On Aug 27, 8:24 pm, "
wrote:
the isolation of prop loads on a crankshaft that IS
NOT DESIGNED to take prop loads.

This is the kind of problem I was fishing for in the original post --
something I hadn't heard of, but constitutes a show-stopper.

I like that two-into-one spark plug idea. If that's feasible, I'm a
LOT less attached to magnetos.

It's feasible and done on several conversions, like the RAF Soob
setup.

could a GM engine attached to a short manual trans 1-get a dry sump
and 2-be flipped upside down and have a stout racing trans take the
loads. i'm thinking the dry sump/upside down engine makes a more
normal looking cowling. I vaguely recall piston luftwaffe planes
having inverted Vs.

Steve Wittman did it with the aluminum Buick V-8, direct drive.
The buick was a rather small V-8 of around 260 cubes, and was pretty
light, too. Steve's Tailwind was designed to fly on engines of 85 to
150 hp, and the Buick was able to produce, IIRC, around 120 hp. Dry
sump, though the Buick's crankcase is a lot different than any
inverted V's (or inverted inlines) built for aircraft, which have the
cylinders separate from the case instead of cast in, and those
cylinders extend into the case a little to prevent most of the oil
draining into them. The Buick would have some difficulty with that.

as for not getting your money's (or weights) worth of hp running a
502hp Gm engine at 1/2 redline, remind me again, how much does an
O-720 cost, weigh, and what hp does it put out?

Let me tell you: The owner of the Glastar, by the time we got
that 130-hp Soob converted and running and installed so that it would
work, spent AS MUCH as the Lycoming that was recommended for the
airplane, and its resale value when it sold was only about ONE THIRD
of what Lyc-powered Glastars were going for. How's that for a cost
comparison? And the Glastar's Soob cannot run at its redline of 5600
or anywhere near it for cruise, or it'll burn too much fuel and will
wear out at an accelerated rate. It needed to cruise at no more than
about 4700, so with the fixed-pitch prop we'd given up a huge amount
of cruise speed. The airplane cruised at 110 MPH; with a 125 Lyc it
would have cruised at 135 or so. The Lyc redlines at 2700 and is
certified to run at that RPM its whole life, but most people will
cruise around 2500. 2500/2700 is a lot better ratio than 4700/5600. I
did much of the test flying of that Glastar and wished it had the Lyc.
The noise was awesome. At redline we achieved the design max cruise,
so we knew the engine was developing its claimed hp, but the noise
became scary indeed. Quite a howl.
Let me tell you this, too: Many homebuilders have spent a lot of
money converting some engine, only to find that they now have one or
more of the following: (1) CG problems, (2) less HP than anticipated,
(3) strange vibration issues, (4) cooling issues, (5) reliability
issues often related to the redrive or crank strength or ignition or
fuel systems, (6) vast cost overruns, and/or (7) in the end they tear
it all out and install an aircraft engine because they're finally fed
up with tinkering and want to go flying.
Unless you're a mechanical engineer or want to pour half your
life and most of your earnings into a one-off conversion, you're
better off with the aircraft engine or a well-proven conversion.
As for the IO-720: better to install a small turbine if you're
wealthy enough to build an airplane that needs 400 HP.

Dan