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01-12-2014, 09:47 AM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Quote:
Originally Posted by N395V
Now if I can just keep low sulfur diesel from destroying my Superduty Powerstroke by adding ATF to every tank of fuel. Several mechanics have told me this is the problem and the cure.
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10% bio fuel.
__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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01-12-2014, 10:31 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by Toobuilder
If Lycoming endorses running at peak EGT (factory endorsed = "good"), then how can running cooler (LOP) be "bad"?
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Not saying there is a problem, but . . .
There is more to the discussion that just temperatures. Oxygen content of the exhaust goes up with leaning. Cars are limited to 3% due to keep the catalytic converters functioning properly. We can run higher (oxygen and much cooler) if the lean combustion stability remains good. IF and IF there were an exhaust valve material that was sensitive to oxidation at those temps then it could be worse.
I don't know what exhaust head materials are being used, but Continental always recommended the leaner the better, as long as the engine remained running smooth.
Large natural gas engines greatly extended their life by going very lean and getting near diesel exhaust temps. Valve materials last much much longer with cooler operation.
Just for the record. I plan on running LOP, as much as I can get it.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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01-12-2014, 10:38 AM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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Quote:
Originally Posted by rocketbob
No because the exhaust valve has a stellite-coated rotator cap.
Hence the name! 
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Bob... the rotator cap rotates though... correct?
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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01-12-2014, 10:45 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.
Of course with no cats on aircraft, I'd like to hear if there is any composition of the exhaust gasses that is harmful to exhaust valves. If it is something other than simply a matter of temperature and contaminants, I'd like to know. Both of which are lower at LOP than the peak setting endorsed by Lycoming.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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01-12-2014, 11:07 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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My pea brain has accumulated some facts over the years and here's what I believe to be true concerning LOP:
1) Lycoming does not list an upper limit for EGT on non-turbo engines (turbo is 1600, but that is limited to keep the turbo alive)
2) Lycoming allows running continuously (in cruise) at "peak" EGT (in other words, as hot as your engine will make the EGT go)
3) lead, carbon, trash in the fuel and poor machining will prevent the exhaust valve from seating fully and limit the transfer of thermal load to the head, causing local overheating of the valve and failure.
4) LOP EGT is by definition cooler than allowed by the factory, results in less fuel (and by default, less lead, carbon and trash in the exhaust), and because of the lower energy of combustion, lower CHT.
If the above 4 factors are true, what additional factors make LOP ops "bad" or "damaging"? I'm not talking about poor engine management skills, I'm talking specifically "LOP causes damage because of..."
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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01-12-2014, 11:24 AM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by Toobuilder
Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.
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Probably more so to keep the pistons alive. Usually over rich mixtures cause higher Cat temps as the fuel lights off inside. There is a tricky balancing act between piston and Cat life with regards to WOT AFRs.
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01-12-2014, 12:43 PM
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Forum Peruser
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Join Date: Jan 2005
Location: Austinville, Alabama
Posts: 2,458
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What else has changed?
My sincerest apologies to Mr. Freitag. While trying to post a reply, watch NFL TV and type on an iPad, I somehow deleted most of his post. Would Mr. Freitag please re-post as best as he can remember? Again, my apologies to Mr. Freitag, Sincerely and feeling like a dunce, Don Hull
__________________
Don Hull
RV-7 Wings
KDCU Pryor Field
Pilots'n Paws Pilot
N79599/ADS-B In and Out...and I like it!
?Certainly, travel is more than the seeing of sights;
it is a change that goes on, deep and permanent, in the ideas of living." Miriam Beard
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01-12-2014, 01:00 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by Toobuilder
Agree that cats in cars are a very temperature sensitive thing. Need to be hot enough to light off the catalytic cycle, but not so hot they melt down. Many computer controlled cars will smoke pretty good at WOT. My Corvette will do this sometimes and it's the computer dumping extra fuel to keep the cats alive.
Of course with no cats on aircraft, I'd like to hear if there is any composition of the exhaust gasses that is harmful to exhaust valves. If it is something other than simply a matter of temperature and contaminants, I'd like to know. Both of which are lower at LOP than the peak setting endorsed by Lycoming.
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Sorry not to be crystal clear - it is OXYGEN OXYGEN OXYGEN is the difference as the hot mixture goes LOP. The fuel burn goes from a carburizing flame to oxidizing flame.
Full load enrichment on the Vett is for power. More fuel across the catalyst will not BURN because there is NO OXYGEN. Many cars have this. It is not to "protect" the catalyst. Lets not get off track.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
Last edited by BillL : 01-12-2014 at 03:17 PM.
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01-12-2014, 02:04 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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So, does the gaseous makeup of the exhaust contribute to valve distress, or is it simply temperature (and/or the impurities which prevent the physically prevent the valve from transferring its heat load to the head/fins/air)?
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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01-12-2014, 02:50 PM
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Join Date: Jun 2006
Location: 8I3
Posts: 3,564
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Quote:
Originally Posted by az_gila
Bob... the rotator cap rotates though... correct?
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Yes it does, and so does the spring, seat, keepers, etc.
__________________
Please don't PM me! Email only!
Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
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