I'm doing my first spark plug maintenance at 100 hours after install of a new set of Tempest UREM37BY spark plugs. They were installed at overhaul of my O-360-A1D without altering the gap set by the manufacturer (I think ~0.018?) to account for my Surefly SIM4N on the left side. I think Surefly recommends a gap of 0.022 to 0.035, favoring the high end of the range - not sure why, I think maybe because the longer duration spark otherwise causes excess wear? By contrast, the Bendix mag I have on the right side generally favors a 0.015-0.019 spark plug gap. My engine has run great for the first 100 hours SMOH with this setup, and just now there's starting to be slight roughness and occasional misses on the right mag at runup (without engine monitor anomalies). I think this makes sense since I see some of the plugs have worn past a 0.019 gap. Predictably there's a bit more wear on the plugs driven by the Surefly given the longer duration spark.
My question is: What would you do for plug rotation and gapping in this situation?? I can find no official guidance on this.. The standard rotation scheme will keep the Surefly and Bendix plugs separate throughout their life, which I think is desirable, except maybe the Surefly plugs will wear out faster leading to earlier plug replacement. However this keeps gapping much simpler - just let the Surefly plugs continue to wear into their optimal range while continuing to narrow the gap on the Bendix plugs as needed. Would anyone do anything different here?
My ignition setup:
1 2 3 4
TOP Bendix Surefly Bendix Surefly
BOTTOM Surefly Bendix Surefly Bendix