Thoughts (Leaning Fuel Mixture and Temperatures)

[tracy]

I?m cruising my plane at 8,500? using 65% power running 166kts. The question is, is it better to lean to 8g/hr with CHT?s @ 365 deg., or run 9g/hr with CHT?s at 335 deg.? Wondering if the extra 30 deg is more wear on engine. If not, the less burn is cheaper. EGT?s are 1230 vs 1350.

[Paul 5r4]

I have nothing but an opinion and it's not an expert one at that. With the 8 gal hour settings you're still well within specs so I don't see any problem with it.

[airguy]

Why not pull it back farther and go to 7.5 gph and low CHT on the lean side?

[gmcjetpilot]

I assume you are rich of peak EGT... So how far rich of peak are you?

If you can you can run LOP, and get cooler CHT and better FF or MPG (but slightly slower speed). LOP is not practical unless you have well balanced FI where all cylinders are close to each other in EGT. Too much EGT spread will cause rough running (leanest cylinder) while others might be near or at peak EGT. You also should have full 4 channel engine monitor to run LOP.

Absolute EGT is kind of useless because it is dependent on where the probe is. Need to know how far RICH of peak you are.

The cooler the CHT the better but 365F is pretty good. I would not go over 400F. But does 30F make a difference? Yes 1 gal an hour. Engine life? That is so dependent on many factors. No answer. What is your Oil Temp?

airguy said pull it back? I think he is talking mixture. Just FYI do not "pull it back" throttle wise. You are best at FULL THROTTLE... don't partially close the throttle. You can change RPM if you have constant speed prop (within Prop RPM/MP limits), but if you want to reduce power, fly higher (if winds are favorable or no worse). Lower density air will reduce your power.


Lycoming says.... normal operation, maintain the following recommended temperature limits:

For maximum service life, maintain the following recommended limits for continuous cruise operation:
Engine power setting – 65% of rated or less.
Cylinder head temperatures – 400˚ F. or below. (that is my limit but 420F for short period is OK hot day climb, but I would not want to cruise 400F constant if able.)
Oil temperature – 165˚ F. – 220˚ F. (you don't want to run too cool, 185˚ F indicated is ideal min. That means oil in head is above 212 and boils off mosture.)

Lyc also talks of 100F RICH OF PEAK... That is pretty rich, but it sure does cool the engine down (and waste fuel)ppp... 50F rich of peak or smooth operation is good if all temps are well in the normal range. Also leaning applies only if you are below 75% power.

Great video on LOP operations.
https://www.youtube.com/watch?v=h3bATVXMHQg

[airguy]

Originally Posted by gmcjetpilot

airguy said pull it back? I think he is talking mixture. Just FYI do not "pull it back" throttle wise. You are best at FULL THROTTLE... don't partially close the throttle. You can change RPM if you have constant speed prop (within Prop RPM/MP limits), but if you want to reduce power, fly higher (if winds are favorable or no worse). Lower density air will reduce your power.


https://www.youtube.com/watch?v=h3bATVXMHQg

Yes, I meant pull the mixture back. Wide open throttle, lean of peak is where you'll find your best efficiency. Keep it lean enough to keep CHT's comfortable but rich enough to keep the power up and airspeed where you want it, all on the lean side of peak EGT.

[tracy]

Thanks guys. I do have a 4 channel engine monitoring system(d180), but I also have a carb and can only get one cyclinder lop while others are rich or at peak. The 8gl/hr setting has #1 100 deg. lean of peak. Any further and the #3 cht hits 385 deg. Also, forgot to mention that at the richer(9g/hr) setting, all cht’s Are within 10 degrees of each other, while at the leaner setting, I have a 50 deg split between #1and #3. I wonder how this ^ affects the case? I have a butterfly valve in front of oil cooler and maintain 185 degree oil temp.

[Ironflight]

Originally Posted by tracy

Thanks guys. I do have a 4 channel engine monitoring system(d180), but I also have a carb and can only get one cyclinder lop while others are rich or at peak. The 8gl/hr setting has #1 100 deg. lean of peak. Any further and the #3 cht hits 385 deg. Also, forgot to mention that at the richer(9g/hr) setting, all cht?s Are within 10 degrees of each other, while at the leaner setting, I have a 50 deg split between #1and #3. I wonder how this ^ affects the case? I have a butterfly valve in front of oil cooler and maintain 185 degree oil temp.

One little trick you can try with a carbed engine to smooth things out when LOP is to bring the throttle back ever so slightly from wide open. The theory is that this tips the throttle plate enough to create a little turbulence, which enhances mixing, and gives you more even distribution between cylinders. I?ll let folks debate the theory, but I can tell you that it seems to work on at least a couple of carbed airplanes we have.

[tracy]

Originally Posted by Ironflight

One little trick you can try with a carbed engine to smooth things out when LOP is to bring the throttle back ever so slightly from wide open. The theory is that this tips the throttle plate enough to create a little turbulence, which enhances mixing, and gives you more even distribution between cylinders. I’ll let folks debate the theory, but I can tell you that it seems to work on at least a couple of carbed airplanes we have.

I’ll try that next time I’m higher. In my cenerio, 8500’ at 65% is not wot.

[Bcone1381]

In the same spirit of slightly closing the throttle plate, you might experiment with adding some carb heat. The heat may help atomize the fuel, and introduce some turbulence prior to the carb to help or change things a bit.

[Northernliving]

I found this video on LOP/ROP one of the very best.
https://www.youtube.com/watch?v=h3bATVXMHQg&t=77s