Some common misunderstandings in dealing with an auto
conversion is that many people fail to take into
consideration certain factors, mainly one.  Say for
instance that you have an auto engine that develops
200HP at 6000RPM.  You are using a PSRU that has a 2:1
step down.  You'd think that would double your power,
nope.  You'll still only be getting 200HP output at
3000RPM, and that's assuming that you are getting 100%
efficiency from your PSRU.  No PSRU operates at 100%
efficiency.  Say for instance that you have a 20%
loss.  You now have a motor that in all essence is
equal to a 160HP direct drive motor with a 3000RPM
output.  20% may seem excessive.  But go look at some
of the PSRU manufacturers, this is not out of line. Upto 25% is fairly common.  Geared PSRU's typically
have a lower efficiency loss.  Say you want to replace
a I0-360 motor with a auto conversion.  You'd need to
make 210HP at 5500RPM with a 2:1 converter and 15%
PSRU loss to achieve the replacement output of the
I0-360 at 160HP.  If you are running an auto engine at
5500RPM, your fuel economy is fairly high for this
size motor.

It's been mentioned and some people have wondered why
Subaru motors have been pulled in favor of a Corvair
motor.  The Corvair motor does not have the
complicated systems associated with it that a liquid
cooled motor has to deal with.  It's aircooled like
most other aircraft engines.  It's power is generated
at a fairly low range, again like aircraft motors.  If
you had a Subaru running at 6000RPM with a 30% loss at
the PSRU it could output 160HP and still be equal to
the Big Bore version of the Corvair.  And the Corvair
would be much lighter and use up much less fuel.

I'm currently building one of these Corvair motors. Why?  Because I can <insert stupid smiley thing
here>!!!

Sometimes you have to look at your final operating
costs when considering the financial implications of
an auto conversion.

There's an engine that I've been watching for several
years now.  The company has finally started building
and selling these engines.  It's known as a Dyna-cam
motor.  It's about 265lbs. dry weight.  It outputs
200HP at a very low 2000RPM with a torque output of
525 ft lbs. at 2000RPM.  It's smaller than most
aircraft 4 cylinders.  It's deminsions are 13" x 40"
length.  Very streamlined.  This motor has even been
certified, although they are concentrating on the
experimental market at this time.  The engine is not
cheap by any means.  But I think that it will be
proven to be a very remarkable motor.  I'm personally
going to wait for the diesel version of this motor.

Just trying to throw some input into the debate.
Bill

 Homepage:  http://www.flyrotary.com/
 Archive:   http://lancaironline.net/lists/flyrotary/List.html