if you change nothing else
the bigger the gap, the higher the voltage needed to jump it, and therefore the shorter the duration.
power is current (the flow) x volts (the push) and you didn't change the coil so the power available to be used as a combination of current and volts is the same.
higher voltage creates high current for a very very short time and a current flow in general across the gap for a shorter time, You would use less of your reserves of power to jump a smaller gap therefore maintaining a spark for longer. but it may not be good enough to light off a highly compressed mixture.
compress more atoms/molecules that are not of uniform size shape or chemistry into the gap between the contacts you massively increase the number of atoms that need to have their electrons ripped off to make a spark in the first place. you need to rip off enough electrons from enough of them on the path between the electrodes so they can cycle across untethered from their home atoms, carrying the spark.. you are making a tiny plasma path...
higher voltages more quickly degrade the silicone core spiral wound wires we all use.....
its a compromise like everything else
Dave
