Reply-To: <glcasey@gte.net>
Reply-To: lancair.list@olsusa.com
From: "Gary Casey" <glcasey@gte.net>
To: <lancair.list@olsusa.com>
Subject: Chevy V-8 engines
Date: Thu, 3 Jan 2002 06:21:27 -0800
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>><<<...I would like to run the engine at 2800 rpm, the highest rated speed
published by MT (they don't seem to be willing to budge from the 2800 rpm
limit)....>>>

There are several good reasons for that.

<<<...With a compression ratio of 8.5 to 9, I expect that the peak cylinder
pressures will be only 10% higher than in an automotive application....>>>
                                                           AND
<<<...I hope to run a full-power manifold pressure of 40 inches, but in real
life I expect 45....>>>

>>The mechanical compression ratio alone isn't much good at predicting peak
cylinder pressures. Other significant factors include: inlet air density
(function of MAP and inlet air temperature), camshaft lift, duration,
lobe-spacing; intake flow path characteristics, and several more.

<<<...At cruise power the engine mechanical and thermal loading will be
about
the same as your average truck engine at 60mph ...>>>

>>I'd really like to see those numbers. "AVERAGE TRUCK ENGINE" is awfully
vague. Numbers are far less so.<<

Jack brings up some good questions here and I could reply off-line, but
given the encouragement lately I will "spill the beans" and accept the
ridicule on-line...

The idea for a direct-drive V-8 is based on the desire for a simple,
lightweight and flat-rated powerplant - and one that is fun to build.

The single-turbocharged after- cooled engine would use no real "high-tech"
components and the only aftermarket parts will be the aluminum block and
forged (or billet) crank.  The cam might be custom-ground to reduce valve
opening duration so that torque can be optimized at 2700 - 2800 rpm.
Displacement is between 400 and 420 cu. in. and the crank will use the "400"
main bearing diameters to maximize overlap between main and rod journals.
My previous comment about truck engines relates to the experience that a
large-bore automotive engine with a modest compression ratio of, say 9 or
9.5, will have a very long life expectancy running at 2700
wide-open-throttle (WOT).  That matches our experience at Mercury Marine
where we were lucky to get 150 hours at 4800 rpm continuous, but never wore
one out at less than 3,000.  At 5200 we figure 50 hours and the valve train
was always the failure point (we always ran the engines continuous and never
cycled the load).  2700/30 inches is pretty much the "75%" power condition
for the aircraft version.  I expect the weak links in the Chevy engine will
be the exhaust valves and head gaskets and that is why I would expect to do
a valve job twice as often as a major.

Mounting the propeller direct to the crank is another issue and on this I
looked at airboat experience.  The heresy evidence I got said that metal
propellers on airboats broke cranks "all the time."  Apparently now IVO
props are the hot setup in Florida and there "has never been a crank failure
in an airboat with an IVO prop." (okay, you can guess who said that)  An
airboat subjects the engine to much, much higher yaw and pitch rates than
could ever be experienced in an aircraft (not sure about a high-rpm snap
roll) so I figure if it works in an airboat it should work in a plane.
Pretty scientific, huh?  Anyone know the design yaw (or pitch) rate of an
aircraft and/or airboat?  Although I don't have the actual numbers think the
inertia of the MT would be roughly equivalent to an IVO so I plan to use the
MT with electric pitch control.  Therefore, I expect bending loads on the
crank will not be excessive.

Maybe the only real question left is the thrust bearing capacity.  The
maximum pressure figures out to be about 600 psi (1200 lb thrust, 2 sq. in.
area) and I don't have a good idea about whether that is a reasonable number
for a flat bearing or not - Haven't looked in my bearing design book yet.  I
expect to drill extra oil supply holes to the thrust bearing as the standard
design just uses the squeeze-out from the main bearing to provide the oil
supply.  There is not an easy way to increase bearing area on these engines.
I am not worried about the bearing areas or stresses for the main and rod
journals.

I have a design roughed out that will mount the engine on the same mount as
a Locoing IO-540.  The Continental engine mounts would go right in the
middle of the cylinder heads so that option is out.  Those mounts would work
with the engine right-side up, but the bulge on the cowl would be, well,
REALLY ugly or the prop clearance would be nil.  As it is, the prop
centerline will likely be 2 inches higher and the flange about 5 inches back
from the standard location.  I do not plan to use an extension on the crank,
only an adaptor that will bring the flange a couple of inches forward from
the crank flange.  The whole engine could be moved forward, but the CG is
already slightly forward from the standard installation and I'm told that
the CG on the ES is already too far forward.

So there it is, take your best shot.  I can always put a Continental in
it...

Gary Casey
ES project


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