Lean of Peak operation

[Walter Atkinson]

If flying NA, optimal leaning to LOP from Best Power will gain you a 3 gph fuel savings (per engine) and cost you 3 knots. If you are losing more than 3-4 knots, the leaning is farther LOP than optimal. It's not hurting anything, but you are giving up performance.

If turbocharged, you can save fuel AND go faster than when ROP because the CHTs are better controlled.

How far LOP one should set the optimal mixture depends on the power being produced. It's a straight-line variation from about 15dF LOP at 60% power to about 90dF LOP at 90% power.