Senior Tech Team
Join Date: Apr 2005
Location: Fountain Hills, AZ
Re: Gapping spark plugs....will a smaller gap mean better gas mileage?
The main criteria for plug gap is the type of ignitition, fuel mixture, and intended use. Stock points ignitions may not fire gaps over .035 reliably (and max gap decreases with rpm). Electronic ignitions are capable of firing much wider gaps but most performance engines won't see any benefit (power or mileage) from gaps beyond about .045. I've seen factory HEI applications that called for .070 gaps but they were because of extremely lean mixtures in smog engines. The larger the gap, the more spark energy it takes to cross it. That extra energy results in a bigger spark which is helpful when mixtures are very lean (and also if they're really rich) but if the extra energy isn't available, there's no spark and it's a miss instead.