One of the really bad side effects of a wide plug gap is the tendency for that high firing voltage to find its way to ground somewhere other than across the plug gap. If the plug is gapped to need 25K to bridge the gap instead of 12K, what happens when a plug wire gets tired and goes open circuit, or a wire falls off the plug? How about hitting a puddle and getting a little water on the ignition system? That high voltage will jump all over the place instead of bridging the plug gap.
If somebody does something really stupid like converting a stock-appearing distributor to electronic ignition with a high voltage coil, the tendency for stray sparks to find their way somewhere they don't belong is just about a certainty. There's a definite reason the design engineers chose to use a large-diameter distributor cap and 7MM wires when they converted to HEI. That extra space between conductors and better wire insulation is an absolute necessity.
Jerry
