pfr6g / bkr6eix i've used without fail in both my tuned v7's and no issues with misfire, until recently with my car. but, they were new plugs, so i knew that wasn't the issue. new coils on, misfire on boost gone. have heard coppers should be done with every oil change, so if you follow the manual, you should be doing em about every 5000-7500km. i personally cant be assed resetting my radio settings and disabling the alarm to remove the battery, ripping out my cold air intake and flipping my windscreen washer out of the way that often.