Originally Posted by rickair7777

For the average pilot, there is "properly leaned". This is typically about 50 degrees F rich of peak (ROP). This provides several benefits:

- Near-peak performance, which means good power and fuel economy.

- Cooler-then-peak temps, which reduces engine wear and possibly avoids catastrophic failure.

- Allows some "slop", or margin-of-error for cylinders which are not all getting EXACTLY the same fuel-air-mixture.

For the high-end operator, there is Lean-of-peak. LOP has these advantages:

- Very near-peak performance, for max power.

- Cooler-than-peak temps.

- Significant fuel savings due to being on the lean side of peak.