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Old 31-07-2016, 11:16   #61
Guy
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Re: aviation gas for a 20hp yamaha

High and low compression are relative. High in an aircraft is still pretty low by auto standards. The only really high compression engine I can think of is a Lycoming helicopter engine and it is high, 10:1. The rest range from 7-8 maybe.
So what you do is, put helicopter pistons in your airplane engine and you get another 25hp!
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Old 31-07-2016, 11:55   #62
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Re: aviation gas for a 20hp yamaha

Lycoming > PRODUCTS > Engines > Certified > 540 Series > Engine Data

Lycoming 540's, a real common "big" motor, you'll notice highest compression ratio is 8.7 to 1.

Auto is commonly much higher, but have usually knock sensors, and never are run at full throttle for more than a few seconds, Autobahn excluded

Aircraft require a huge margin, cause your never want to detonate one to death or seize one for that matter.
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Old 31-07-2016, 13:05   #63
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Re: aviation gas for a 20hp yamaha

[QUOTE=a64pilot;2179063]

Lycoming 540's, a real common "big" motor, you'll notice highest compression ratio is 8.7 to 1.


Yeah and the compression ratio of your C-85 is 6.3:1.
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Old 31-07-2016, 13:46   #64
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Re: aviation gas for a 20hp yamaha

I'm partial to Continental motors IO-550-G 8.5:1 compression ratio.
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