across the gap. It resembled a spark plug with a recessed center electrode and an alligator clip to attach it to a ground.

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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!
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