I pulled the Iridiums out of my newer stuff and put copper equivalents in after wondering about this stuff my self. My results seem to agree with what others have found on other forums..
They all ran noticeably better, Especially my little turbocharger hooptie.
Copper is a better conductor of electricity AFAIK...
...Interesting...OK, but even the NGK Iridium or Ruthenium plugs are still 98% (or so they say) copper core, while it is ONLY the end of either electrode that uses a different material.
...My conclusion is the Platinum, Double Platinum, Iridium plugs provided progressively longer replacement intervals. Period.
Street car, beater, driver, which is a PIA to change plugs, the longer life stuff is probably the way to go if you don't want to change plugs..
Performance, race, use the copper or a race plug. And figure on replacing it once in a while.
You do bring up an excellent point: the longevity of the plug. I am not surprised at all that OEMs have been pushing this forward...heck, who ever thought that a spark plug replacement would require an intake monifold R&R? Sure...I had to do that on my V6 Mazda6 once, but yeah, only one time, and that was well after the 150K mile marker, and I wouldn't want to do that job again.
