I’m of the camp that standard NGK BR8ES plugs is the best value. I have experience with an RV-14 running Iridium plugs and found no difference in performance. With dual pMags running BR8ES plugs I can go deep into LOP, to the point of engine cut out, with no roughness at all.
Note: Smooth LOP operation is also dependent on how well you balance your injector nozzles. On my IO-360-M1B I changed out two of them and enjoy a GAMI spread of 0.0 to 0.1 GPH. Replacement nozzles of various sizes are available from AirFlow Performance for ~$28 each - and Don will help you on what sizes to get.
And the BR8ES plugs are so cheap I just replace them every year or so instead of cleaning.
Last edited by Carl Froehlich : 12-14-2020 at 03:48 PM.