veedubber and others
the venerable old VW engine conversion is quite usable.

if you were to take all the lessons learnt from all the engine
building done so far and apply them to a new engine design, what would
the new engine design look like?

I think the flat 4 makes a very serviceable aircraft engine.
underslung pushrods like the O-200 and VW would remain.
I'd use hydraulic lifters.
the castings for the crankcase would be simpler, more like the O-200
than the complexities of the VW casing.
the crankshaft would be a little more robust at the front end
I'd fin the pushrod tubes and use the oil returning to the crankcase
as a radiator.
the engine would be mounted on dynafocal lord mounts.
I'd use electron for the crankcasings.
spin on oil filter. (z79)
magnet in the sumpplug.

what else???

Stealth Pilot