Not sure, i had the impression that as long as the spark plugs are changed regularly it doesnt make much difference with expensive ones, i realised it happend after one of those really hot days last week or so, cars running temp was stable, is it possible for the sparkiz to just let go or fail at certain revs, recently after one of the miss/splutter expirience the car dropped a cylinder sounded like a rexy, check that all coilpack plug ins were in proper contact, no issues there but after i turned the car back on all 6 cylinders were firing.