David Carter wrote:

Following is quoted from
http://Home.InfoRamp.Net/~raac/CoolingSystems/Part2/Cooling
System2.HTML, which is "Part 2:  COOLING DUCT DESIGN" by Hans Mayer RAA,
MIdland Ontario Chapter):  "First the JUNKERS JU87.. the prototype
(JU87V 1) had a 525 HP supercharged Rolls-Royce Kestrel V engine with a
chin radiator.  [ right up close to prop ] The radiator intake was
nicely slanted, to improve cooling, (later you find out why) but the
engine was overheating.  Fig 2 ....   The [attempted] solution to the
problem as a big ugly forward set radiator.  In Figure 3 moving the
radiator made things worse, not better!!  The propeller is forcing the
air back, but by thrashing through the air it creates a lot of
turbulence and strong flow around the fuselage.  Every blade creates a
pulse when it comes by the radiator.  . . . So anything [radiator inlet
location ] three times the chord of the propeller blade [or less] . . .
is in that turbulent area and gets the pulse of the blade.. . .
Everytime a propeller blade sweeps by, a pulse is pushing in the duct,
instead of good continuous flow. . . . Finally, on the D model . . . the
designers located the radiator under the wing, and the oil cooler far
back on the chin, out of the propeller pulses. . . . This cooling system
worked well, even in Sicily and North Africa."  [ article gave other
examples ]

Jeff Spitzer posted an excellent outline of a "cooling system design
process" Feb 18th.  One sentence was,  "The best place for an inlet is
right behind the propeller (duh!)"   Intuitively, this would seem
reasonable.  WWII experience reported above indicates a need to qualify
"right behind" as being "at least 3 propeller blade chord lengths behind
prop", and the first place aft that the designers of low wing aircraft
came to that worked well for radiator was near the trailing edge of the
wing.  The oil cooler was left up forward on nose, but more than 3
chords aft.

David Carter, Nederland, Texas, Building RV-6

[ and planning to use 1990-91 non-turbo'd 13B which Chilton's says put
out 160hp at 7000 rpm, which required use of Mazda's "new inductions
system" (intake tuning) which everyone tends to discard and thereby
revert back to 140hp (lose 20 hp by not using full "stock" Mazda 1990-91
induction system, then wonder why not getting speeds comparable to
Lycoming powered RV's) ]

Yes but it is too heavy and won't fit under the cowl. You can certainly
get the same power with a properly tuned manifold configured to fit
under the cowl. Check the ACRE News Letter web site below.

PL
 
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