Contour Enthusiasts Group Archives Forums General General spark plug gap question

General theory question here...

When a car manufacturer recommends a certain gap, is that the optimal gap for the engine or is that initial gap that will produce an optimal gap at the spark plug's half-life?

Put another way: If 0.050 is recommended, and engineers know that the plug will be at ~0.070 at the end of its life, is 0.050 really the optimal gap or are adjusting for wear and the optimal is ~0.060.

This question tends to keep me up at night. lol.


Brian Dors
99 SVT

the cronic is making u think too much

The spec gap is the optimal gap.

Most plug wear does not widen the gap. Rather, it rounds off the edges of the electrodes first and then erodes the gap long after the plug has gone past it's prime.

My personal habit as a tune up tech for many years before going into service management was to gap the plug at the wide end of spec. That usually produced a slightly smoother idle. The wider gap, within reason, provides a hotter spark that is better to ignite lean mixtures.

Thanks Big Jim, gonna do it tonight so i'll stay close to .056 not .05 like i was thinking.

tune-up specs list a range of .052-.056" for plug gap

Yup, what IBUB said. What I've seen as official = .052 to .056.