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high heats

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pitts_pilot(at)bellsouth.
Guest

Posted: Wed Dec 26, 2007 9:18 am Post subject: high heats

The 'timing' thread brought up high temps (CHTs and EGTs) which made me 

wonder too ...... I'm convinced that a sealed plenum over the engine, 

sealed well around the inlets, would go a long ways to get rid of the 

high temps.  Sealing to the cowl top with silicone or even the older 

reinforced fiberglas strips just seems archaic to me.  The differential 

pressure from the upper plenum to the lower cowl also makes a difference 

and could increase the cooling drag.  In the 'timing' thread, someone 

also brought up the problem of changing the timing to change the temps.  

IMHO, that's just masking the problem,  If you're comfortable with that, 

why not just remove the CHT and EGT guages?????  The timing is specified 

based on the cam profile and the intake/exhaust systems ability to 

breathe. Shutting off 1/2 of the spark plugs changes the flame front 

profile and robs your engine of power and efficiency.



So, my question is why don't more engines have the plenum baffling 

configuration???



Linn

do not archive

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JohnInReno

Joined: 08 Sep 2007
Posts: 150

Posted: Wed Dec 26, 2007 12:13 pm Post subject: high heats

Engine temps are a function of heat generated minus cooling efficiency. 

Heat generated is controlled by compression, fuel/air mixture, valve 

timing, and ignition timing. Cooling on an air-cooled engine is 

controlled by directing the air through the engine's cooling fins.



Correcting timing issues is not masking the problem. It is focusing on 

the heat generated side of the equation.



On the cooling side, I agree that a plenum is more elegant than baffling 

to the cowling. I suggest that you check out the Sam James cowling 

groups for more info. At the Van's Homecoming fly-in at Independence, OR 

this year, I think half of the RVs that live on that airport have a 

plenum. Somebody there made a mold and then ran off a bunch of copies 

for all his neighbors.



I decided to stick with the standard baffling for the following reasons:



1. I have a very pretty metallic blue engine built by Eagle Engines that 

I don't want to hide.

2. It is an IO 320 that generates less heat than some of the bigger engines.

3. A plenum captures more heat on top of the engine after shut-down. 

This can acerbate vapor lock problems with the fuel injection spider.



John Morgensen

RV-9A fuselage

Grumman AA1B-150 aka "RV Trainer" flying



linn Walters wrote:

 	  Quote: 	
		   



 The 'timing' thread brought up high temps (CHTs and EGTs) which made 

 me wonder too ...... I'm convinced that a sealed plenum over the 

 engine, sealed well around the inlets, would go a long ways to get rid 

 of the high temps.  Sealing to the cowl top with silicone or even the 

 older reinforced fiberglas strips just seems archaic to me.  The 

 differential pressure from the upper plenum to the lower cowl also 

 makes a difference and could increase the cooling drag.  In the 

 'timing' thread, someone also brought up the problem of changing the 

 timing to change the temps.  IMHO, that's just masking the problem,  

 If you're comfortable with that, why not just remove the CHT and EGT 

 guages?????  The timing is specified based on the cam profile and the 

 intake/exhaust systems ability to breathe. Shutting off 1/2 of the 

 spark plugs changes the flame front profile and robs your engine of 

 power and efficiency.



 So, my question is why don't more engines have the plenum baffling 

 configuration???



 Linn

 do not archive

- The Matronics RV-List Email Forum -

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:

http://www.matronics.com/Navigator?RV-List

_________________
John Morgensen
RV-9A - Born on July 3, 2013
RV4 - for sale

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