REFLECTOR: CHT's

[Scott Derrick]

John,

1&2 are the farthest from the propeller, or closest to the firewall. 

And I agree, trying to direct the air is like trying to push on a rope. 
Pulling works better which is what your additional cut out  in the lower
cowl does.  Thats whats weird because 1&2 are right below the duct from
the NACA and has the largest space between the lower cowl and the cylinders?

I would think opening up a space between the plenum and some of the
cylinders would allow more air to not go through the fins and thus raise
your overall cylinder temps?

Anybody with a IO550 have hotter 1&2 cylinders?

Scott

aminetech at bluefrog.com wrote:
> --- 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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