Oh my, oh my! I've forgotten to talk (OK, I'll make it brief) about combustion pressure and how it affects the spark plug opperation.
As the combustion pressure goes up, for whatever reason, the resistence to the spark jumping the gap increases. Even if you have a stock ignition, under easy operating circumstances you shouldn't have too much, if any, trouble with the way your engine runs. But, as soon as you load the motor by going up a hill, or whacking the throttle wide open, or carrying your fat bro-in-law as a passenger, the spark may not jump the gap very well, if at all.
That is to say, during some running periods, your igntion doesn't need to be high output, and it only puts out as much voltage as is needed. But, as the requirements go up, then the ignition needs to be able to follow along. Again, BigBill refers to that above.
As engine rpms increase, so does combustion pressure. As your compression ratio increase, same-same. Advancing the engine spark timing does this, too, as the burning starts sooner - before the piston gets to TDC - and there is more resistence. (This is especially noticeable at low rpms.) Higher engine heat increases combustion pressure, too, as does better sealing piston rings (think gapless style here).
A better igntion system seems to be the last big mod for the Hinkley twin, as all the other areas have been covered (bigger bore; longer stroke; bigger carbs; ported and big valve heads; bigger cams; freer flowing exhausts). Slowly some bits have become available, such as better coils and ignition wires. The black box is the last piece of the puzzle.
Wow. It's 2:30 am, Mountain Standard Time. Time for ol' GrandpaBauer to hit the hay!
