GTH wrote:
Michael Henry a écrit :

why isn't the Lycoming O-540 or the Continental O-520 an
inverted V?


They are derived from opposed engines, and the manufacturers thought
easier to retain the same cylinders and cylinder heads as their 4
cylinder counterparts.

OK so I just push my question back one generation: why is the O-360 not
an inverted V?

I'm asking more from a theoretical point of view. What is it that makes
the opposed configuration more attractive than the V configuration for
air-cooled engines? Likewise: what is it that makes the V configuration
more attractive than the opposed configuration for liquid-cooled engines?

There are new aircraft engine designs out the the Jabiru as an
air-cooled example and the Orenda as a liquid-cooled example. They
follow the same pattern that has become the norm.

There have been a number of aircooled inverted engines in the post WWII
period.

....and in the pre-WWII period! The deHavilland Gipsy Major being a
notable example.