The Passion of Mixture

Peter Garrison

Thursday, May 09, 2013 at 12:28 AM ET

Verified

** As you lean the mixture, cylinders get hotter.
But they cool rapidly on the lean side of
peak EGT.**

Key Takeaways:

The article debunks the common misconception that running an aircraft engine with a leaner-than-peak exhaust gas temperature (EGT) mixture causes it to run hotter and leads to severe engine damage.
It clarifies that cylinder head temperature (CHT) actually peaks slightly rich of peak EGT and then significantly *decreases* when the mixture is leaned beyond peak EGT (Lean of Peak or LOP).
Historical factors, such as cooling practices for WWII-era supercharged engines and inadequate instrumentation or training, contributed to the widespread belief that rich mixtures are safer for engine health.
The author, like modern engine management companies, advocates for LOP operation in suitable engines, citing benefits like cooler cylinder heads and improved fuel efficiency.

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An incensed reader, reacting to my parenthetical remark “Making Range,” Technicalities, August 2012 that, contrary to widespread belief, a leaner-than-peak-EGT mixture reduces cylinder head temperatures, wrote:

_Maybe I am missing something, but it is against the laws of physics that a leaner mixture can run cooler, as the more dense the mixture, the cooler the chamber is, thus EGT rises when lean’d, so how can this be “contrary to widespread belief”? _