IGNITION AND SPARK PLUGS
'Bout 1980 mutiple spark plugs reared its ugly head again for about the tenth time. So this time I got an air cooled one cylinder motor cycle engine and made a head for it with five spark plug locations and run it with two magnetos, each firing one or two plugs at once. I found that one plug in right location did just as good as four at once. But I found in artificially aspirated engines with high boost and high rpm (firing), mutiple spark plugs reduce misfires percentage and simply stated makes a little more power with increased durability, but for a Winston Cup engine, once you get in right place, one plug will get it done just fine.
I spent a lot of time experimenting with various types of electrodes on spark plugs, spark plug gaps, diameter of center wire, center wire radiuses, center wire flat multi-ground electrodes, surface gap. flame ignition or plasma ignition. Various ceramics qualities in regard to dialectric strength, heat range, center wire sealing and the battle to remove all moisture in the center wire seal area. Remember I worked as a consultant twice for Champion spark plug. Matter of fact the first complete Champion plug lab with dyno was at my place 'bout in 1957 time frame and came back as a consultant again in the early '90s. So you could say I am half way qualified to talk spark plugs.
I found small diameter center wire and a glass seal the best. The ceramic material formula and heat treat are very crucial to dialectric strength. Sharp edge flat center electrodes are the best, rounded electrode is very negative. More gap, say like .075 is best, but takes a very good ceramic with a no moisture center wire seal and a strong ignition in amperage and duration. This then puts plug wires in trouble reference leaking. As a rule no plug wire can handle it as good as a wire with added protection from a premium wire shield like Moroso blue. Seems like mutiple ground electrodes are a little better, less misfire, especially late in race when oil control weakens. (This is not a power tool for round track racers.) This was durability medicine. I found we as a rule used too cold a plug.
I think ceramic should be 'bout 1100°F for best ignition, the heat reduces the chance for misfire because of oiling or incorrect air fuel ratio. Plug gap should be all the sytem can stand reliably. I believe in individual coils for each cylinder with no plug wires. Here's a five cent tip on coil or condenser reliability: if either one gets so hot it burns when you touch them that engine will soon quit making noise. Remember it's harder to transmit electrical energy in elevated temperature without a significant loss of voltage also.
Comparing a three foot plug wire to a one foot plug wire, about half the voltage is lost. Now this information is nowhere's near as critical to normal surface transportation engines as in state of the art racing engines. With a coil per cylinder we run without plug wires so I did the best I could. I plugged into spark plug surrounded with a heavy silicon boot for mechanical and dialectric strength and a sleeve which increased the dialectric strength of the wire. When we had to run plug wires.
How 'bout platinum or other precious or exotic metals for spark plug electrodes? My experience is these expensive metals add life and durability, but for say a 500 mile Indy race they wouldn't be any advantage at all because all the race plugs are replaced every race. Where mutiple electrodes are part of the design only one pair of electrodes will react, that being the pair (current and ground) that offer the least resistance, so mutiple electrodes offer one advantage, optional electrical path in case of fouling of the normal or primary pair.
The spark plug is now damn near 100 years old, and essentially the same since day one.
Flame or plasma will react a much greater range of non-stochiometric cylinder charges.
Only predecessor a spark plug has would be striking a pair of flint stones, or rubbing sticks together.
