A colder plug simply means that the plug wicks the heat away better from the tip of the plug back through the seat, leaving the tip colder. The colder tip resists preignition and electrode corrosion better. Its better for high rpm, high load conditions like in racing.
You'll never melt a plug from the cap discharge ignition systems, 84stanglx. The cap discharge systems have more energy because of the way they release the spark energy. The energy is a function of several things a few of which are electrode gap, discharge duration, and the dielectric constant of the medium in which you're creating the spark. Cap discharge simply creates more energy under the duration curve by ensuring that the primary voltage is at a full charge instantly. But I digress. When you've seen people melt plugs, its because of lean conditions (more times than not) in the cylinder, not because of their ignition system. The blower and nitrous crowd will tell you what a sin it is to run lean. The N/A crowd doesn't have to worry about this so much, mainly because we only draw in a limited amount of air to begin with. As far as plug gap goes, a stock motor with stock ignition system will tend to pick up a little power by gapping the plugs a little further. Since the plug is gapped out, the spark travels further from anode to electrode and hence presents more spark surface (energy) to the mixture which in turn creates more efficient burning. This is true to an extent, but when you start boosting compression ratios in N/A motors or similarly increasing mixture density like with superchargers, the dielectric constant of the mixture goes up. Essentially this means that it is harder to force the spark to jump from anode to electrode. This is why racers bring the plug gap down. Remember that the density of air is directly dependent on pressure (pv=nRT) and so is the dielectric constant. So a rise in cylinder pressure creates a denser cylinder charge with a higher dielectric constant. All things remaining equal it requires more energy to make the spark jump across the same plug gap in a 12:1 motor than it does an 8:1 motor. If the dielectric constant is too high for the ignition system, the spark may actually seek ground elsewhere than the electrode; somtimes to the side of the plug or down inside the plug. This will definitely cause a mis-fire in the cylinder. The ignition systems we play with in cars is really weak in comparison to other ignition systems. An automotive system has maybe .3 joules of energy per spark (~1amp for 150 microsecond from 12VDC power) where an aircraft igniter has upwards of 18 joules of energy (15 amp for 300 microseconds from 240V 400Hz power). You ought to see an aircraft igniter spark. It'll throw a 2" long spark, completely vaporizing the air around the tip of the igniter.
You may have to play around with some fuel programs to actually figure out where your injectors are reaching 100% duty cycle. Its partially dependent on the BSFC (base specific fuel consumption) you assume for your motor. With my 24# injectors, I figure I was hitting 100% duty cycle (going static) at about 4800rpm when I was making just under 300hp at the wheels. I pretty much proved this to myself when I swapped to 30# injectors & MAF between rounds and went back out to run three tenths quicker and almost 3MPH faster. There are some programs out on the internet that will let you play with injector loadings. Nothing's exact, so you've just got to use them to explore 'what if' scenarios.
Sorry this ran sooooo long.
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Jeff Chambers
T/S #3
11.86 Seconds/113.8 MPH
Chambers Racing Team