Roger Halstead wrote in message I wonder why they use such a low
compression ratio? Even car engines
running regular usually run 8:1. This one is 6.3:1.
It would reduce the stress on the parts, allowing less expensive
materials than a reliable high compression engine.

Durability is one reason. Additionally, the typical bore and stroke in
aircraft engines is much larger than automotive engines. I forget exactly
why the larger bore and stroke is more susceptable to detonation, but I seem
to recall it has something to do the ratio of quench area to fuel/air charge
decreasing as the cylinder size increases.

D.