hotrod

spark plug gaps are a balancing act between two extremes.

Wide gaps help cold starting, and low speed torque (if you have enough voltage to fire them. This is not a huge effect but helps a little). Wide gaps will fire mixtures that are too lean or too rich to fire with a normal gap.
Wide gaps cause problems at high rpm and high compression ratios/ boost levels. It takes more voltage to fire a wide gap so its harder on ignition coils, and plugs foul easier as the voltage can't build to the necessary levels to fire the gap if they are wet with fuel or oil as most of the charge leaks to ground. Wide gaps can also be "blown out" by high cylinder pressures and combustion chamber turbulence at high rpm. This causes high rpm miss, and the car falls on its face under high load.


Narrow gaps have trouble igniting rich cold mixtures. They are much more resistant to being blown out at high speed /boost. They tend to give low speed miss especially when the engine is cold. It is easier for the spark to jump the gap and due to this the spark can jump at lower voltages and give a "cooler" spark that does not do as good a job starting the fire. Sometimes this can slow the early stages of combustion a bit so the car acts like the ignition timing is retarded slightly.

The cooler spark can cause missfire across the rpm range if its bad enough.

Larry