The ultra-wide gaps, either .060" or .080" were only needed for a couple of years right before catalytic converters started being used. The mixtures were so lean from the manufacturers trying to get a 100% burn in the cylinders that it was possible to misfire with a narrow gap simply because there was no gasoline between the plug electrodes, only air. Widening the gap increased the possibility of having some combustible gas in the spark path. Once converters started being used, the fuel system could be richened up a little, and the converter acted like an afterburner. Richer mixtures and narrower gaps came back as soon as catalytic converters came into general use. On a stovebolt, use a .045" gap with an HEI system.
Jerry
