REFLECTOR: CHT's

[Rene Dugas]

I don't know what your naca to plenum looks like but mine is attached and no
diverter was needed.  All my CHT's are within 20 degrees.
Hope it helps somehow.
Rene'

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Sunday, October 18, 2009 3:10 PM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: CHT's

Flew this morning after plugging holes in the TCM/Cessna supplied "between
cylinder baffles".  I should have made my own, because the stock baffles
have huge holes in them.  They also don't wrap up around the sides of the
cylinders for optimal cooling flow. I may try to tighten things up a bit
more but it will require me to remove all the injection plumbing, spark plug
wiring and some other stuff.. 

Also adjusted the fuel map and smoothed out a few bumps in the oil cooler
exit duct.

The CHT's are really coming into a comfortable range.  Cruising at 165
KTAS(low power setting) they all stay below 360, but increasing power to
above 200 KTAS and  #2  climbed to 395, #1was about 365, the rest were all
below 330.  I'm mostly concerned with #2 but would like to see
#1 more inline with the other 4 as well.

I'm debating installing some kind of diverter(s) inside the plenum to direct
more air onto #1 & #2.  Anybody do that to lower CHT's with success?  How
did you do it?  Got pictures? Controlling air movement is such a funny
thing, sometimes what seems logical or intuitive is exactly the wrong thing
to do! 

The fuel map is as good as I will be able to get it, until I get the new
prop.  At least I am not running at peak EGT in RPMs above 2200 now. 
That helped the temps a whole lot.

Now to getting the oil temp down some more. Right now I am not running the
fan on the secondary cooler as I see it as a summer time auxiliary cooler.
With OAT in the 60's I shouldn't need it.  The oil temps were OK, but a bit
on the high side at a low power cruise speed of 165KTAS.
about 210F, but as soon as I fire-walled the throttle it started to come up
and seemed to stabilize at around 230, though I didn't stay at that power
setting more than a couple of minutes.  With the IO360 my current oil cooler
was good enough but marginal.  On hot days I had to step climb.  I don't
have an exit scoop or air dam on the exit duct.  The duct opening is flush
with the fuselage. I'm really intrigued with Don's idea of an Oil cooler
flap that can be adjusted from the cockpit. When flying with the IO360 I had
too much cooling in the winter and marginal in the summer. I would tape some
of the cooler face in the winter so my temps were hot enough to get a bit of
warm air in the cabin.  With a hinged controllable flap I could set it for
whatever the conditions were.  It would probably work out to 3 or 4 settings
that covered all scenarios.

Scott





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