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Old 06-12-2019, 12:19 PM
AndyRV7's Avatar
AndyRV7 AndyRV7 is offline
Join Date: Sep 2007
Location: Hudson County, NJ
Posts: 1,048

Originally Posted by N804RV View Post
He did say he had a carb. LOP operations date back to WWII. And, Lycoming's recommendations haven't changed.
I don't know any history on this but I am guessing LOP was for a whole different reason back then.
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Old 06-12-2019, 01:00 PM
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gmcjetpilot gmcjetpilot is offline
Join Date: Jan 2005
Posts: 3,919

Originally Posted by AndyRV7 View Post
My RV-7 has a carb, with CHT and EGT information for each cylinder, in the panel.
Consider someday calibrating your probes. Also location of EGT probe from the exhaust port makes a difference. I assume they are equivalent. The closer to exhaust port within reason the better. However the closer they are the shorter life they will have.

Your guide to leaning

I've never relied on the EGT because they vary by 100-200 degrees maybe. My cylinder head temps are spread over a smaller range though and I never have a need to climb-out much hotter than 380 degrees (maybe 400 degrees in a short climb on a 90 degree day). Typically my cruise temps are below 350 on the hottest summer days, maybe lower.
350F CHT is low but OT (oil temp) is really important. You need at minimum 180F. The temps in the valve area are about 30F higher. You need at least 212F oil to burn off the moisture and acids. [NOTE: To balance out EGT's consider just closing the throttle just a tiny bit to create more turbulence and/or use a little carb heat. The Carb heat door slightly closed will also create turbulence in the air box... this can balance out the cylinders. AGAIN calibrate your EGT probes and assure they are equal distance from exhaust port.]

If I remember correctly, the problem (or one of the problems) with high CHT's is the pressure inside the cylinder. So every time I lean for cruise and look down and see 320 or so on the CHT's I always wondered if I was wasting fuel and could lean further while watching the CHT's for a more accurate but safe level of leaning.
Pressure has to do with detonation which can cause catastrophic damage to the piston and valves with out much indication to pilot. CHT really does not indicate cylinder pressure. The only thing that indicates max combustion pressure is very sophisticated pressure transducers, typically only used in test cells. It is not easy even then to get combustion pressure. The key is not to lean above 75% power to avoid detonation. If CHT is too cold (assuming it is calibrated) then operate at max power mixture. EGT absolute value does not matter. EGT is only relevant to difference or delta from peak EGT. [Note: cars have detonation sensors which are microphones listening for the knock. Aircraft engines being air cooled and loud make hearing detonation near impossible. Cars also have ECU mapping that knows RPM, Torque (thus power) and Fuel, so it can keep you out of danger. For airplanes the pilot is the ECU.]

As you know you lean until the first cylinder peaks and starts to go back down (all other cylinders are cooler on ROP side). If you have EGT probes way down the pipe it may take some time for them to respond, take your time. You can run PEAK if you want, but you are not at Max power (and max CHT). Max CHT is around +30-50F ROP and max power power is about 100F ROP. The more ROP +150F the cooloer. This will give you the hottest CHT (approx). If you want to cool it 50F ROP is good. Anything more than 100F is wasting fuel (in my opinion). Keep in mind some cylinder EGT's will be cooler. You can operate right at ROP or 40F ROP, if CHT's are not above 380F (my personal limit) and OT are not above 220F. Can you have detonation issues? Not if under 75% power and using 100LL (assuming all your temps are normal CHT<400F, OT<220F). I would not get aggressive with leaning (less than 75F ROP) until 65% power. Again it depends on CHT and OT. Again calibrate your probes.
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RV-4, RV-7, ATP, CFII, MEI, 737/757/767

Last edited by gmcjetpilot : 06-20-2019 at 12:10 PM.
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Old 06-12-2019, 09:07 PM
Mconner7 Mconner7 is offline
Join Date: Feb 2018
Location: Bradenton FL
Posts: 58

I lean aggressively in the O-540 in my -10. I have a 6 cylinder Garmin engine monitor and seldom ask for more than 60% power. Since I cruise up to 17,500’ on longer legs, it sure helps to have the instrumentation to see that reducing the throttle about an inch and modulating the carb heat can let me get the EGT’s balanced better and run more efficiently if only a little lean of peak.
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Old 06-12-2019, 09:21 PM
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Dbro172 Dbro172 is offline
Join Date: Apr 2012
Location: West Fargo, ND
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Default Carb heat trick

Another trick with a carb is to add a bit of carb heat in cruise to bring the EGT’s closer together and lean further. I believe, the carb heat baffle in the air intake box when partially closed (not much) disrupts the airflow enough to better mix the fuel air and deflect it more evenly to each cylinder. You will also notice that EGT/CHT varies based on throttle position and how the butterfly in the carb is deflecting air towards different cylinders. Like mentioned above, pull the throttle off the stop just enough to barely lower, or not even lower the manifold pressure. In my 0-320, I can run LOP at 65% power or less, with about 1” of carb heat pulled out and the throttle off the stop.
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Old 06-13-2019, 04:41 AM
Foghorn Foghorn is offline
Join Date: Feb 2018
Location: Virginia Beach
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Originally Posted by Dbro172 View Post
Another trick with a carb is to add a bit of carb heat in cruise to bring the EGT’s closer together and lean further.
This is good advice! I have a carb heat temp gauge and after leaning the mixture bring the carb temp up to 80*-100*. Engine runs smooth and you can "hear/feel" the slight increase in power.
Jeff Parker
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