I wonder what the physics behind that could be . . . .Could the platinums be a little hotter than they should be? there is very little difference between platinum and irridium, both are related, and both are dense, hi-temp, and corrosion resistant. Irridum is a little better that platinum, but copper is nowhere near either. Must be something to do with plug design methinks. I was going to go with Autolite AP606's but maybe I'll just do plain 606.