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.