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.
Paul, I don't care if you post this - just playing devil's advocate
here...
I don't know much about Subaru engines, but I do know that lots of
turbocharged car engines have sodium cooled valves. We have a Volvo
with them.. 200k+ miles and doesn't burn any oil. 'Course we don't
run it that hard - 3000rpm is 68mph in OD..
Matt-
68 MPH is also less than 50 HP.
Interesting Matt. Volvo has a history of building bullet prof
engines. They were still using forged cranks and rods after
most other manufacturers had long gone to cast iron. Klaus
loves them owning several old ones. What year is yours?
I could be wrong. The new Subes might have sodium cooled
exhaust valves. I wonder why air cooled VW's never used them.
They sure needed them.
--
Paul Lamar ...No rotor no motor.
True about the horsepower... Not much required for highway use..
We have had 5 Volvos.. Still have 2 of them. The old one is a '67 122s
and the newest is an '82 245GLT.. I drove a '74 145E while in
college.. A good little car. In some ways I wish I still had it. The
toughest thing is finding someone who is competent and honest to work on
them..
The early Volvo engines had cranks with as much main bearing area as a
350 Chevy.. Weaknesses of the early engine were cheesy Bosch
distributor (actually not that bad), horrible SU (or Stromberg carbs),
and the cam was driven by a fiber gear meshed with a steel gear. The
cam gear was actually okay as long as you didn't go crazy with a lot of
cam lift...
Matt-
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