Chris,
A bigger gap requires more voltage to arc. This increases the load on the rest of the ignition system. stray current losses will increase, insulation may break down faster, etc. As long as there is sufficient voltage and current, the bigger gap will result in a bigger spark and initiate a faster start to the combustion event. The result is a little like advancing the timing but without as much energy lost compressing the combusted gasses. Perhaps a better analogy is the difference between operating on one plug versus two. The spark plug will be a little hotter and could lead to pre ignition/detonation issues. If the gap is too big, the current finds somewhere else to go and the cylinder misfires.
Smaller gap leads to cooler plugs, which could foul. Too small and the spark doesn't consistently ignite the mixture and the cylinder misfires.
Small differences within the specification probably won't make much difference. If the plugs look a little cool, opening the gap to the max may help a bit. As an old hot rodder, I would always open them up to the limit, but errosion will lead to misfiring a little sooner.
Magnetos make increased electrical energy as rpm increases as opposed to electronic/points that make a reasonably uniform output until high rpm where coil saturation starts to mess things up. Consequently, the magneto could be a little more sensitive to large gaps at start up.
Keeping the electrode edges nice and sharp greatly lowers the voltage required to fire the plug. With the old fashioned ones, you could file the center and ground electrodes flat after they had eroded and re gap them. They would work as well as new as long as the insulators were still clean. That is a little difficult on the fine wire types and the side electrode styles.
Rob
I have a question for all the engine experts on the list.
What are the pros and cons to wider vs. smaller gap in our spark plugs. The given range by Champion etc. must balance several parameters. I am trying to get a feel for why one would choose to be on one end of the range over the other. Also. what might be expected outside the specified range, too small or too large.
I am assuming magnetos here. I imagine the answer might change with EI.
thanks,
Chris Zavatson