Here is a question to ask a Subaru normally aspirated engine owner.
What is your PSRU ratio and what RPM are you taking off at? If the answer
is much less than 6000 RPM and the PSRU ratio is much less than
2.2:1  (2700 prop RPM) then he is not getting 160 HP.

The 150 cubic inch NA Sube is about 160 HP at 6000 RPM.
That is why most Sube cars sold today are turbo charged.
160 HP is no longer competitive in the car market segment
(price) Subaru wants to be in.

Most Subaru s you find in aircraft are NA. They are lucky to
see 130 HP. As such they are probably pretty good aircraft
engines but not as good as a real air cooled aircraft engine.
The main problem I suspect is the exhaust valve material is not as
good as real aircraft engine exhaust valve material which of course
is the finest available. In the case of Lycoming it is sodium
cooled hollow valves. It is near impossible to put sodium cooled
valves in a Subaru engine due to space constraints. Sodium cooled
hollow valve stems are larger in diameter than solid stems.
Not to mention the cost of about $215 each. Here is a graph
from the Sky Ranch Engineering manual.

This would be a particularly severe problem for a turbo
charge Subaru engine running at continuous high power.

The average life of the major moving parts such as crank shafts
and rods, from a fatigue standpoint, remains to be seen.
Like any other piston engines there are a lot of reversing
stresses going on. The rotary on the other hand has no
reversing stresses.

Paul Lamar ...No rotor no motor.

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