Spark plugs. Why is it so hard?

Yes sir, I read that. And the only thing I read that was performance oriented was that a fine wire plug takes less voltage to ionize the gap. I don’t think anyone here would argue that. I don’t think anyone here would argue that a precious metal center electrode will last longer than a copper electrode plug. I do know that several ignition engineers I’ve spoken with all have a different opinion of how the ionization of the gap occurs. And that’s an issue because depending on which understanding you follow will directly impact the choice of spark plug. Also in the conversation must be the fact that current OE ignition systems are miles ahead of what most here on a forum like this use. These OE ignitions will fire less than optimal chamber conditions (either rich or lean of stoich and even at that it’s only stoich to about 5% rich for best chamber conditions near the plug) much better than say the Chrysler ignition or the many knockoffs of that concept or even the much ballyhooed HEI. In the case of running these less efficient and powerful ignition systems, a precious metal center electrode can cause an undetectable misfire, which in turn causes an O2 sensor to read rich when the engine isn’t really rich at all. In the end when all the chatter has fallen away, it remains if the ignition is up to snuff then the only benefit to a precious metal center wire is its working life span.

Note entirely. Both platinum and iridium deal with heat better. As a result, they can be run 'hotter' without as much concern for preignition. That means the plugs stay cleaner, and they also stay sharper longer - which means better spark for longer, or better spark with a 'hotter' ignition system longer than a copper plug would last. It also means that they deal with non-ideal conditions better since the plugs are better able to fire with increased EGR, sub-optimal AFR, and will put up with abuse for much longer than copper.

My take is this: tune with copper, fine-tune with platinum or iridium after and then enjoy the car. There's no reason to run a tuned-up engine with anything but platinum or iridium, especially with a souped up ignition (MSD, etc). IMO: copper doesn't last, doesn't stay in-tune (no one replaces plugs before fiddling with the carb), and aren't well suited to anything but stock applications. As soon as you have more spark, more cam, more abuse, copper just stops making sense.