· Premium Member
The AC-Delco 41-121 are the NGK 6 heat range OEM plugs. The 41-122 are the NGK 7 heat range OEM plugs. Which copper plugs did you try. I've had good experience (other than longevity) with the NGK vPower BRK7E and I just finished my first full day with the NGK BRK8E plugs. I've also had the NGK OEM plugs (AC Delco 41-122) and the NGK BRK7IEX iridium plugs and the BRK8Es are by far the best plugs I've had so far.