Originally Posted By: DrRoughneck
Originally Posted By: Olas
The downside is that copper is a more conductive metal than platinum or iridium.
So standard plugs give out a better spark / better combustion?
Not really, the voltage is so high and the current so low in ignition systems that resistivity of the electrode doesn't matter. The plug wire resistance dominates, and that is by design.
Electrical conductivity in metals tends to track with heat conductivity, so copper also conducts heat better than platinum and iridium, but again the plug designers take that into account.
The only "downside" at all is cost per plug.
The only engines that really "need" dual Pt or dual Ir plugs are ones that fire two plugs with one coil (whether in the same cylinder like Gen III Hemis, or in paired cylinders like waste-spark systems. That's because the electrically positive electrode is the one that wears away (metal ions are attracted off it and toward the negative electrode every time it sparks). When one coil fires two plugs, ONE of the plugs has a negatively-charged side electrode, and the other had a positively- charged side electrode. Single Pt or Ir plugs will rapidly lose the side electrode on the ones where the side electrode is positive compared to the center electrode.
