Like 94GrandPrixSE said, it's about the waste-spark engine, not whether or not there's boost. Platinum gets brittle and breaks because it can't handle the abuse. Copper's soft enough not to break off in the engine, but doesn't last very long. Iridium does a great job.with boost it is said they do not like the platinum plugs. and i know that even NA they don't like double platinum.
stock. and go back to the stock coilpack. I also am assuming your joking on the 140* thermostat. Your car would act retarded.I was wondering what the best plug I should get and your opinions. its a 97 gtp, cold air intake, 140 degree t-stat (was in it when i bought it) slp cat back, msd coil packs and wires.