LOP on carburated engines

J

jtheune

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John T
I know that for the most part you cannot run LOP on a carb because of uneven fuel mixtures but I have read that some engines will run LOP even with a carb if the mixtures are even. So my question is this: If you have a all cylinder engine monitor and can see your CHTs how even must they be when running ROP before you should try running LOP? Is a 10 degree spread ok? 20 degrees? Anyone have any info on this?
 
Funny thing when we had no gauge, we would pull the mixture until we felt a vib, then richen it until we didn't feel a vib. Which insured we had at least one cylinder LOP, but now We have a gauge and can't do that ?

:confused:
 
The old lean till rough then rich till smooth will get you the best economy on the gauge every time. Use an engine monitor and it will be no better.
 
Ted DuPuis said:
The old lean till rough then rich till smooth will get you the best economy on the gauge every time. Use an engine monitor and it will be no better.
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No,,,,,,,,,, you must have a gauge and proof written on the internet chat page to get that every time.
 
Ted DuPuis said:
The old lean till rough then rich till smooth will get you the best economy on the gauge every time. Use an engine monitor and it will be no better.
Click to expand...

And the idea with well balanced air/fuel flow is that "rough point" is leaner than un-balanced, right?

The folks at Jabiru USA have found that a splitter/divider like device after the carb really helps to even out cyl temps. They have been playing around with this a bit and seem to have hit on a nice solution. They used to / still advise that slightly tilting/twisting the bing carb* can help with some balancing, but this splitter is great. They or someone is going to make them, but they've posted pics of it and it looks like anyone could make it.

*toward or away from the hot side, I forget which.

This is probably similar to how slightly closing the throttle can help with balance on "standard" AC engines.
 
jhausch said:
And the idea with well balanced air/fuel flow is that "rough point" is leaner than un-balanced, right?
Click to expand...
Bingo.

The folks at Jabiru USA have found that a splitter/divider like device after the carb really helps to even out cyl temps. They have been playing around with this a bit and seem to have hit on a nice solution. They used to / still advise that slightly tilting/twisting the bing carb* can help with some balancing, but this splitter is great. They or someone is going to make them, but they've posted pics of it and it looks like anyone could make it.
Click to expand...

Back in the olden days when cars still had that kind of thing. A lot of time and effort was spent on bumps and bits in the manifold under the carb to get fuel to go to the various cylinders reasonably equally. Ford even put a "diving board" (which cost money) over the inlet of their throttle body injection systems to do the same thing for a while.
 
Tom-D said:
Funny thing when we had no gauge, we would pull the mixture until we felt a vib, then richen it until we didn't feel a vib. Which insured we had at least one cylinder LOP, but now We have a gauge and can't do that ?

:confused:
Click to expand...

Ted DuPuis said:
The old lean till rough then rich till smooth will get you the best economy on the gauge every time. Use an engine monitor and it will be no better.
Click to expand...


Very true, HOWEVER, it is possible to get yourself into trouble when running high power settings and leaning that way because you don't know where each of your cylinders are with regards to EGT. The monitor isn't about getting it leaned out in this situation, it's about telling you whether everything is in a safe parameter.

Lack of information is what leads to burned up cylinders which is what led to the OWT of "Don't run LOP, You'll destroy your engine!!!" It wasn't the lean cylinders that would get destroyed, it was the rich ones.
 
Henning said:
it's about telling you whether everything is in a safe parameter.
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When running below 65% power any mixture setting is with in safe parameter.

the only warnings the 2 major engine manufacturers give are for settings above 65%.
 
Henning said:
Very true, HOWEVER, it is possible to get yourself into trouble when running high power settings and leaning that way because you don't know where each of your cylinders are with regards to EGT. The monitor isn't about getting it leaned out in this situation, it's about telling you whether everything is in a safe parameter.

Lack of information is what leads to burned up cylinders which is what led to the OWT of "Don't run LOP, You'll destroy your engine!!!" It wasn't the lean cylinders that would get destroyed, it was the rich ones.
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If you lose about 3% of your indicated airspeed going from best power to LOP without roughness, your engine is balanced well enough to run LOP without worrying about one or more cylinders running too rich.
 
Tom-D said:
When running below 65% power any mixture setting is with in safe parameter.

the only warnings the 2 major engine manufacturers give are for settings above 65%.
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Yep, but lots of people aren't running below 65% power.
 
gismo said:
If you lose about 3% of your indicated airspeed going from best power to LOP without roughness, your engine is balanced well enough to run LOP without worrying about one or more cylinders running too rich.
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That is not true. Get a spare injector nozzle and drill it out a bit and try it. You'll find that you can be properly LOP and smooth on 5 cylinders and be ready to cook #6. I realize that this isn't a real situation but it simulates what happens if you have multiple nozzle screens clogging and one clear.
 
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Henning said:
That is not true. Get a spare injector nozzle and drill it out a bit and try it. You'll find that you can be properly LOP and smooth on 5 cylinders and be ready to cook #6. I realize that this isn't a real situation but it simulates what happens if you have multiple nozzle screens clogging and one clear.
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The OP's question/concern/inquiry revolved around engines with carburetors.
 
Henning said:
That is not true. Get a spare injector nozzle and drill it out a bit and try it. You'll find that you can be properly LOP and smooth on 5 cylinders and be ready to cook #6. I realize that this isn't a real situation but it simulates what happens if you have multiple nozzle screens clogging and one clear.
Click to expand...
How in the world would you end up with one clear and 5 clogged? As long as no more than half are restricted unless all are, this technique works.

But in any case my original post was about carbureted engines which aren't likely to suffer from any restricted injectors.
 
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Henning said:
Very true, HOWEVER, it is possible to get yourself into trouble when running high power settings and leaning that way because you don't know where each of your cylinders are with regards to EGT. The monitor isn't about getting it leaned out in this situation, it's about telling you whether everything is in a safe parameter.
Click to expand...

What carbureted engines do you know of that have detonation concerns (excluding old radials or supercharged units)? Or are you referring to CHT, which you won't know about without a full-on engine monitor?
 
Ummm lots of us run below 65% for just tooling around - at least I do, which is 'lots' to me....
Lean it till it shakes (slightly) - and leave it there...
Been doing this for over 50 years... My engines make TBO and then some... My current engines are on their second set of cylinders and the bottoms are still perfect (as far as we can tell)...
The left engine is <10 hours on the new cylinders so the flight to Port Clinton Saturday was still the full-rich-balls-to-the-wall variety, for seating rings...
Kinda fun flying well up in the yellow - really expensive at the gas pump afterwards at $5.45 a gallon...
WHile at the cottage we went to the boat show at the yacht club (CIC) - glad I'm not buying fuel for those barges - though I did take a shine to the 55 footer...

denny-o
 
Ted DuPuis said:
What carbureted engines do you know of that have detonation concerns (excluding old radials or supercharged units)? Or are you referring to CHT, which you won't know about without a full-on engine monitor?
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All of them.
 
I run LOP with my O-320 carburated engine all the time. I have an Insight GEM 610 with digital EGT/CHT temp readouts. I set it to display CHT#4 and keep the temp at or below 400 on climbout. At cruise alt, I lean further and see temps on #3 and #4 in the 365-375 range, with #1 and #2 being 10o cooler, which is normal for front cyl's. My plugs always look nice and clean with a light brown color... no fouling. I do sacrifice a little power, but the economy at this setting is fantastic. I flew 800+ mi to Las Vegas and back to Tucson last week and averaged 6.5gph for the trip! I was running 2350-2400 rpms at cruise.... not full throttle. CHT's were all under 370 and fuel flow was showing 6.3-6.5gph. Engine was smooth and oil temp stayed right on 180. You're not going to hurt anything running like that. The lean till rough and back off till smooth method, effectively gets you very close to this type setting, so anyone using that leaning method without instrumentation is likely flying LOP, whether they know it or not.... I didn't know it until I added the instrumentation. The fuel flow and EGT/CHT instruments really help me dial it in without guessing.... well worth the money to me.
 
Henning said:
You can always get into detonation.
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Have you had detonation issues on parallel valve O-320s and O-360s when run on 100LL?
 
Tom-D said:
Not by mixtures, and that is what this thread is about, running LOP.
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If everything remains perfect on an engine, we wouldn't need mechanics. Analyzers let you know when things are no longer right. Points cams wear, points followers wear, points slip... all of which have an effect on timing. Then there is also the ability to affect the thetaP timing with the blue lever. Any gasoline burning recip engine is just a small margin from detonation when properly tuned and making efficient power. As I said, they aren't about knowing how to lean, analyzers are for knowing when things are starting to go wrong before they get destructive.
 
Henning said:
If everything remains perfect on an engine, we wouldn't need mechanics. Analyzers let you know when things are no longer right. Points cams wear, points followers wear, points slip... all of which have an effect on timing. Then there is also the ability to affect the thetaP timing with the blue lever. Any gasoline burning recip engine is just a small margin from detonation when properly tuned and making efficient power. As I said, they aren't about knowing how to lean, analyzers are for knowing when things are starting to go wrong before they get destructive.
Click to expand...

All that has nothing to do with getting any engine to detonate by changing mixture.

You can do a great deal of damage by running too hot, but you can't harm your engine from detonation by reducing or adding fuel.
 
Henning said:
If everything remains perfect on an engine, we wouldn't need mechanics. Analyzers let you know when things are no longer right. Points cams wear, points followers wear, points slip... all of which have an effect on timing. Then there is also the ability to affect the thetaP timing with the blue lever. Any gasoline burning recip engine is just a small margin from detonation when properly tuned and making efficient power. As I said, they aren't about knowing how to lean, analyzers are for knowing when things are starting to go wrong before they get destructive.
Click to expand...

I would suggest that you read the regulations that go into aircraft engine certification and see what margins are required by the FAA at a minimum, and the operating conditions under which these things are tested.

Then I would suggest that you actually go out and do some experimentation to see just how much of an impact factors such as CHT, IAT, Oil Temp, mixture, and RPM have on detonation when lower powered engines are run on 100LL. Judging from what you say now, I believe you would be surprised at the end result. There are many factors that influence knock, which is one of the reasons why it is so misunderstood, especially from a practical application sense.

We have one fuel to work with here. That means that the high stress engines (with a high octane requirement) and the low stress engines (with a low octane requirement) are getting the same anti-knock characteristics of the fuel. The reality is that some of them need it and some of them don't.

My Ford does just fine knock wise on 87. I don't know how much it knocks, but I'm going to guess pretty close to not at all. If I put 91 in it, it will do even better. Yet if I put 87 in my twin-turbo Mitsubishi, I'll melt a piston...

Tom-D said:
All that has nothing to do with getting any engine to detonate by changing mixture.

You can do a great deal of damage by running too hot, but you can't harm your engine from detonation by reducing or adding fuel.
Click to expand...

While I understand that you're speaking to the ultimate change that causes the damage (the high temperatures and pressures), those events are frequently precipitated by a change in fuel flow. The red knob is the #1 tool that the pilot has to induce or get out of detonation on the engines we fly. I realize that the big old radials that you flew back in the day may have been different (I have no experience with them), but an R-2800 is not a 520/540/etc.
 
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