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pitts_pilot(at)bellsouth.
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 Posted: Wed Dec 26, 2007 9:18 am Post subject: high heats |
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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
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| Posted: Wed Dec 26, 2007 12:13 pm Post subject: high heats |
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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 |
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_________________
John Morgensen
RV-9A - Born on July 3, 2013
RV4 - for sale |
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