Why I No Longer Fly Lean of Peak For Now

Discussion in 'Maintenance Bay' started by Pilot Steve, Feb 19, 2020.

?

In a carbureted engine do you fly

  1. Lean of Peak

    20.9%
  2. Rich of Peak

    79.1%
  1. Pilot Steve

    Pilot Steve Pre-Flight

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    The whole lean of peak (LOP) versus rich of peak (ROP) discussion seems to be broken down into teams for a carbureted engine. Strong believers on each side.

    I was heavily in the LOP club for several years and enjoyed the reduction in fuel-guzzling and happily accepted the slightly reduced cruising speed.

    With 882 hours on my O-470 in four years, I was a maniac with the JPI in adjusting the LOP setting just so. But I've now been through two cylinders.

    Lately, I've been asking every higher time GA piot I meet and the engine shops what setting they recommend. Interestingly the feedback has been ROP is much better for your engine. One Baron pilot just told me he had 700 hours on both engines, sold the plane, and in a year the new pilot flying LOP had to pull three cylinders. The well-respected machine shop said only to fly the O-470 at least 50 ROP. I've had other similar stories as well.

    The fuel burn difference in my 182 is three gallons per hour at 100 ROP versus 50 LOP. It goes faster ROP.

    I'm sure this thread will have vigorous fans on each side of the argument. It always does. It's almost like talking politics but with pilots.

    So I'm curious what other frequent flyers have experienced LOP versus ROP and if others have now abandoned the LOP route as well based on actual experience.
     
    Last edited: Feb 19, 2020
  2. steingar

    steingar Taxi to Parking

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    I've never heard of doing LOP on a carbureted engine. Always thought that was for fuel injected engines.
     
  3. Pilot Steve

    Pilot Steve Pre-Flight

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    With a bit of carb heat, you can get the spreads pretty tight. I was a firm believer.
     
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  4. DoubleD

    DoubleD Pre-takeoff checklist

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    Agree with above, LOP usually not successful for carbureted engines due to poorer fuel distribution. Did you have a six-point engine monitor? Without one, you really don't know where the individual cylinders are, ROP/LOP.
     
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  5. DFH65

    DFH65 Pattern Altitude

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    I thought red meant don't touch?
     
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  6. Arnold

    Arnold Line Up and Wait

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    No mixture control, wouldn't know.

    BUT, whatever the manufacturer recommends would be my firs choice.
     
  7. Pilot Steve

    Pilot Steve Pre-Flight

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    You would think so but there is plenty of advice out there that LOP has no issues and is recommended. Mike Busch, the Savvy Aviator is a popular maintenance guru and stands behind LOP as the way to go. https://www.avweb.com/ownership/the-savvy-aviator-59-egt-cht-and-leaning/

    For example, he states "

    ALL THIS LOP STUFF MAY BE FINE FOR YOU FUEL-INJECTED GUYS, BUT I FLY A CESSNA 182 WITH A CARBURETED O-470 ENGINE. I’VE BEEN TOLD THAT LOP OPERATION IS A BAD IDEA FOR CARBURETED ENGINES. DO YOU AGREE?

    LOP operation is fine for any engine that can run smoothly in that configuration. However, LOP operation requires fairly even mixture distribution among the cylinders. That’s sometimes difficult to achieve in a carbureted engine, particularly the O-470 engine in a Cessna 182 (which is famous for its poor mixture distribution). There are a couple of techniques you can use to improve the mixture distribution of your carbureted engine and thereby enable the engine to be leaned more aggressively before it starts to run rough. One is to use a touch of carb heat during cruise (particularly in low OATs). The other is to avoid full-throttle operation, backing off the throttle until you can just see the slightest drop in MP. The warm induction air and the slightly cocked throttle plate both improve fuel atomization and mixture distribution in your engine, and will enable you to lean more aggressively before the engine starts running rough. You should feel quite comfortable experimenting with these techniques to see if you are able to operate LOP without creating uncomfortable engine roughness. Contrary to popular belief, you can’t hurt anything by operating LOP. If you get your engine to run smoothly LOP, I suggest you try it (and you’ll probably like it). If you can’t, then you’ll have to be content with ROP operation."
     
  8. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    for me....

    Carb'd = ROP

    Injected, and one I owned; LOP in cruise only.

    700-800hrs on cylinders is about all you are going to get on large bore Conti's. If you were to look at a bell curve, not listening to the occasional data point that someone will pipe in with.
     
  9. hindsight2020

    hindsight2020 En-Route

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    Your premise is a false dichotomy though. I won't go into the reason why, because the captive audience conti engine owner crowd on here will get uber-umbraged and I'm no longer interested in debating Stockholm Syndrome sufferers online. PM me if you want me to expand. At any rate, your mixture selection is not the reason you're pulling jugs in this instance, imo.

    As to the rest, well 50ROP coincides to peak CHT. There's literally no worse mixture setting to use if you're concerned about cylinder head longevity (and run above 65% BHP). Anything leaner or richer of that point would literally be better. :D Your monkey your circus though. G'Luck!
     
  10. hindsight2020

    hindsight2020 En-Route

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    Bingo. Hey OP, no need to PM me anymore, somebody else already spoke the quiet parts out loud. :D I'm out of this one!
     
  11. kgruber

    kgruber En-Route

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    In my Cherokee 180 I'm ROP 90% of the time, especially in cruise. I only have 180HP to begin with and at normal cruise altitudes, I'd just run out of power. Bad enough ROP.
     
  12. ktup-flyer

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    O-470s don't like LOP. Fuel distribution sucks.
     
  13. tspear

    tspear Pattern Altitude PoA Supporter

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    How does the fuel in a cylinder know to adjust how it burns if the fuel was provided by a carb or injections?

    Tim
     
  14. chemgeek

    chemgeek Cleared for Takeoff

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    For a carbureted engine without an engine monitor, "best economy" (lean until roughness occurs and enrich to just smooth out) should be slightly lean of peak overall, and "best power" (lean to max rpm) should be slightly rich of peak overall. Of course, in a carbureted engine, there might be a significant spread in local mixture in each cylinder.

    I've operated at best economy for 35 years with no obvious Ill effects re: cylinder longevity.
     
  15. Tarheelpilot

    Tarheelpilot En-Route

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    LOP in a carbureted engine is a bad idea. Mike Bushhy is a popular guy. Especially if you ask him.

    always in aviation: trust but verify. No one is infallible and we are all wrong sometimes.
     
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  16. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    I"m guessing that question was asked partly in jest, but it does underscore the misunderstanding of the problem. Of course the fuel doesn't know. The problem in a carburetted engine is that each cylinder gets a varying amount of fuel, so while one cylinder may be way lean of peak, another cylinder may still be way rich of peak. And by time you get that last cylinder to peak, the first cylinder is now going to be so lean as to be fuel starved. The same thing happens to some extent in many injected engines. That is why GAMI came out with their balanced injectors. But even they are not perfectly balanced.

    But as has been said, LOP or ROP is not usually why those cylinders fail.
     
  17. Tantalum

    Tantalum Final Approach

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    Yes. To what everyone else said!

    LOP in a carb'd engine = NO. The reasons should be obvious
    LOP in a healthy fuel injected engine = cruise

    Campfires / diesels / turbines / lanterns / most modern car engines, all burn LOP. It's not a magical dark science
     
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  18. Tantalum

    Tantalum Final Approach

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    People are frighteningly clueless when it comes to how an engine works.

    Lean <> hot
     
  19. brcase

    brcase Pattern Altitude

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    I suspect this is the case and the non-scientific evidence I have seen seems to support it.
    The 135 operator we had a the field for a number of years flew a couple 182's almost daily. Seemed like they regularly replaced cylinders in the 700-800 hour range on the O-470's. These were primarily flown by the same 2 or 3 pilots doing about 250 mile cross country flights daily., I know they flew the engines to TBO a number of times, but the cylinders rarely if ever made it to TBO.
    I once saw an analysis of trade-a-plane ads, could do the same with barnstormers now, looking at the distribution of top end times on specific aircraft and engines. I recall they looked specifically at C-210 engines, but the same could be done for any model with a significant number of ads. The result was essentially that it appeared very few C-210 cylinders were making it beyond the 7-800 hour mark. This was quite some time ago.

    I rarely fly airplanes that have the engine monitor and fuel distribution to run well LOP. But for the experts that claim LOP is not good for the engine I am interested in specifically why they think that. The data seems to indicate the LOP runs cooler and at lower cylinder pressures than equivalent ROP settings. Do they have data that contradicts that? Is there something else about LOP that they think is bad for the cylinder?

    Brian
    CFIIG/ASEL
     
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  20. brcase

    brcase Pattern Altitude

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    For the OP this is a great one or maybe six data point test. You have been running LOP with an engine monitor. You recently replaced 2 cylinders. So now run it ROP, I suspect as long as you don't abuse it (high CHT's) and run book power settings, You will still be replacing one or more of the remaining cylinders every couple hundred hours now until they are all replaced or your you decided to do a whole top end. let us know what really happens.

    But that is pretty much an uneducated guess, others probably know way better than me.
     
  21. tspear

    tspear Pattern Altitude PoA Supporter

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    Partly in jest, partly seriously. mostly to make the point. LOP/ROP does not matter, the operator does. With carb engines; you often have very uneven fuel flows; as such you need to be more concerned running in the red box period. LOP/ROP does not matter.

    Tim
     
  22. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    Yep. That's pretty much what I said. I"m not sure what you are arguing about. With a carburetted engine, if you try to run LOP, you will most likely have some cylinders lean, some rich, and some "red". ergo, don't try LOP with carburetted engines.
     
  23. Arbiter419

    Arbiter419 Cleared for Takeoff

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    We just ran a Saratoga HP at work (300 horsepower IO540 non turbo) to 2200 hours on the factory engine, no cylinder work, no nothing. Only overhauled it because it was 200 over recommended and we fly customers around in it. All of its life has been rich of peak, primarily cross country flights. One EGT probe, and one CHT probe. Maybe we just got lucky. I have to say I kind of subscribe to the opinion that if you're running these non turbo engines at altitude and making less than 75% power, you can't do a huge amount to hurt them in terms of engine management. That said, I've personally put about 500 of the most recent hours on it flying 50 ROP, because that's how the owners want it flown.

    I also spend a lot of my time flying PA46-350Ps...TIO-540-AE2A. Piper allows the things to be flown at peak, redline is 1750 TIT...which I believe is insane. I run those things 125 ROP.
     
  24. Mtns2Skies

    Mtns2Skies Super Moderator Management Council Member

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    I'm one of the occasional datapoints... 1000 hours on a 1989 Factory Reman... original cylinders, compressions are all 72-75.
    Or if we remove the massive generalizations that you speak in we can see that some engines operated properly will last a long... long time. But omigawd what will we do without our sweeping generalizations? I'd rather lose a cylinder with a rough engine and make it back to the airport than grenade the bottom end... nevermind, I'm going to stop feeding the troll.

    Anyway, back to the OP's question. I do what it takes to keep my EGT's below 1450 and my CHT's below 380. In the winter that means running carb heat to even out the mixture distribution, but in temperatures 50+ everything is as happy as can be ROP.
     
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  25. Grum.Man

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    Curious why you had to replace the cylinder? Leaking valve? Tapered barrel? Failed Ring or crack in cylinder? I don't buy that one manufacturer has a superior engine and I have a hard time believing that LOP or ROP makes a big difference as long as the temperatures and pressures are under control. If I were picking sides I am in the Continental camp. They may have had some production issues in the past but their support, manuals, charts and general engine design is better from my engineering perspective. They seem to have a better lubrication design as well and IMHO are easier to work on. Plus I prefer gear driven accessories to belt driven.
     
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  26. Aviator305

    Aviator305 Pre-Flight

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    It might not be random. I would be more inclined to buy a plane with a mid-time 1989 reman than a new or remanufactured Continental. If anyone is interested, go to Beechtalk and it won’t be hard to find evidence of quality control and manufacturing issues. I suspect the OP will likely need to go through more cylinders regardless of ROP versus LOP operation.
     
  27. donjohnston

    donjohnston Line Up and Wait

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    I never could get the spread on my old O540 to the point where I could run LOP. I do it all the time on the IO550 now though.
     
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  28. Aviator305

    Aviator305 Pre-Flight

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    I fly behind a Lycoming O-540-J3A5D. When flying at “55%” or “65%” power settings, I lean until a stumble and then enrich until smooth operation. Correlation with my engine monitor shows that this puts 5 out 6 cylinders lean of peak and my richest cylinder #6 near or at peak. When flying at 75% power, I lean to a 125 degree ROP fuel flow. CHTs are in the 350’s across the board except #2 when running ROP 75% which knocks on the door of 380ºF (there’s a modification for my particular aircraft that I’ll ask my mechanic to perform to take care of that). In short, it’s possible to run LOP or close to it with a carbureted engine, but the real question is can you do this with all carbureted engines and the answer to that is “no.” The Continental O-470’s induction system is notorious.
     
  29. Pilot Steve

    Pilot Steve Pre-Flight

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    Exhaust valve in one and exhaust valve guides in another.
     
  30. Grum.Man

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    What's done is done but usually those are easily fixed without having to replace the whole cylinder. Shoot the guide could even be fixed without removing the cylinder assuming it was sticking and not cracked or some other catastrophic problem.
     
  31. Pilot Steve

    Pilot Steve Pre-Flight

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    The first cylinder was replaced (which it probably didn't need to be) and the shattered valve guide cylinder was reconditioned and not replaced.
     
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  32. flyingbrit

    flyingbrit Pre-takeoff checklist

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    No, modern car engines with electronic fuel injection strive to maintain stoichiometric A/F ratio. This is the same as peak EGT. It allows a modern 3-way catalyst to work. ROP and the CO/HC goes up. LOP and the NOx goes up.
     
  33. Arnold

    Arnold Line Up and Wait

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    Hmmm. I wonder if modern day mechanics are as good at saving the owner money as folks with a couple of decades or more of experience. I can easily see a mechanic finding it easier and just as profitable to replace a cylinder rather than repair a valve. This is a thought not an assertion.
     
  34. Grum.Man

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    Outside looking in, it makes no sense for a mechanic to repair a cylinder in this litigious society. When shop rates were cheap and people didn't have a lawyer on retainer it made sense. For liability reasons most mechanics will just tell you to buy a cylinder and they will put it on.
     
  35. Arnold

    Arnold Line Up and Wait

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    Sigh . . . makes sense.
     
  36. Pilot Steve

    Pilot Steve Pre-Flight

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    You raise an excellent point. It seems the mechanic artists in GA are dwindling. Gone are the days of the "guy" at the field you could count on. My modern reality is often having an issue that I can't fly to fix and having to use a shop on the field that charges a surcharge for customer supplied parts and looks to replace rather than repair.

    The replaced cylinder was $1,132 but had some added labor to get it all ready for assembly. My reconditioned cylinder was $900 at http://www.hhtriad.com/engine
     
  37. Tantalum

    Tantalum Final Approach

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    NOx only forms in high temps, this is that fallacy that "lean = hot" - if you go outside the 14.7:1 then temps start cooling, this is true whether LOP or ROP, you either have unburned vaporized gas (ROP), or too much air (LOP)

    Mixture may also vary by car, I have a few extra gauges on the BMW and Toyota, and while the Yota (FJ Cruiser) hangs out around 12-15.1 (notice, sometimes on the lean side of 14.7), I have noticed that during highway cruise settings the bimmer will go up towards 15-16..

    The video I posted above from the engineer talks about NOx and true LOP vs a mixture that is still technically "rich" but close to peak
     
  38. Grum.Man

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    Oh dear god not triad.... Keep your receipt is all I am saying on that.
     
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  39. Grum.Man

    Grum.Man En-Route

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    All modern cars will run slightly lean under light loads and go slightly fat under heavy loads. The way tuners achieve their claims is by going even leaner on the light loads and adding timing under heavy loads and even more fuel. Prior to wide band all cars were tuned a little rich.
     
  40. Arnold

    Arnold Line Up and Wait

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    Together that is 12.5% of the value of the L8.