Doug:

**Of interest, within the limits of my setup (VM1000, all altitude and engine parameters the same with the exception of a 15degF cooler OAT) I did notice a 20-30degF cooler CHT with the new Iridium plugs over a broad range of fuel flows, and a 2-3 knot improved speed at lean-of-peak operations (no change at ROP operations).**


I know of no scientific reason that the type of plug making the spark could make such differences. It's more likely the OAT. More O2 molecules for combustion and better air cooling. The improved LOP speed is O2 increases in the cooler air. It allows for more FF at a given LOP setting. If you were to set the same FF, the HP output and TAS would be the same. We must be careful to assign the correct cause for an observed change.

Walter