im done with iridium it doesn't last that long iridum suppose to last at least 50k miles !! my ngk burnt around 20k ! 5 spark plugs burnt supra guys with 600 hp using autolite copper i tried it it works fine if nkt better responsive at highr rpm i will never buy iridium personally i even tried denso TT bad spark plug i will stick with copper this one dirt cheap from rockauto autolite 3924