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Acceptable CHT spread

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Mike Whisky

Joined: 05 Jun 2006
Posts: 336
Location: Switzerland

Posted: Sun Sep 07, 2014 12:20 pm Post subject: Acceptable CHT spread

Hi

I was wondering what CHT spread is acceptable in cruise. 

I currently have a spread if 32 between my hottest and coolest cylinder in LOP cruise. 

I understand that a spread of 0 would be the ultimate goal but what spread do other see in average. 



Mike

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#511

Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Sun Sep 07, 2014 12:34 pm Post subject: Acceptable CHT spread

Acceptable to whom? I would call your spread very acceptable if it is hottest to coolest. If it were plus or minus 30 some degrees I might try to get it a bit closer, but many certified planes are no better than that.



If you can get the EGT's to peak within 0.5gph or less, then CHT differences are going to mostly depend on baffling caused airflow differences. They can be fine tuned with the dams in front of #1 and #2 cylinders.



On Sun, Sep 7, 2014 at 1:20 PM, Mike Whisky <rv-10(at)wellenzohn.net (rv-10(at)wellenzohn.net)> wrote:

[quote]--> RV10-List message posted by: "Mike Whisky" <rv-10(at)wellenzohn.net (rv-10(at)wellenzohn.net)>

 

 Hi

 I was wondering what CHT spread is acceptable in cruise.

 I currently have a spread if 32 between my hottest and coolest cylinder in LOP cruise.

 I understand that a spread of 0 would be the ultimate goal but what spread do other see in average.

 

 Mike

 

 --------

 RV-10 builder (flying)

 #511

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=430163#430163

 

 

 

 

 

 

 

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Kelly McMullen
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jesse(at)saintaviation.co
Guest

Posted: Sun Sep 07, 2014 12:36 pm Post subject: Acceptable CHT spread

The most important thing is that all CHT's be within acceptable limits. After that, the lower the spread the better. In my experience 32 degrees is quite good. I wouldn't worry about getting them closer than that. If you have one or two that are significantly different (ie, 5 are within 5 degrees and one is 30 degrees out), then you could do a little something, but if all are in the mid 300's, then I'd leave it alone. 



Jesse Saint

Saint Aviation, Inc.

352-427-0285

jesse(at)saintaviation.com



Sent from my iPad



 	  Quote: 	
		   On Sep 7, 2014, at 4:20 PM, "Mike Whisky" <rv-10(at)wellenzohn.net> wrote:

 

 

 

 Hi

 I was wondering what CHT spread is acceptable in cruise. 

 I currently have a spread if 32 between my hottest and coolest cylinder in LOP cruise. 

 I understand that a spread of 0 would be the ultimate goal but what spread do other see in average. 

 

 Mike

 

 --------

 RV-10 builder (flying)

 #511

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=430163#430163

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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carl.froehlich(at)verizon
Guest

Posted: Sun Sep 07, 2014 1:49 pm Post subject: Acceptable CHT spread

Agree with all the comments.



Now for me, after injector balancing I have EGTs all peak within 0.2 GPH but

#3 CHT is always the hottest by 30 degrees on climb out, 25 degrees in LOP

cruise (#3 hottest, #4 coolest in both cases, the rest of the cylinders

within a few degrees of #4 CHT).   As #3 is in the middle, do I trim the

cylinder inter baffles that came with the engine to cool off #3 or what?



I already looked for casting flanges and such to clear between the cooling

fins on #3 - no joy.



Carl



--

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rv10flyer(at)live.com
Guest

Posted: Sun Sep 07, 2014 4:55 pm Post subject: Acceptable CHT spread

#3 for me as well, except my #3 is by far the coolest by 30F from the others 

on climb and within 5 degrees of #4 in cruise but still 30-40F off from #6 

my hottest.



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Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Sun Sep 07, 2014 6:06 pm Post subject: Acceptable CHT spread

Push the normalize button on the engine analyzer, if it has that feature, so they all appear to be same temp, and ignore the difference. There is no value in attempting to get it more balanced.



On Sun, Sep 7, 2014 at 2:49 PM, Carl Froehlich <carl.froehlich(at)verizon.net (carl.froehlich(at)verizon.net)> wrote:

[quote]--> RV10-List message posted by: "Carl Froehlich" <carl.froehlich(at)verizon.net (carl.froehlich(at)verizon.net)>

 

 Agree with all the comments.

 

 Now for me, after injector balancing I have EGTs all peak within 0.2 GPH but

 #3 CHT is always the hottest by 30 degrees on climb out, 25 degrees in LOP

 cruise (#3 hottest, #4 coolest in both cases, the rest of the cylinders

 within a few degrees of #4 CHT).   As #3 is in the middle, do I trim the

 cylinder inter baffles that came with the engine to cool off #3 or what?

 

 I already looked for casting flanges and such to clear between the cooling

 fins on #3 - no joy.

 

 Carl

 

 --

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
KCHD

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