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Old 02-07-2019, 02:59 PM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,445

Originally Posted by Nova RV View Post
Scott, I'm not questioning your analysis but how are lower CHTs bad unless they are so low the cylinders can't "expand" properly and not allow it to break in properly or cause increased wear? Lower temps within reason was always told to me as being a good or better thing.

My cut outs are similar to Keith's although slightly larger.

Yes, you can run too cool. However, I have no idea what is too cool on a lyc. There is a reason your water cooled engine has a thermostat. If your logic applied, a thermostat would not be necessary, just let it get as cool as it can. Automotive thermostats were put in place decades ago to keep temps up, not down.

Power is a function of heat. If the head is allowed to get too cool, you will unnecessarily lose combustion energy into the head instead of pushing the piston down. Engines are typically designed for an optimum level of heat loss through the head and ultimately optimum running head temps. There are other negative effects from running too cool, as well. CHTs are an indication of the balance between combustion temps, including combustion frequency and heat transfer from the head.

Ring seating has nothing to do with CHTs, nor does cylinder expansion. They are tied to cylinder wall temperature. The heads are aluminum and the cyl walls are steel. Very different heat diffusion rates. The cylinders also have different cooling fin design. I would not necessarily expect the barrel temps to follow a linear correlation with the heads and doubt that they do. However, I admittedly have no idea what the relationship looks like.

RV-6A / IO-320, Flying as of 8/2015
RV-10 in Phase I

Last edited by lr172 : 02-07-2019 at 03:12 PM.
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Old 02-07-2019, 04:32 PM
RV10inOz's Avatar
RV10inOz RV10inOz is offline
Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,186

From memory......Lycoming publish a number well below 200dF and TCM 225dF.

Interesting that TCM with their water cooled engine (a jacketed version of their normal engines) set the temp at 239.

David Brown

DYNON Authorised Dealer and Installer

The two best investments you can make, by any financial test, an EMS and APS!

Last edited by RV10inOz : 02-27-2019 at 03:52 PM. Reason: I retyped 225, when it was 239. Oops
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Old 02-07-2019, 05:07 PM
Nova RV Nova RV is offline
Join Date: Aug 2015
Location: Leesburg, VA
Posts: 404

Originally Posted by RV10inOz View Post
From memory......Lycoming publish a number well below 200dF and TCM 225dF.

Interesting that TCM with their water cooled engine (a jacketed version of their normal engines) set the temp at 225.
I found this in the IO 390 operation and installation manual, P.18

For maximum service life of the engine maintain cylinder head temperatures
between 150°F. and 435°F. during continuous operation.

Thanks for the reminder to go back to the manual for guidance !
Chris Moon
Leesburg, VA

CFI-I ASMEL, ATP, B-1900, A319/320, B-757/767, B-737, Flight Engineer-Turbojet

RV-14A kit # 140243 (flying as of 11/18)
VAF 2018 and 2019 paid

Last edited by Nova RV : 02-07-2019 at 07:32 PM. Reason: wrong page reference
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