Pretty sure the Plat/Irid plugs also use copper, but not 100% sure. But it makes no measurable difference to the overall resistance in the spark plug circuit: The 'copper' is in the form of a slug encased inside a steel/nickel core of the centre electrode, about 0.5" long. What do you think the difference is in micro ohms between a piece of steel & copper, both 0.5" long? Then you ADD to the circuit because THESE resistances that are in series & become additive before a spark can be generated: rotor button resistance, rotor air gap, coil sec resistance, spark plug gap, spark plug lead resistance. Millions of ohms. Much ado about nothing.....
What I said about Irid/Plat plugs in post #15 about the extra benefits is 10000% correct.
From the Bosch Automotive handbook 9th edition, 1500 + pages.
" '[ leaning of the mixture ] is accompanied by an increase in the energy demand needed to ignite the mixture. By enlarging the electrode gap, it is possible to increase the volume ignited by the spark & thereby raise the energy content. However, enlarging the electrode gap requires an increase in ign voltage......The electrode gap should be......as large as possible so that the ign spark activates a large volume element & thus results in reliable ign of the A/F mixture by developing a table flame core."
Plat/Irid plugs allow larger gaps with the same ign system, reducing the chances of misfire & increasing the chances of complete combustion.
