Bob writes; Can you quantify how much the cooling was improved?
Did you notice changes in ground cooling, climb, cruise?
-bob

Bob,

My airplane was out of service for over a year during the time which I built
the plenum in exchange for the baffles.  To begin to think I had repeatable
provable data based on converting to the plenum would be only a guess as I
mentioned my motivation was more maintainability than temperature reduction.
I also sealed the daylights out of the tiny little leak areas with RTV.
This may frustrate some maintainers (according to GAMI) but I believe saves
a few degrees at Race Power which far outweighs any frustration of my
mechanic (me).

Todays plenum data is as follows.
Ground Cooling - Never look, can't even warm up the CHTs
Climb - I climb at 150 kts or above based on over the nose visibility.  This
provides continuously increasing CHTs from T/O to level off of approximately
300 - 390 F.
Cruise - I don't know (approx 350), depending on wallet size.  I like to
cruise at about 8 gph and 190 kts.

And the only data that really matters:

Race Power @ Sea Level (twist'm in an break'm off) 31" 2700 rpm 17 gph 380F,
oil temp 221F  
yields 215 kts  +/- depending on OAT, humidity, and airspeed
instrument trusted most.

Sorry I can't be more precise regarding conversion data.

On the other hand, if you are asking if converting from baffles to a plenum
will save the day in the heating department, I doubt it. Beyond gaping holes
in the baffling, my exposure to hot 360's has been problematic in a whole
nuther department.  That is, many 360's left the cowl inlets at the original
320 factory size (about 3.5"?).  This, IMHO, is the bigger CHT cooling
limiter (again for the 360s) that I've seen.  I have inlets of approximately
4.5" dia. These two inlets feed the cylinders and oil cooler just fine.

Two other factors which may influence my CHTS compared to yours are exhaust
pipes and lower inner aft baffles.  My exhaust pipes after approximately 20
mod/ repairs/ adjustments are exiting at the cowl edge.  This lack of
protrusion (and downturn) may provide some eduction affect.  There is more
analysis desired in this department and ongoing plans for a formal
augmentor.  Much SS has been added for heat protection.  

The Lower Inner Aft Baffle is a 3 part sheet guiding all cooling air
smoothly toward the exits. This is believed to be an eddy current reducer
that may or may not help my CHTs (it also acts as a heat shield for
gascolator, fuel pump, battery, and other firewall components). Of course it
too has maintainer challenges such as exhaust pipe hanger through holes.

Hope this helps.

Larry


> On Mon, 03 Sep 2007 13:00:00 -0400, LHenney wrote
<snip>
>  I built my baffles twice before shifting to a cooling plenum
> (duct) out of frustration with that contact damage. In addition
> to better cooling ( big factor!), the plenum allowed rounded
> edges, smoother contact surfaces, and overall less maintenance.
>
> Larry
> N360LH