If anyone has more info, I'd love it. But so far, what we've come up with is that the mazda speed 3 and focus have normal pistons and the fist has a weird diesel looking piston. Which means the normal NGK that is a couple steps colder on those cars, doesn't really work for us as its not designed for our piston type or flame front crap, so... IdK, something.... I have 2 sets of the ngk's that are colder, but I stopped using them after I read about how they were not the correct TYPE for us. I had ( and still have ) too many variables to add spark plugs to my tuning right now.
I want to get a day when I can do a pull. Change to the ngks. Do a pull. Then change back to the stock plugs again, and do a pull, then post the v-dyno's.
But anyone can do that !!! Someone else do some testing besides me !! Lol.