Hmmm... am I wrong in the understanding that a "hotter" plug is actually longer for more compression, (igniting the mixture sooner) and a "colder" plug shorter? (related to how far into the combustion chamber it protrudes?) That was always my understanding of how that works... but maybe I'm mistaken? IF that is correct, then the next colder OS plug probably protrudes the same amount as the GRP??? Just food for thought.