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Engine Compression Ratio at 8.7:1 On Lycoming IO - 540

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HomeBuilt101

Well-Known Member
Joined
Oct 20, 2015
Messages
384
Location
Aguila AZ
I just realized that the Lycoming non- turbocharged engine has a compression ratio of only 8.7 - 1.

I'm curious why these engines need 100 octane AVGAS because in car applications, where high octane pump fuel is around 93 octane, these engines have way higher compression ratio than that and they turn upwards of 6000 RPM at times.

Why did these engines need such high octane?
 
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