wrote

There is a fundamental problem, any auto engine is designed to deliver
purely rotational power from the crankshaft to the transmission.
In aero applications the prop is applying the entire power of the engine
trying to pull the crankshaft forward out of the block. That needs some
serious thrust bearings which auto engines simply do not have.
True, but I believe the conversation was about PSRU equipped engines, in
which side loads on the crankshaft and thrust loads will have been taken
care of by the PSRU. (or should have in well engineered PSRU's)

A well engineered PSRU is a beast that has been mastered, many times. It is
not a black art, until you get into long shafts, and strange things like
that.

The other thing that will bite an auto engine package is the other stuff on
the engine. Alternators, uninterruptible power if voltage is needed for
ignition and or fuel pump, cooling and anything else mounted on the engine
necessary to keep it running.
--
Jim in NC