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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:

  • The article refutes the widespread belief that leaner-than-peak Exhaust Gas Temperature (EGT) mixtures increase cylinder head temperatures (CHT) and cause engine damage; in fact, CHT decreases significantly when operating lean of peak (LOP).
  • Key engine parameters like power output, CHT, and fuel efficiency peak at different mixture settings relative to peak EGT, with the highest CHT occurring slightly rich of peak and then dropping sharply on the lean side.
  • The misconception about rich mixtures being safer stems from historical contexts like WWII-era supercharged engines and traditional flight training, but modern understanding and technology support LOP operation for cooler cylinders and improved fuel efficiency.
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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