Lean of Peak Operation

[skylor]

Smooth

Ditto.

My first thought was that this is like letting out the clutch and going WOT on a 4 cylinder engine at 1800 RPM. Some lighter-built car engines (like my Miata) would really "lug" and you would feel the strange vibration. But of course when you do that in a car, you get a rich mixture for the acceleration.

Skylor's explanation of utilizing the very lean mixture makes good sense.

I should point out that the plane is surprisingly smooth and quiet when operated this way. It’s nothing like lugging the !968 Karmann Ghia I used to drive years ago.

Skylor

 

[Bcone1381]

I'm concerned that this thread may lead some folks to exceed limitations Lycoming has placed on over square operations.

These limitation can be found in the Operators Manual Performance Data graphs. (Note: Limit Manifold Pressure for Continuous Operation with arrow pointing to the graph)

I looked at many of the charts, not all. I can say with a high degree of confidence that Lycoming endorses over square operations for non-turbo engines up to about 5 inches MP per 1000 rpm. An angle valve io-360 chart looked like it might allow 5.5 inches over square.

Post #39 indicates the engine is operating about 9 inches over square. That seems extreme to me. If you operate in that arena, may you do so knowingly and aware of the risk.

 

[skylor]

I'm concerned that this thread may lead some folks to exceed limitations Lycoming has placed on over square operations.

These limitation can be found in the Operators Manual Performance Data graphs. (Note: Limit Manifold Pressure for Continuous Operation with arrow pointing to the graph)

I looked at many of the charts, not all. I can say with a high degree of confidence that Lycoming endorses over square operations for non-turbo engines up to about 5 inches MP per 1000 rpm. An angle valve io-360 chart looked like it might allow 5.5 inches over square.

Post #39 indicates the engine is operating about 9 inches over square. That seems extreme to me. If you operate in that arena, may you do so knowingly and aware of the risk.

Yep, and if you read post #46 you’ll see that I’m well aware of what the risks are. Also, you’ll note on the IO-360-A sea level and altitude performance chart it states “Best Power Mixture Unless Otherwise Noted” which is certainly not where I’m operating it at low RPM.

Also, I’m trying to figure out what “over square” really means, especially if I measure engine speed in micro-radians per fortnight!


Skylor

 

[Philz7A]

I have too much spread in EGT between the cylinders on my IO-320 to run LOP without getting GAMI injectors. The engine runs a little rough at that setting, and I'm not convinced that that would be a cost-effective upgrade at this point. As it is, I fly mostly at 60-65% power to stay out of the "red box". GAMI injectors are a ways down on my priority list.

Recently, I paid $38 for one new restrictor or jet for my RV-7a with IO-360-A1A. I had a GAMI spread between my first and last LOP cylinders of .8 GPH. Unacceptable! I took the readings (https://airflowperformance.com) using their injector nozzle tuning data sheet and instructions and will be receiving a slightly smaller jet .027” versus the original stock .028. Fairly cheap and easy way to correct this problem to get a more balanced LOP setting.