Ok, it's time for spark plug theory 101. In designing a spark plug, the very most critical aspect that the engineers have to consider is controlling the temperature of the center electrode tip (heat range). Too cold; and it won't burn off the deposits, which leads to fouling, Too hot and it will cause pre-ignition. Since engine operating conditions vary widely, heat range requirements also vary by a considerable amount. Platinum plugs had their first significant usage during WW2 in British aircraft engines. The primary advantage of a platinum plug is that it extends (widens) the EFFECTIVE heat range of the plug. It has the ability to act like a colder plug at high speeds, and a hotter plug at low speeds. Remember the critical design features of keeping the deposits burned off while not causing pre-ignition? That plus the increased erosion resistance makes the platinum quite attractive for some applications, especially now with unleaded fuel and modern, clean running EFI systems. Platinum has the ability to utilize a small electrode without deforming under intense heat and pressure, thereby it can run hotter at low speeds to keep the deposits burned off, yet it resists the tendancy to cause pre-ignition under heavy loads. I dunno just why it can do that, you'll have to ask someone smarter than I, but it does work that way. The notion that a platinum plug tip is smaller so it has a more concentrated spark is pure nonsense. The actual size (diameter) of a spark is miniscule, the visible portion of a spark is from the aurora of the ionized particles in the actual current path of the spark, sorta like the glow of a light bulb, only shorter duration. The spark occurs at varying places around the electrode, just pull the plug on your lawn mower, ground it, and pull the starter rope. You can see it quite readily jumping around all over the place. I have no idea why a platinum plug won't work just fine on MSD systems, sounds like more nonsense to me. All that an MSD does is trigger successive sparks. Big deal. One thing that often happens when changing from standard plugs to another type is the EFFECTIVE timing may be altered, requiring a slightly different initial ignition timing. This is not because the spark is faster/slower (pretty much impossible) but because the fire gets lit more (or less) efficiently and the flame propogates differently through the chamber. Remember, all you are doing with a spark plug is lighting a fire. Very quickly. Over and over. As long as you can do that without fouling the plug or causing pre-ignition, it matters not one whit if you use platinum, copper core, resistor, non-resistor, whatever. They all have certain characteristics that make them desireable under different conditions, but don't lose sight of the primary mission of the spark plug. They really are one of the minor marvels of modern engineering.
Joe
