Caution - Religious discussion, click here only if you can handle this topic.

[Half Fast]

I heard praying works pretty well!

"Leaning, leaning,
safe and secure from all alarms;
leaning, leaning,
leaning on the everlasting arms."

 

[Llewtrah381]

I was able to find a couple of different indexes at AvWeb that appear to have the right links to the articles:

Pelican's Perch - AVweb

John Deakin

avweb.com

"Pelican's Perch" Index

Pelican's Perch #80: Gear-Up Landing In A 747? - (Articles - Nov. 21, 2004)

avweb.com

At least, I didn't get any broken links this time.

This may help:
Link
It summarizes many of his points plus it includes some commentary on the RV forum 15 years ago.
Please remember I'm flying a N/A O-360 and he (Deakin) was flying a Bonanza with a Continental. Once again, I note the manufacturers have two different "never exceed" CHTs.

 

[Caractacus]

Assuming you’re not going high enough for full rich to cause problems. Does Lycoming documentation really indicate that climbing to 10,000 feet or higher should be done full rich?

What I found doesn’t seem to…

I haven't read further, so I might be late to the discussion, but I have a distinct memory of taking off from Winslow, AZ when I was flying my Mooney home for the first time (around 4000' MSL) full rich and having to lean by the time I reached about 9000' because the engine literally started to sputter. So...I am pretty religious about leaning in the climb taking off from my home field in Colorado. I definitely should have known better than to leave it full rich for as long as I did, but lesson learned.

My C is carbureted so I don't even worry about LOP.

 

[Llewtrah381]

You run the CHTs to 435, expect to do a top end overhaul at least once before TBO. That is the common expectation.

Serious question: what, generally, is the reason for the top overhauls for these? Fried exhaust valves? Bad valve guides? Ring issues?

I’m REALLY trying to get my head around what does and doesn’t hurt my N/A, carbureted O-360 and, honestly, this thread at least feels like it’s slanted to injected Continentals and missing the point that not all engines are the same. (Add: my sense is people are extrapolating data largely obtained on/for injected Continentals to other engines without realizing the differences)

Thanks

 

[kyleb]

Serious question: what, generally, is the reason for the top overhauls for these? Fried exhaust valves? Bad valve guides? Ring issues?

I’m REALLY trying to get my head around what does and doesn’t hurt my N/A, carbureted O-360 and, honestly, this thread at least feels like it’s slanted to injected Continentals and missing the point that not all engines are the same. (Add: my sense is people are extrapolating data largely obtained on/for injected Continentals to other engines without realizing the differences)

Thanks

Deakin's stuff and Bush's stuff is substantially driven by their experience with Continentals. Listen to Deakin's principles and Lycoming's CHT recommendations, and I think you'll be OK. I can tell you that my carb'd 4 cylinder Lyc won't run LOP, but the fuel injected 540 on the RV-10 will (but not particularly well)...

 

[Ed Haywood]

the best you do without engine instrumentation is to fly at 65% power or less. Then lean any way you want, and you'll be OK.

Or put a CHT gauge on the hottest cylinder.

 

[flyingcheesehead]

Please remember I'm flying a N/A O-360 and he (Deakin) was flying a Bonanza with a Continental. Once again, I note the manufacturers have two different "never exceed" CHTs.

They may build their cylinders out of slightly different alloys... Or their engineers may have different preferences when it comes to tolerances.

I’m REALLY trying to get my head around what does and doesn’t hurt my N/A, carbureted O-360 and, honestly, this thread at least feels like it’s slanted to injected Continentals and missing the point that not all engines are the same. (Add: my sense is people are extrapolating data largely obtained on/for injected Continentals to other engines without realizing the differences)

What are the differences that would matter?

Sure, they're different, but not in huge ways. The fuel injection is slightly different (Lyc has no return line to the fuel tanks, for example) and that sort of thing, but they're all flat engines with separate cylinders, magneto ignition, similar compression ratios, carb or continuous flow fuel injection, etc... It's not like the physics or operating principles are hugely different.

The mixture of fuel and air and how they burn is the same no matter what brand of engine you have. Turbo vs. NA, 25º vs 20º BTDC ignition timing, etc are much bigger differences than Conti vs Lyc.

The really good news for you is that a normally aspirated O-360 can take a helluva lot of abuse and still run for a very long time. I sold our club's Archer with well north of 3,000 hours since overhaul and it's probably still ticking.

 

[Martin Pauly]

Or put a CHT gauge on the hottest cylinder.

Yes, that keeps coming up, but it's an unsatisfactory suggestion. Because: How do you know which cylinder that is... today? Or in two months, after a tiny mechanical issue inside your engine has started to shift the fuel/air distribution between cylinders?

Answer: You have no way of knowing, at least not until the damage is done and it's too late to do something about it proactively.

Get an engine monitor, folks! There is no substitute.

- Martin

 

[Llewtrah381]

What are the differences that would matter?

A) Exactly

but, and not trying at all to be argumentative (believe it or not):

B) Fuel injection, especially with GAMIs which can better match the cylinders to each other

C) Manufacturer’s temperature limits. 460 for Continental but 500 for Lycoming. And remember: this could be due to multiple things: cylinder construction/metallurgy, valve design, and especially probe placement (given that internal temps can reach 4,000 degrees, so probe temp is a proxy), or other things.

D) Compression ratio, which I think is a biggie. In the RV thread I shared, someone noted how the O-360 is very unlikely to suffer from detonation. If that’s true (and it makes sense) and if the issue is the “medium” detonation referred to in the Pelican’s Perch articles but the O-360 isn’t realistically vulnerable to even “light” detonation, which he said could actually be beneficial, then is a temp up to 435 (65 below the red line) actually a problem?

I did look through the Pelican’s Perch stuff and I’m still of the impression the actual data was for fuel-injected (for sure; this was to develop a product for those) Continentals. I may have missed it but I’m not sure I’ve seen a graph for Lycomings in particular, which accommodates the differences in acceptable temperatures. And if there is one, was it based on the bench findings for the Lycomings or was it an extrapolation of the Continental data?

I’d really like to see what the “red box”/“red fin” looks like for the O-360 - based on hard data and not extrapolation. Especially given the comments by others about the very low risk of detonation in those, I’m suspecting it’s small or possibly insignificant. But I’d like that to be based on reality and not my guess. Given that all the work we’ve been discussing was done in support of the GAMI product, I’m not sure it’s out there. Then again, maybe it is, in association with the 100LL alternatives.

 

[Half Fast]

In the RV thread I shared, someone noted how the O-360 is very unlikely to suffer from detonation.

I’d really like to see what the “red box”/“red fin” looks like for the O-360 - based on hard data and not extrapolation.

Agreed. I'm also flying an O-360 and I would love to see some real data for it.

One other thing to consider, though, is octane. The O-360 was designed to run on 94 91, so running on 100 should provide some additional margin for detonation. I'd love to see that quantified.

Given that all the work we’ve been discussing was done in support of the GAMI product, I’m not sure it’s out there. Then again, maybe it is, in association with the 100LL alternatives.

Unfortunately, I suspect that most of the engine data taken in the development of G100UL was for higher compression engines. If a fuel will work in an engine that truly requires 100 octane, a fuel developer can have pretty good confidence that it will also work in an engine that only requires 94 91.

(Corrected error regarding O-360 octance requirement.)

 

[flyingcheesehead]

B) Fuel injection, especially with GAMIs which can better match the cylinders to each other

That's merely a different way to get the fuel and air into the cylinders. It doesn't change what is happening in the cylinders.

As Deakin notes, though, it's often much more difficult to get an even distribution of fuel and air in a carbureted engine, the hint to try is to back off the throttle ever so slightly to induce some turbulent airflow which helped in at least one case. If you're carbureted and you can't run lean of peak, well, you'd still be better off paying attention to the other recommendations regarding temperature.

C) Manufacturer’s temperature limits. 460 for Continental but 500 for Lycoming. And remember: this could be due to multiple things: cylinder construction/metallurgy, valve design, and especially probe placement (given that internal temps can reach 4,000 degrees, so probe temp is a proxy), or other things.

But again, those are *limits*. And I'll say it again since Ted hasn't popped in here: Limits are not goals. I don't care if it's 460 or 500, I'm not going over 400.

D) Compression ratio, which I think is a biggie.

I don't think there's a big difference between Conti and Lyc here, I think most GA NA engines run at about 8.5:1 and turbocharged ones around 7:1.

I’d really like to see what the “red box”/“red fin” looks like for the O-360 - based on hard data and not extrapolation. Especially given the comments by others about the very low risk of detonation in those, I’m suspecting it’s small or possibly insignificant. But I’d like that to be based on reality and not my guess. Given that all the work we’ve been discussing was done in support of the GAMI product, I’m not sure it’s out there. Then again, maybe it is, in association with the 100LL alternatives.

Where the red box is may be slightly different. Who knows, maybe the O-360 doesn't even really have one. You're still going to have better engine longevity the farther you stay from the limits.

 

[Llewtrah381]

Where the red box is may be slightly different. Who knows, maybe the O-360 doesn't even really have one.

Exactly. I’d like to know, so I’m not constraining myself based on the limits of a significantly different engine.

You're still going to have better engine longevity the farther you stay from the limits.

Please substantiate that claim. I’m not disagreeing - I’m saying I haven’t seen substantiation.

And I’d be cautious treating LOP too cavalierly: some valid points are raised here:

https://data.ntsb.gov/Docket/Document/docBLOB?ID=40317635&FileExtension=.PDF&FileName=Lycoming%20Leaning%20Instructions-Master.PDF

 

[455 Bravo Uniform]

Oil temperature is another interesting parameter to monitor ROP and LOP, as well as percent HP. I think it can be an indicator of cylinder pressure to some extent. Airspeed and angle of attack are cooling variables that make this a bit messy.

 

[MauleSkinner]

And I’d be cautious treating LOP too cavalierly: some valid points are raised here:

https://data.ntsb.gov/Docket/Docume...Name=Lycoming Leaning Instructions-Master.PDF

At least be more cautious than 98% of pilots who operate LOP as Lycoming claims.

 

[Jim K]

Don't get hung up on the engine, or the specific numbers. The point is that cylinder pressure peaks just before egt does. That's true of every engine regardless of make/ model. Getting 100 degrees ROP or -50 LOP gets you out of the "red box/ fin" which is a shorthand for the most stressful operating regime. Detonation can occur here, which will quickly destroy an engine

Another way to to reduce power, which obviously reduces cylinder pressure. That's actually how I operate my engine: 65% power and very close to peak egt. That's where you'll find yourself using the old "lean to roughness and screw it back in a couple turns". Best not to run WOT below about 5000' at that setting. If you don't have an engine monitor, that's about the best you can do.

Where different engines come into it is that some are more tolerant of abuse. An 0-360 is already pretty low compression (lower cylinder pressure) and understressed, so they're very hard to hurt. Detonation is almost impossible with 100 octane fuel. Injected engines can be balanced to run very well LOP (gamijectors), carbs mostly can't.

Lycoming saying running lop is bad is silly. An engine is an engine. It either works or it doesn't. It works if done correctly. You're simply limiting engine HP by limiting fuel rather than air. That's how all modern automotive engines run, btw.

 

[Llewtrah381]

Oil temperature is another interesting parameter to monitor ROP and LOP, as well as percent HP. I think it can be an indicator of cylinder pressure to some extent. Airspeed and angle of attack are cooling variables that make this a bit messy.

LOL - agree. But have been toying with throwing into the “if cool is good, cooler must be better” comments “…then do you work to keep your oil temp below 160?”

Pretty much all of us could say why that’s not a good idea - but I haven’t seen anyone say exactly why 360 is better than 380.

 

[Llewtrah381]

That's how all modern automotive engines run, btw.

Except they use computers monitoring each cylinder’s flow and spark and with knock detectors. They don’t rely on a ham-fisted weekend warrior trying to see how far they can pull back the mixture knob

 

[OneCharlieTango]

Oil temperature is another interesting parameter to monitor ROP and LOP, as well as percent HP. I think it can be an indicator of cylinder pressure to some extent. Airspeed and angle of attack are cooling variables that make this a bit messy.

Depends on where you're getting your data for HP. Engine analyzers are notoriously inaccurate in estimating that when ROP and worthless when LOP, though the very newest might be better. For ROP, use the performance charts. For LOP (with an 8.5:1 compression ratio), HP= 14.9 x FF. divide that by max continuous for percent. So, in my IO-520 running 12 gph LOP, % power = (14.9 x 12)/285 =0.627.

It's worth emphasizing: If you're at, say, 65% and ROP, when you do the Big Mixture Pull to go LOP, you're no longer at 65%.

As for oil temp, mine is always lower when LOP.

 

[flyingcheesehead]

Exactly. I’d like to know, so I’m not constraining myself based on the limits of a significantly different engine.

Well, go ahead and beat up your engine. I will tell you that I know it's possible to crack all four cylinders in one year on an O-360. As you said, "the data" probably doesn't exist for an O-360, so either you can find it by running your engine to failure, or you can be okay with going maybe 5 knots under max speed and having your engine last way longer.

Please substantiate that claim. I’m not disagreeing - I’m saying I haven’t seen substantiation.

That one should be pretty obvious. If you hammer something lightly, you can hit it as many times as you want without causing damage. Hammer it hard and you can damage it in one stroke. That's pretty much what we're talking about here.

LOL - agree. But have been toying with throwing into the “if cool is good, cooler must be better” comments “…then do you work to keep your oil temp below 160?”

Sigh... No, I'm not trying to boil water out of my cylinder walls.

Depends on where you're getting your data for HP. Engine analyzers are notoriously inaccurate in estimating that when ROP and worthless when LOP, though the very newest might be better.

This! One that's OK is my Insight G3, it gives two different percentages, one for ROP and one for LOP, and you just use whichever one applies at that moment.

For ROP, use the performance charts.

You can also get a pretty good approximation using (Max HP) * (Actual RPM/Max RPM) * (Actual MP/29.92) because power is limited by mass airflow when you're ROP.

 

[Llewtrah381]

I will tell you that I know it's possible to crack all four cylinders in one year on an O-360.

Prolly from running LOP

This religious thread has gone on longer than I thought the mods would allow…

 

[Bill]

Eh, a good rehash every few years is good for the newbies.

 

[flyingcheesehead]

Prolly from running LOP

Nah, that thing didn't have an engine monitor. Prolly ran full rich half the time.

 

[Narwhal]

I would just like to know if it’s possible to get detonation at low CHT - let’s say it’s -40F outside at sea level and you hammer an IO-360 with a Vx climb to 14,000 ft at 50 ROP. CHT never breaks 380F on any cylinder. Could there be damage?

The only damage I’ve done to my engine I believe is from running it consistently too rich when it was new to me after reading red box red fin, resulting in Exhaust valve deposits that caused compression lost, luckily solvable by lapping. I now just run 65% and peak unless the CHT’s exceed 380 due to high OAT in which case I go just enough lean of peak to keep them at 380 or less.

 

[Llewtrah381]

would just like to know if it’s possible to get detonation at low CHT

My gut reaction non-engineer response is yes. CHT is a lagging indicator. Detonation can happen any time the ICP is high enough to detonate the fuel and can happen very quickly, from what I understand. Even outside of extremely cold situations, it seems like one could rapidly increase ICP through several methods and get detonation long before the CHT catches up with the situation. A full-power climb while improperly leaned seems like one example. A turbo could probably get into situations pretty quickly, I’m sure.

Your comments about running too rich are spot on. I personally want to know which does more long term harm: running below the “maximum service life” temp (435 for a Lycoming for high performance) or running excessively rich in order to keep a cylinder at 380.

 

[Rick A]

I personally want to know which does more long term harm: running below the “maximum service life” temp (435 for a Lycoming for high performance) or running excessively rich in order to keep a cylinder at 380.

Good question. Maybe split the difference and step-climb?

 

[iamtheari]

Something to consider is that metal gets weaker as it gets hotter. I seem to recall a graph of strength over temperature for the alloys used in aircraft engine cylinders but I don’t have that in front of me. If memory serves, there was something of a cliff effect at the redline CHT numbers. But it wasn’t flat before that point.

Vic Syracuse wrote this article, which discusses the temperature recommendations for Lycoming and Continental engines: https://inspire.eaa.org/2024/03/14/understanding-chts-and-egts/

One thing he says is that aluminum is half-strength around 400F. So if you do get detonation, it stands to reason that you’ll do more damage if the detonation happens inside a 460F cylinder versus one that’s only 360F.

I try to keep my CHTs below 380 as much as possible and start thinking about doing something different if they hit 400. That’s not always easy, and sometimes impossible during the initial climb. But if limits aren’t goals, then I at least want to set some goals for myself.

 

[Ed Haywood]

One thing he says is that aluminum is half-strength around 400F. So if you do get detonation, it stands to reason that you’ll do more damage if the detonation happens inside a 460F cylinder versus one that’s only 360F.

Here's a good article by the Engine Pope that explains why 360 is not a good target:

Hot-heads

For decades, I’ve been preaching that the two keys to piston aircraft engine longevity are avoiding extended periods of disuse and managing cylinder head temperatures.

www.aopa.org

 

[iamtheari]

Here's a good article by the Engine Pope that explains why 360 is not a good target:

Hot-heads

For decades, I’ve been preaching that the two keys to piston aircraft engine longevity are avoiding extended periods of disuse and managing cylinder head temperatures.

www.aopa.org

My read from that article is that Busch’s green arc for CHT is 350-400 for Lycoming and 330-380 for Continental.

 

[Half Fast]

My read from that article is that Busch’s green arc for CHT is 350-400 for Lycoming and 330-380 for Continental.

I wonder what it is for Superior cylinders.

 

[Ed Haywood]

My read from that article is that Busch’s green arc for CHT is 350-400 for Lycoming and 330-380 for Continental.

"I explained that 370 degrees F was not a realistic CHT limit for his engine, and in fact was a bit cooler than optimal."

...

"Personally, I like to leave myself a little cushion, so I’m inclined to set CHT targets of about 380 degrees F for Continentals and 400 degrees F for Lycomings. These aren’t not-to-exceed values, they’re just comfortable targets. A good way to think of them is to imagine a CHT gauge with a green arc that tops out at these targets, followed by a yellow arc that extends 20 degrees F higher and terminates with a redline."

 

[Llewtrah381]

"I explained that 370 degrees F was not a realistic CHT limit for his engine, and in fact was a bit cooler than optimal."

...

"Personally, I like to leave myself a little cushion, so I’m inclined to set CHT targets of about 380 degrees F for Continentals and 400 degrees F for Lycomings. These aren’t not-to-exceed values, they’re just comfortable targets. A good way to think of them is to imagine a CHT gauge with a green arc that tops out at these targets, followed by a yellow arc that extends 20 degrees F higher and terminates with a redline."

Yeah - good article and I don’t disagree with his language here about “comfortable targets”. How that got translated into I’m gonna ruin my engine by running it at over 400 is a head-scratcher - but probably relates to the thread title.

I do wish there was a deeper explanation around the red box/red fin re WHY they’re “abusive” zones. If it’s because of the risk of detonation, so be it. Then one needs to distinguish between low and high compression engines, turbo, etc. and the relative size of the boxes for different engines. Plus, if that’s true, it would seem wise to point out going LOP and cooling the CHTs gives a false sense of security when needing to go to high power for a climb, etc and pushing in the throttle and mixture: seems like it could go deep into the purple box on the transition if not done cautiously. That could give detonation despite a cool CHT.

I have the sense people believe high CHT per se is causative and not just a correlation and overlook that it’s a lagging indicator of what’s really of interest/concern (ICT).

 

[Llewtrah381]

I wonder what it is for Superior cylinders.

My sense is, since there PMA’d, the temps are the same for the type of engine they’re going on. I just had them put on mine last fall and that’s what I understood.

 

[Ed Haywood]

Here's a good article from Lycoming on detonation.

https://www.lycoming.com/tips/detonation

IMO it gives some insight into why they are opposed to LOP. Money quotes:

for a pilot the number one cause of detonation is excessive leaning at high power settings.

Lycoming engines meet or exceed the FAA guidance for detonation margin. Therefore, if an engine is maintained and operated in accordance with our published guidance, the engine should never experience detonation.

 

[Hang 4]

Quoting @Ed Haywood quoting Lycoming

"for a pilot the number one cause of detonation is excessive leaning at high power settings."

Not sure any of the LOP faithful would disagree with that statement. LOP at 65% power should be fine.

 

[Ed Haywood]

That could give detonation despite a cool CHT.

I have the sense people believe high CHT per se is causative and not just a correlation and overlook that it’s a lagging indicator of what’s really of interest/concern (ICT).

Absent mechanical defects such as ignition timing, high CHT is causative.

 

[Ed Haywood]

Not sure any of the LOP faithful would disagree with that statement. LOP at 65% power should be fine.

Per Lycoming, anything is fine at 65%.

 

[MauleSkinner]

Per Lycoming, anything is fine at 65%.

And yet they’re still opposed to educated LOP.

 

[Martin Pauly]

Quoting @Ed Haywood quoting Lycoming

"for a pilot the number one cause of detonation is excessive leaning at high power settings."

There is absolutely no problem with running LOP at higher power settings, but one must be lean enough. Think 100 deg F LOP or so.

Where people get into trouble is they want to try LOP, but they also want to be careful, so they lean less aggressively than required to stay outside of the red box.

Not every engine will run that far LOP smoothly. If yours doesn’t, fly ROP at higher power settings.

- Martin

 

[Llewtrah381]

Absent mechanical defects such as ignition timing, high CHT is causative.

OK - please remember the constraints of communicating online and not in person.

Serious question: is there a CHT (alone) below the 500 degree limit for my Lycoming O-360 which will cause it to have detonation on 100LL, even at the riskiest mixture?

 

[455 Bravo Uniform]

You’re more likely to get detonation in a hotter combustion chamber.

As to cylinder damage, wear, or catastrophic failure, I think heat is not good. But detonation in most engine applications (cars/racing) causes rod bearing failures, not usually top end except for maybe cracked rings, which then eats the cylinders, not the cylinders just failing due to heat.

The ends of the rod bearing pinch inward when detonation hammers it and then they wear or even grab the crank. The wear will eventually hemorrhage oil and cause low oil pressure and oil heat that will end badly. If the bearing grabs the crank, it’s game over.

My default way of thinking which may not 100% translate to air cooled jugs.