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The Passion of Mixture

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

Key Takeaways:

  • Contrary to a widespread belief, operating an aircraft engine Lean of Peak (LOP) Exhaust Gas Temperature (EGT) actually results in cooler Cylinder Head Temperatures (CHT) and improved fuel efficiency.
  • The misconception that lean mixtures invariably lead to engine damage originated from historical practices, such as running rich to cool highly supercharged WWII-era engines, and the challenge of uneven fuel distribution in some older engine designs.
  • Modern engine management, aided by proper EGT instrumentation and solutions like GAMIjectors for fuel distribution, allows for safe and effective LOP operation, contributing to better engine health and economy.
See a mistake? Contact us.

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”? _

Peter Garrison

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, ""Technicalities"" and ""Aftermath,"" with FLYING readers.

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