Definition
The narrow range of fuel-to-air mixture settings that produces the highest engine power output for a given throttle and RPM setting. It is slightly richer than the chemically perfect mixture, because the extra fuel cools the cylinders and allows the engine to develop maximum power without detonation.
Plain English
The mixture setting that gets the most power out of the engine. The pilot leans the fuel a little, but not too much — just enough to hit the sweet spot where the engine pulls hardest.
Context Anchor
Seen in climb and cruise performance charts, especially where the chart assumes the mixture has been set for power rather than fuel savings.
Derivation
Best power' simply means the mixture giving the greatest power output. The phrase is paired with 'best economy mixture,' which is leaner and gives the most miles per gallon rather than the most horsepower.
Why Pilots Care
Using this range during climb or high-power cruise gives the highest available power and prevents engine damage from an overly lean mixture.
Intuition Check
Do not read “best” as “best for everything.” Here, “best power” means best for producing engine power, not best for saving fuel or reducing engine temperature.
Example Sentence 1
During the climb, the pilot leaned the mixture to the best power range to maintain strong engine output at altitude.
Example Sentence 2
On the cruise performance chart, fuel flows listed in the best power mixture range are used when the pilot needs maximum speed rather than maximum endurance.