<<George is wrong.
If you can open up a 1.5 inch hole in your baffling and see no change in the
cooling of your air cooled engine in all regimes it was meant to effectively
operate, you have an inefficient cooling system.  You have way too much air
coming in and have created a high cooling drag situation...best power that
the engine was designed for and is capable of delivering forever...
Scott Krueger>>

Well, yes, no, maybe and probably not.  As an engineer I object to people
giving human qualities to inanimate objects.  An engine is nothing more than
a collection of iron, aluminum and bolts - it has absolutely no clue what it
was "designed for."  While the designers certainly designed it to last as
long as possible under all conditions forever is a long time.  And since
higher temperatures reduce strength and creep qualities it can be expected
that running at higher temps and pressures will reduce engine life.  And,
yes, installing a 1.5 inch "leak" in the cowling will reduce efficiency, but
as George says, it can show that it doesn't effect cooling all that much.
However, there isn't "too much air coming in" as all the air that comes in
goes out and the objective is to make sure that all the air that does flow
through does something useful.  It is a sign that the air inlets are too
large for that particular operating condition.  At low speeds the engine
might want the extra inlet area.  Maybe.  Also, I find it interesting how
much attention is usually paid to inlet area (except for Lancairs, it
seems).  A properly designed inlet doesn't reduce efficiency by much if it
is too large as the pressure in front of it will just push air around the
sides and if they are generously radiused there will be very little
associated drag.  The Lancair cowl is a good example of this.  One of the
fastest piston engined planes built at the time was the Corsair and look at
the huge cooling inlet.  The cowling was radiused to provide for a smooth
flow around the outside and that is what mattered.  The prop hub was then in
a relatively stagnant area and thus didn't need a spinner.

Just some observations

Gary Casey
ES