The 'copper' seems to always confuse people.......My understanding is that ALL of the major manufacturers use copper. The copper is not exposed directly to engine heat which is why it doesn't melt. It is encased in a steel compound in the centre electrode.
The performance benefit with Plat, Irid comes from being able to run bigger plug gaps because the reduced firing voltage allows this. Common sense should tell you that the bigger the spark, the better......& more chance of complete combustion.
That big cam you fitted & now idles rough. That rough idle is incomplete combustion & the engine misfiring. I wonder if you had a spark 1/2-1" long.....& hotter....what would it do.
