BigBill makes some interesting points about igntions. Which leads me to say this: one can "side gap" his plugs, and/or "wide gap" his plugs.
Opening up the gap from the stock .035" to say, .045" or more, usually takes more voltage capability to effectively jump the gap.
Side gapping a plug and staying at the stock gap setting of .035" shouldn't require any more spark energy, though.
Old original Champion race plugs were manufactured as side gapped, in a special way. For Indy car engines (turbo'd) and for nitro burning drag cars, not only was the plug very cold, the side electrode was a separate round piece that was stuck in through the side of the plug threads (and gapped at .016") through a hole in the metal plug body.
It took a special tool (made by Champion) to adjust the gap on these plugs, though almost no one did that. My buddy used some of these old Champs in his nitro funny car and I opened up the gap to around .030" on them, since I had installed an MSD electronic ignition on his car. (This was in the mid '80's, by the way, and almost nobody ran an electronic ignition then in nitro cars.)
There are other very interesting/strange plug styles, particularly on the older Mazda rotary engines. Aircraft have some different side (also called ground ) electrodes. The old Kawasake tripple 2 strokes, and some outboard marine engines, used a suface gap plug, which had no side electrode at all. The spark jumped right to the plug body ring. Years ago I remember learning of some Stock Eliminator drag guys who cut off the side electrodes of their plugs with nippers! They were able to get away with this because they had low compression engines and aftermarket ignition systems (allowed by the rules).
