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TOPIC: carb temps

carb temps 8 months 2 weeks ago #843

  • STEVE ELLS
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Hi Omar;
Since you're gathering data on the John Jewell HP increase, I suggest you write up your findings and I'll do my best to get them printed in the CPA magazine. We're always looking for more operating and piloting experience articles.
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carb temps 8 months 2 weeks ago #842

Steve,

Thanks for a great reply.

Now that I have been flying my C-182J for two years, I feel I am comfortable with knowing what is nominal for the plane. You're not the first to suggest a little carb heat to dampen the large differences in EGT; so I'm going to start trying that from now on.

I have been collecting climb/cruise performance numbers on the plane, as the John Jewel mod increased the HP to 252; so, the OEM charts may or may not be correct. Also, I have just subscribed to the full SavvyAnalysis service, and have already sent them a test flight profile record to start as a baseline.

Time to start squeezing every knot I can out of every drop of 100LL !


Omar
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carb temps 8 months 2 weeks ago #841

  • STEVE ELLS
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Since you didn't specify whether your engine is carbureted or fuel injected I'll pass on what I know about carbureted engines.I fly behind a carbureted engine. I used to fly a Cessna 182 with a carbureted O470 R engine. After I installed a 6 cylinder engine monitor I discovered that there was a large spread between EGT numbers. When the first cylinder would peak, there were cylinders that were still very rich of peak; in some cases more than 100 degrees rich.
I started looking for answers and learned that distributing equal amounts of the fuel air mixture to each cylinder was never part of the design process in the induction systems on the carbureted Continental engines. I learned that there were two actions I could take to better distribute the fuel air mixture. First, instead of running the engine with the throttle fully in; pull it out slightly until the MAP just wavers. This cocks the throttle plate in the carburetor which in turn creates more (relative to an all in streamlned plate position) turbulence which helps create a more even distribution of the fuel/air mix. Second, I could add partial carburetor heat to further aid the formation of a more uniform mixture. Since my 182 had a carburetor temp gauge I chose 50 deg F (10 deg C). I found that adding carb heat made such a difference that I had to re adjust the mixture.
The issue of shock cooling is either a non issue or a big deal; depending on who you listen to. Skydiving airplanes should be prime candidates for engine damage due to shock cooling; after all skydiving airplanes make money by hauling jumpers to altitude. More hauls equals more money. Time spent getting back down isn't earning any money so skydiver airplanes descend quickly. The pilots don't pull the power completely off but they reduce power beyond the suggestion of never reducing power more that 2 inches manifold pressure every 5 minutes.
I always try to gently apply power (never pushing the throttle fully in until the airspeed reads 30 mph) and pull power off gradually.
From what I have learned the quality of your cooling baffle sheet metal and baffle seals is the most important step you can take to reduce cylinder problems.
I'll research this more to see if I can find definitive advice on shock cooling. In the mean time fly in a way that keeps CHTs below 400 deg F and you'll probably be OK.
Last Edit: 8 months 2 weeks ago by STEVE ELLS. Reason: include clarifying sentence
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The following user(s) said Thank You: John "Omar" Bradley

carb temps 8 months 2 weeks ago #840

Trying to be more diligent about monitoring my JPI EDM for information other than EGT's and CHT's. What is the ideal range for carb temperatures? Also, what cylinder temp should alert me to shock cooling?
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