REFLECTOR: CHT's

aminetech at bluefrog.com aminetech at bluefrog.com
Sun Oct 18 17:20:52 CDT 2009



--- scott at tnstaafl.net wrote:



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! 

That's what I found with my Franklin.  First of all, where are your #1 and 2?  Front or back?  My back cylinders (#5 & #6) ran hotter than the rest.  Baffling didn't help.  I think the air will take the least path of resistance in spite of where you try to send it.  What worked for me was putting spacers between the plenum and back cylinders to allow more air to pass by.  It helped a lot.  I also made a cut out in the bottom cowl just aft of the oil pan because there is a gap between the cowl and the intake scoop and I felt that ingressing air was combining with the exiting engine cooling air and congesting at that point.  Sometimes my CHTs read identical and sometimes there's a 10-20 degree difference.  No idea why it changes, but close enough I think.

John


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