ROP vs. LOP

azpilot

azpilot

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azpilot
I hope this doesn't start a massive argument, but I don't really have much of an opinion on this topic, and I am curious what other people think.

For a GA airplane with a carbureted piston engine, and only simple EGT (i.e. just an analog dial), what are the advantages and disadvantages of running rich, and lean of peak?

The flight school where I learned to fly had me run 50 deg rich of peak, but I've recently talked to some other pilots that suggest running lean of peak can lead to prolonged engine life, reduced fuel consumption and a cleaner running engine in general.

So, any thoughts on the topic? (Ha ha ha! Why do I even ask that question... I already know the answer.)
 
You will have a hard time running LOP with a carbureted engine. The mixture distribution just isn't good enough.


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I have a Lycoming 0360 with a single CHT/EGT probe. At 65% power, I lean it until rpm drop and then come back to peak rpm. At power levels greater than 65% I richen it a bit. Thats not really lean of peak, its just leaned until as far as possible and it still runs smoothly. You can't run too lean at 65% power and below.

For true lean of peak, you need balanced fuel injection, probes on all cylinders. Then all the EGTs move together. The way you tell if you are lean of peak is to lean it and if it gets cooler, you are lean of peak.
 
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I have heard stories of guys that were able to run their carbureted engines lean of peak but they are all just that: stories.
 
I know my O470 sure as hades won't do it. It likes gas. Lots of gas.
 
Joshuajayg said:
I have heard stories of guys that were able to run their carbureted engines lean of peak but they are all just that: stories.
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Whether the stories have any validity depends on who is telling them.

People (Lindbergh, for example) have been able to get carbureted engines to run LOP, but the technique apparently involves applying manifold heat. It is even discussed in some of the old WWII P&W engine manuals.

Personally, I'm not smart enough to figure it out.
 
Fearless Tower said:
Whether the stories have any validity depends on who is telling them.

People (Lindbergh, for example) have been able to get carbureted engines to run LOP, but the technique apparently involves applying manifold heat. It is even discussed in some of the old WWII P&W engine manuals.

Personally, I'm not smart enough to figure it out.
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But I don't think your going to find anyone doing it in an O-360, O-470, O-300 etc.
 
mwagg737 said:
You will have a hard time running LOP with a carbureted engine. The mixture distribution just isn't good enough.


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This. The carburetor isn't very capable of properly distributing fuel like a FI engine can. If you're running a carb'd engine, don't worry about LOP. If you don't fully understand how it works, you'll pose high risks to the engine if not done correctly, so for now, stick to ROP.
 
You may not be able to attain "pedantic LOP" in a carbed installation, but the extra savings beyond "lean until rough" are frankly overstated. Furthermore, below 70% you're not gonna do damage to a Lyco by pulling the red knob on the CHT front, so pull that red knob.

Nothing against GAMI, but I just saved you a ton of money. You're welcome.
 
Joshuajayg said:
I have heard stories of guys that were able to run their carbureted engines lean of peak but they are all just that: stories.
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yup....hasta be....and their engines didn't come from together. :eek:

pull a lil carb heat to help with the atomization....from peak (best power)...lean till she slows 2-3kts on the AS indicator. It's approx 20-30 deg on the lean side.

btw....that's a "Power Lean"....cause one is leaning off the reduction of power output using the Air Speed as an indicator.
 
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Read anything from Mike Bush, he is the man.


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What happens with my Lycoming 0360 carbureted engine with one CHT/EGT gauge is I keep leaning and the EGT goes up until the engine starts running rough. What is happening is one or more of the other cylinders is so lean that it is missing, but cylinder that the EGT is on isn't lean of peak yet (because as I lean the EGT goes UP). The way you tell you are lean of peak is when you lean it, the EGT goes DOWN....

I could install EGT's on all the cylinders and I would know which cylinder is peaking first and going lean, but I couldn't do anything about it. (except maybe apply carb heat, but who wants to do that non-standard weird thing??). Even then it would be a crap shoot that they would all peak together (which is what you need).
 
Ive even played with the carb neat trick, and done the "cock the throttle plate" thing. The induction system on an O-470 in a 182 just isn't even enough. One cylinder will always be starved of too much fuel and missing before the others.

No big deal. It's a freaking engine designed to be air cooled sitting on top of a 1930s tractor plowing fields. I tried it, it doesn't like it, so I feed it gas and it runs just fine.

Just like the book from Cessna in 1975 says it will. Funny that.

I get it that some fuel injected engines do well with it, especially if folks fiddle with injectors to get everything even. Saves a few bucks, too. Not completely convinced it saves the engines themselves, but there's evidence both ways and it's very engine and installation specific.

I wouldn't freak out if some owner I flew with wanted to do it as SOP in their airplane as long as they're monitoring properly, and I wouldn't freak out if they said they're not a fan and ran properly leaned but on the rich side.

Up here, the DA helps. You don't have to climb very far to be at 65% power normally aspirated, WOT. Not much concern about the "red box" stuff, since you're probably not in it anytime but the cold of winter.

Turbos and superchargers, different story, of course. But Clark has all his goofy numbers for that memorized. :)
 
denverpilot said:
Turbos and superchargers, different story, of course. But Clark has all his goofy numbers for that memorized. :)
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It takes a couple flights, data dumps-n-plots, and monitoring but once ya got it, ya got it.

Keep an I on yer mechanic after that. Some of those guys think they have to fiddle with fuel trim during annual.
Clean the injectors one at a time. Never give yourself a chance to screw that up.
And final comment: use fine wire plugs if there is some slight roughness that shouldn't be there and just won't go away. Mags were in good shape and harness was replaced...finally spent the $$$$$$$ on fine wire plugs.

For the carbed guys...if ya really wanna try it then iran the mags and harness then think real hard about the plugs. Ya need everything in your favor.
 
On my carb driven engine, I lean aggressively on the ground when taxing. So aggressively that if the throttle is opened just a small amount the mixture must be richened in order for the throttle to come up. She will just fall on her face so to speak unless the mixture is richened. Then in flight I run for best performance then lean just a little until she start to miss or run rough. I then richen a little to smooth her back out. Doing this after one year of flying my plugs look like the day I took them out of the box. I also like the fine wire plug. Much harder for carbon to stick to the fine wire. IMHO.
 
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