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Carb Heat for better fuel atomization?

Agreed, but if the air is moving slower because the engine is not sucking as much then the engine will not be making as much heat. Of course you are talking about a fire breathing 520 cubic inches and the plane I was flying was a J-5 with an 0-235, a much lower heat producer.
 
An engine will produce maximum heat at full power.
Correct, i.e. the maximum temp of the exhaust gas, AND the maximum flow of the exhaust gas.

The heat passing through the heat muff will be maximum temp at full power.
Correct if you mean the heat in the exhaust gas.

The heat will transfer to the ambient air passing over the heat muff. The longer the air lingers passing over the heat muff the hotter it will get.
Correct.

Therefor at minimum airspeed air velocity over the muff will be the lowest thus having more time to absorb heat.
Partly
correct, and not complete.

First, It is the speed of the carb intake air through the muff that matters, not airspeed.

Second, As Bubb2 pointed out, the heat transfer to the carb intake air is dependent on at least four things: 1. The temperature of the surface it is in contact with. 2. The distance the mass-flow center of the intake air is from the hot surface. 3. The contact time with the hot surface. 4. The contact area of the hot surface.

So the total heat transfer to the carb inlet air can be limited by any of the above parameters. In the case of my Sutton exhaust, the heat transfer is limited by items 2, 3, and 4 - not 1. If # 2, 3, and 4 were adequately large, then of course #1 could be limiting. In any other airplane I've flown, including mine with the stock Piper exhaust, #1 was indeed limiting. But now, with my current exhaust system, it's not.

I hope I said this in an understandable way!
 
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I knew that a physics teacher could explain it better than I. Gordon where were you when I was taking physics? Opps that wouldn't have been very good, since you would not be here now to keep me on the straight and narrow. :p
 
This might be a dumb question, but....does the engine run good?
In other words, is the problem how the engine runs,
or is it just the readings on your engine monitor that's a cause for alarm?

I'm reminded of when someone mentioned being concerned by high oil temps when towing banners with a C170,
he was told to cover the oil temp gauge with a piece of tape and keep flying.

I have oil pressure, oil temp, and cylinder head temp gauges in my 53 C180- that's all.
They all seem to read what they should, when they should, so I'm happy.
Maybe there's something to that old expression "ignorance is bliss".
 
This might be a dumb question, but....does the engine run good?
In other words, is the problem how the engine runs,
or is it just the readings on your engine monitor that's a cause for alarm?

I'm reminded of when someone mentioned being concerned by high oil temps when towing banners with a C170,
he was told to cover the oil temp gauge with a piece of tape and keep flying.

I have oil pressure, oil temp, and cylinder head temp gauges in my 53 C180- that's all.
They all seem to read what they should, when they should, so I'm happy.
Maybe there's something to that old expression "ignorance is bliss".

I think the answer to that question is; It appears the engine is running fine. The limited ability of my hearing and feeling vibration indicates "no problem". The standard engine gauges (oil press, oil temp, cyl head temp) don't indicate anything to get alarmed about (except these temps appear considerably lower than any other o-520 I know of). And there is something to the "ignorance is bliss" if one finds themselves in data overload and chasing ghosts. But to feel your engine is running fine and intentionally ignore "accurate data" because it may dispel your feeling is not rational behavior.

The EDM-900 has shown the number one cylinder is way too lean in cruise (only 40 degrees ROP with a FF of 18 GPH) and the number 4 is too lean at full power (up near peak with a FF of 24.7 GPH). To spend $20,000.00 on an overhaul and then ignore data that can show "there's problems" is crazy. Kinda like not going to the doctor for a check-up because you feel fine. Lot's of things out there that will kill you while you "feel fine". While premature cylinder failure may not kill you, figuring out what the problem is, getting the engine to run within it's "normal parameters" while reducing the FF a couple gallons per hour can save a person substantial future mechanical problems and a lot of aviation gasoline all of which equals MONEY. Over the life of an engine that could be tens of thousands of dollars.
An advanced engine analyzer is like an aircraft engine colonoscopy. You may not have a problem, but then again, you may.
 
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...and the number 4 is too lean at full power (up near peak with a FF of 24.7 GPH).
How do you know #4 is too lean at full power at (up near peak)? Have you leaned the mixture at full power in order to determine what full power peak actually is? I doubt that anyone on this forum has leaned their engine at full power in order to determine what peak temperature may be. Perhaps your EGT at full power on #4 is near the same temperature as it is when leaned to peak at a lower power setting. That is not saying that it is too hot/too lean at full power.

Try leaning the mixture when at full power and you will see the EGT temp rise even further on #4 than what you are looking at. Don't do this.
 
Bubb2, are you positive your fuel flow K factor is set properly? Your FF reports are high while the symptoms indicate you need more fuel. Unless somebody tweaked your carb you're getting more fuel than most Pponk carbs deliver.
 
How do you know #4 is too lean at full power at (up near peak)?

I know where peak is for number 4 because of a takeoff with the mixture not quite "full rich". Number 4 peaked somewhere (do not have specific temp as EDM only records temps at 6 second intervals) around 1500 degrees egt. The highest FF on that takeoff (again due to the 6 second recording interval and the fact FF readings are not instantaneous as the fuel transducer takes time to "spin up" and stabilize the reading) was just over 23 GPH.
As I indicated before, cylinder 4 is at 1500 at full power with a fuel flow of 24.7 GPH (higher than the STC holder says you need). That's WAY too close to peak yet the engine has higher than required FF. All other cylinders are at least 150 (egt) degrees cooler. Cylinder temps never exceed 315. That same number 4 cylinder behaves totally different at cruise power (2400 RPM, 23 MP) with no indication of running lean.
 
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Bubb2, are you positive your fuel flow K factor is set properly? Your FF reports are high while the symptoms indicate you need more fuel. Unless somebody tweaked your carb you're getting more fuel than most Pponk carbs deliver.

Yes. Indicated total fuel used is equivalent to the fuel to "top of the tanks" within a couple 10th's of a gallon.
 
Check the crossover tube and see what size it is and if it has a open vent/hole in it.
DENNY

The vent is plugged, there are no leaks (although I am re-checking that) and the balance tube is the large IO-520-D tube. I read somewhere about using a specific balance tube for these carbureted 520's but the commenter did not indicate which one that is.
 
bubb2, I don't mean to keep kicking a dead horse and it may be just internet typing which is creating confusion. I'm getting the impression that you do not understand how to determine peak EGT. How do you know that 1500 degrees is peak EGT at full power on that cylinder? You do know that there is no published maximum EGT limitation? The only limiting exhaust temperature which applies to our engines is TIT (Turbine Inlet Temperature) and your engine does not have a turbine therefor your engine has no exhaust temperature limits.

The method to determine peak EGT for any cylinder at any power setting is to gradually pull the mixture toward idle cutoff from full rich while watching the EGT instrument. The temperature will start rising until it achieves a maximum number following which it will start to cool off until the engine stops running. The maximum number is peak EGT, what ever it is. It is a good idea to have at least a 100 degree rise from full rich to peak temperature, preferably 150 degrees.

I assume that the EGT probes were installed correctly, all at the same distance from the exhaust port. This is a variable number but all cylinders must be the same or the temperatures will not have the correct comparison between cylinders. If these distances are not the same the comparison between cylinders will not be accurate.
 
bubb2, I don't mean to keep kicking a dead horse and it may be just internet typing which is creating confusion. I'm getting the impression that you do not understand how to determine peak EGT. How do you know that 1500 degrees is peak EGT at full power on that cylinder? You do know that there is no published maximum EGT limitation? The only limiting exhaust temperature which applies to our engines is TIT (Turbine Inlet Temperature) and your engine does not have a turbine therefor your engine has no exhaust temperature limits.

The method to determine peak EGT for any cylinder at any power setting is to gradually pull the mixture toward idle cutoff from full rich while watching the EGT instrument. The temperature will start rising until it achieves a maximum number following which it will start to cool off until the engine stops running. The maximum number is peak EGT, what ever it is. It is a good idea to have at least a 100 degree rise from full rich to peak temperature, preferably 150 degrees.

I assume that the EGT probes were installed correctly, all at the same distance from the exhaust port. This is a variable number but all cylinders must be the same or the temperatures will not have the correct comparison between cylinders. If these distances are not the same the comparison between cylinders will not be accurate.

I do not mind you beating my dead horse if it helps to increase my understanding of the issue. I see your point as you are correct, the way to know the EXACT peak egt at any power setting is to slowly lean the mixture until the egt begins to drop. With and advanced engine analyzer you do not have to "pull the mixture towards idle cutoff from full rich while watching the egt instrument" you do understand you can pull the mixture to idle cut off with your eyes closed until the engine quits, download the data after you land and know, within a couple degrees where peak egt is for each cylinder at that power setting (assuming of course each cylinder was LOP before the engine quit). THAT'S how I know where peak is for #4 at takeoff (or at least approximately where it is). No, I never "slowly leaned the engine during climb out at full power" but, as I described above I did inadvertently takeoff while slightly lean and cylinder #4 peaked. If a cylinder is indicating a high egt (relative to all the other cylinder egt's) (I do realize the egt temp is not a limit but have read what is important is your egt temperature relative to the other cylinders egt temps) at full power with a fuel flow of 24 GPH yet is still ROP (validated as the egt readout indicates only rising egt temps) and that same cylinder peaks at that same egt temp on a takeoff with a FF of 23 GPH I think one could accurately guess the peak egt of that cylinder at full power. I agree it's a guess but I bet it's within 10 to 20 degrees of true peak. Or is this logic flawed?
 
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THAT'S how I know where peak is for #4 at takeoff (or at least approximately where it is). No, I never "slowly leaned the engine during climb out at full power" but, as I described above I did inadvertently takeoff while slightly lean and cylinder #4 peaked. If a cylinder is indicating a high egt (relative to all the other cylinder egt's)
This is the part which is raising the question. Unless you see a temperature rise followed by a drop or keep your eyes closed and download the rise and drop after you land you have not determined what peak is for that power setting.

Taking off with the mixture slightly out and then pushing it to full rich will not give you any peak information. It will make no difference what brand and model of instrument you are using.
 
I assume that the EGT probes were installed correctly, all at the same distance from the exhaust port. This is a variable number but all cylinders must be the same or the temperatures will not have the correct comparison between cylinders. If these distances are not the same the comparison between cylinders will not be accurate.[/QUOTE]

The egt probes are all the same distance from their respective cylinder. I will point this out. At this time, most responses to my questions are similar to "mine runs good" "my egt temps spread is good" or something to that effect. The only real data I have received, actual temperature readouts, are very similar to what I am seeing. I also spoke with an IA who is suppose to be knowledgeable about this issue and he concurs with the Pelican Perch articles, carburetor systems suck, your always going to have your 5 and 6 cylinder way richer than 1 and 2 and your going to have wide egt temps between cylinders. It's the nature of the beast. I was not satisfied with his answer to the question; Why does the egt temp variance reduce from 250 to about 40, egt temps reduce over 100 degrees across the board allowing leaning of the leanest cylinder (#1) to 100 ROP (same cylinder was running 40 degrees ROP at full rich with no heat) resulting in a fuel flow almost 2 gals. less than where it was, at the exact same power setting without heat? His answer was "pressure."
 
Bubb2,

I think you might still have a fundamental misunderstanding of EGTs. The absolute numbers your EDM reports do not mean a thing, and you cannot compare one cylinder's EGT with another's to learn anything about either cylinder. Alcor, who invented the EGT probe, was so concerned that people would place undue significance on the absolute readings that they refused to even put numbers on their gauges - just a few markings so you could determine needle movement. There are many things that can cause virtually identical EGT probes to read very different EGTs for different cylinders. The hole for the probe might be 1/16" off, the shape (curvature) of the exhaust may alter the exhaust flow past the probe, back-pressure can slow the exhaust flow slightly, and a million other things can cause differences in absolute readings. But none of that matters, because even if one cylinder is reading 200ºF different than the other, it just doesn't matter...

What DOES matter is the "relative" temperature difference between EACH cylinder's PEAK EGT readings, and how much richer (ROP) or leaner (LOP) you are operating THAT cylinder from ITS peak EGT. Every cylinder will peak at a different EGT, and when you operate ROP you want to ensure that EACH of those cylinders is operating ROP. You have to observe all the cylinders, and note which one reaches peak EGT first. That is your "leanest" cylinder (at least that day, in those atmospheric conditions), and when you operate ROP you need to ensure that this "leanest" cylinder is running at least 100ºF ROP at lower power settings, 150ºF ROP at 65-75% power, at ideally at least 200ºF ROP when at full power (full rich mixture).

LOP operations are pretty much the inverse of that. You want to watch all your cylinders as you lean them, and note the LAST one to reach peak EGT. That is your "richest" cylinder (again for at least that day, under those atmospheric conditions), and is the one you will use to measure how far LOP you are operating... You don't want to spend a lot of time doing that leaning thing at high power settings, and the most common technique to get to the lean side of peak is the "big mixture pull" where you smoothly pull the mixture knob until you feel the airplane slow slightly. The feeling is similar to what you would observe if you were driving down a level road at a steady speed, and lifted your foot gently off the throttle. Just a slight "deceleration" is enough to know you're there. Then you confirm with your engine monitor.

You mentioned analyzing the data after you land to prove you were LOP or ROP and by how much... At that point, you're no longer operating the engine, so it does you no good to find out you were operating with some cylinders LOP and others ROP... You've got to be able to do that in the air. Most of the monitors have "lean assist" modes you can use to help with this. The better ones offer both "ROP" and "LOP" assist modes.

You might also want to check with your EDM manual to see if you can change the sampling interval to less than 6 seconds. Most of the monitors can do 1-second intervals, which will capture much finer-grained information for your post-flight analysis...

Good luck!
 
carburetor systems suck,
True. The issue stems from the airflow downstream of the butterfly valve in the carburetor. The only time that there is any consistency in the fuel/air mixture is before it passes the butterfly valve. After that it depends on the angle that the valve is open which creates different turbulence and airflow. The best ratio is produced with the throttle wide open. Also since there is a long intake pipe with separate passages to each cylinder there are different mixtures which get sucked into each cylinder along the way. This causes different fuel/air ratios in each cylinder producing widely different EGT readings.

Your most efficient power setting will be at an altitude where you can operate with the throttle wide open. This will be at about 6000 feet and higher.

A fuel injected engine mixes the fuel with the air at each intake port which provides a more consistent mixture to each cylinder. Thus you can more efficiently fine tune the mixture on a fuel injected engine.

What Jim Parker says is correct.
 
Taking off with the mixture slightly out and then pushing it to full rich will not give you any peak information. It will make no difference what brand and model of instrument you are using.


I don't think that statement is totally correct. If after you land and you download the data and note an egt temperature INCREASE after pushing the mixture in you have just proven you were operating LOP. If after you download the data and note not only a temperature increase but it was followed by a temperature decrease you just found out where peak egt is at full power. Didn't you?
 
I might have a look at the spark plugs if it were mine...electrode/ceramic insulator color and overall condition after a normal cruise flight and minimal ground running afterward. May have already been done? Check the plug wire ends as well for corrosion or contamination. Point being does their color follow the EGT readings and are they in good condition?

Check the mags at cruise and note the EGT response on each. Sometimes that can be interesting with a multi-probe gizmo.

Gary
 
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If after you download the data and note not only a temperature increase but it was followed by a temperature decrease you just found out where peak egt is at full power. Didn't you?
What did you do at the time that the temperature decreased? Pull the throttle back a bit?
 
What did you do at the time that the temperature decreased? Pull the throttle back a bit?

I did increase my carb heat in the climb as my CAT dropped to 20 with full power. That would of course also richen the mixture (and reduce MP). An interesting note though when I went back and looked at the data. Unlike the use of carb heat in cruise the use of carb heat (40 degrees CAT) at full power does not appear to equalize the cylinders. I get an egt temperature difference in cruise of about 250 with no heat and about the same at full power. With carb heat in cruise my egt temp difference is like 45. It does not appear I get the same effect at full power, stays over 200.
 
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Six seconds is a long time between samplings. A lot can happen between samplings so saying you know within a couple of degrees what peak is, is an incorrect statement. You can change the sampling rate, at least you can on the JPI 600 I have to 1 or 2 sec and suspect you can on yours as well.
If indeed you are running LOP at to with the mixture pulled out slightly you have to realize you have a problem that fuel injection will not fix.
At TO power the mixture is purposely set excessively rich to insure against detonation. It should be, as mentioned above 150-200 ROP. As I mentioned before because you are indicating 24gph is NO indication you have adequate fuel flow/mixture to all cylinders.
Again I suggest you do the induction leak test I mentioned several posts back.
Most of these setups run just fine so doubt it is a carburetor problem. It is most likely an induction issue.
I have asked more questions here that I care to admit, Have received a wealth of helpful information all of which has helped me get up to speed on these engines/aircraft we love to fly. We are all here to help and learn and most importantly to enjoy this most wonderful ability our machines offer us.

Tom
 
Flew the airplane with no air filter. Not much different than with one. The pressure restriction theory did not seam to hold up. I cycled the carb heat on and off several times. Each time the fuel flow increased with carb heat. About a gallon increase in cruise accompanied by about an inch drop in manifold pressure. OAT was 11 and the unheated carb temperature today was +1. Full carb heat could only get it up to 35. That 5 degree difference from my usual 40 degrees seamed to make a difference as my egt differential improved with the heat but not as well as when I can get the carb to 40. Never went below 100. I immediately did a compression check when I landed and confirmed all cylinders at or above 78.
I have been advised to ensure the intake manifold tube assembly's are aligned. I plan to do this, pressure check the system, then collect more data.
 
Are the screws holding the carb halves together loose? The mounting flange nuts tight? Does the carburettor move when the carburettor heat is operated? I am now thinking you are looking for something really simple but easily overlooked. Throttle position changing when carb heat is operated because carburettor is loose and moving. Air leak at carb gasket because the screws have loosened.
 
Are the screws holding the carb halves together loose? The mounting flange nuts tight? Does the carburettor move when the carburettor heat is operated? I am now thinking you are looking for something really simple but easily overlooked. Throttle position changing when carb heat is operated because carburettor is loose and moving. Air leak at carb gasket because the screws have loosened.

The carb appears tight, no movement. I did do a pressure check on the intake system last year when it was becoming clear there was something odd going on. My balance tube has a treaded plug I am able to hook up to compressed air. I blocked the carb inlet with paper towels and pressurized the system checking for leaks with soapy water. None found. There was obvious air leakage past those paper towels. Once I adjust the intake tubes and replace all the gaskets I'll re-check the system. This time I think I'll use a plastic garbage bag or something similar to get a better seal when I block the carb inlet.
 
What is the issue we are chasing here? (Thread title: carb heat for better fuel atomization)

uneven EGT's?
wide EGT spread?
FF change with carb heat application?


one very high CHT? If its one high cylinder, maybe its a cylinder problem that has gone undiagnosed. Valve guide or seat? Rings? Wrong spark plug heat range? Weak or high resistance spark plug?

XXXXX one lean cylinder? you stated in first post that peak on a certain cylinder is 1490egt and full rich at 1000msl its 1450egt. Not rich enough! Right? How is the CHT FOR THAT CYLINDER?



where you live Bubb? Hope you find the prob and share the data! Where you live?
 
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What is the issue we are chasing here?

uneven EGT's?
wide EGT spread?
FF change with carb heat application?

one very high CHT? If its one high cylinder, maybe its a cylinder problem that has gone undiagnosed. Valve guide or seat? Rings? Wrong spark plug heat range? Weak or high resistance spark plug?

where you live Bubb? Hope you find the prob and share the data! Where you live?

I'm out in Chugiak.
I do not think it is a cylinder problem, All cylinders check OK. The main problem is that in cruise, full rich, cylinder #1 is very close to peak egt. It runs about 40 degrees ROP (don't think this is an induction leak as this is one of the richest cylinders on take off). This results in a very excessive fuel flow. Very wide egt temperature differentials indicating inconsistent fuel/air mixture being distributed to the cylinders. This wide variation is most apparent at full power when cylinder 4, for whatever reason, indicates 300 degrees higher than the others (in cruise it's one of the richer cylinders). I suspect it may be too lean at full power. The egt differential reduces with power reduction but is still above what is considered normal for a carburetor. The main puzzlement is this same engine becomes one of the best fuel/air distributed carbureted engines you could find with the application of carb heat. Does anyone here have a carbureted 520 engine that runs with an EGT temp differential lower than 45 degrees (this engine does but only with carb heat, about 250 degrees with carb heat cold)? I've talked with guys who have GAMI injected 520's who see numbers that low (even lower). I would love to see numbers from other engines.
The CHT's on this engine are very low. I think the max I have ever recorded on any cylinder was 320. Normal temps for #1 in cruise is 305. #4 has the hottest EGT at full power, about 1550 (over 300 degrees hotter than the coolest cylinder) yet CHT on that cylinder might get to 310 in climb and cools back down to about 300 in cruise (this is a 1575 pound 1954 180 so climbs to my normal cruising altitude of 1000 feet are of pretty short duration). Oil temp is also very low, I have almost the entire oil cooler taped over and only get oil temps in the 140's in winter.
 
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Absolute EGT readings are meaningless. Individual EGTs can vary dramatically for a host of reasons, including variation between probes, curve of the exhaust pipes, distance of the probes from the exhaust valve, distance of the probes from exhaust pipe curves (both up- and down-stream), etc. Even 300ºF differences are absolutely nothing to worry about. That's why Alcor (the company that originated EGT measurement systems for airplane engines) refused to put any temperature readings on their gauges - they feared pilots would obsess over them, rather than viewing the system as a "trend" management tool as was intended.

It's the CHTs you should be concerned with for long-term engine health. There can be slight differences in CHT probe readingss, but swapping probes between cylinders should produce very similar CHT readings for that cylinder. The notable exception to this is that the "ring-type" probes that mount under the spark plugs typically read 50-80ºF (or more) higher than the "well-type" probes. The well-type probes provide more realistic readings that are aligned with the engine manufacturer's operating recommendations. (Yet most single-cylinder EGT systems provided by the airframe manufacturer use the "ring-type" probes... Go figure...)

At higher power settings, significant differences in CHT readings – especially when combined with higher-than-desired CHT readings on one or two cylinders – may well indicate that there is a problem with the cooling airflow over those hotter cylinders. A well-designed air cooling system can be rendered ineffective by leaking baffles, torn/cut baffle seals, mud dauber nests in the cylinder fins, etc. Those CHT differences (especially when resulting in elevated CHTs) are DEFINITELY important, and should be investigated/resolved ASAP.

High CHTs damage exhaust valves, seats, and guides. A bent or warped exhaust valve creates "hot spots" on the piston and cylinder head that can lead to massive problems. Keeping your engine's CHTs well below the redline in high-power situations, and below the yellow-zone in cruise-power situations will increase the engine's longevity tremendously.

PS - The CHTs you're reporting above are excellent, and would appear to indicate a very healthy cooling system. Unless you see cruise CHTs above about 380ºF, I would be very happy with your engine's cooling system!
 
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