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IO-540 Takeoff EGT is around 100F ROP

bsvantho

Active Member
I have seen that full-rich full power takeoff for Lycoming engines has the EGT typically quoted around 200-250F ROP.

I typically see only about 100-120F difference from the takeoff EGT to peak EGT. I suspect I am running a bit lean at takeoff, though the fuel flow value does not seem to be unusually low. CHTs will jump slightly above 400F if I maintain a full power climb without rolling back MP a bit. Engine has about 125hours. I am trying to determine if an adjustment should be made.

I have a Thunderbolt IO-540 with AFP FM-150 and 1 Surefly + 1 MAG ignition.
Injectors are balanced - spread is usually .3 GPH at peak EGT.
At takeoff (full-rich) Fuel flow is 22.8GPH, RPM 2690, MAP 28.2", OAT 25C, field elevation 980ft.
EGTs are 1315-1365F - peak EGT is around 1450-1460F.

Take off at time 14:25, peak EGT at 22:44 -
Actual Engine Data
 
Do you have .025 or .028 injector nozzles? I have the former and see similar fuel flows and EGTs at those ambient temps. With the .025 nozzles, you will see a bit lower flow rates than other who have the stock .028 nozzles. AFP recommends the 025 nozzles for the 540, so suspect that is what you have. The high CHTs can come from many factors, not the least of which is advance levels on your EI.

Best power is around 80-100 ROP and anything more is just wasting fuel, assuming you can keep the CHTs in line and keep the advance curve at 25* or lower during T/O. IMHO 250 ROP is too fat. Wastes gas and reduces power output.

Larry
 
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Do you have .025 or .028 injector nozzles? I have the former and see similar fuel flows and EGTs at those ambient temps. With the .025 nozzles, you will see a bit lower flow rates than other who have the stock .028 nozzles. The high CHTs can come from many factors, not the least of which is advance levels on your EI.

Best power is around 80-100 ROP and anything more is just wasting fuel, assuming you can keep the CHTs in line and keep the advance curve at 25* or lower during T/O. IMHO 250 ROP is too fat. Wastes gas and reduces power output.

Larry

My nozzles vary between .0245 and .255, so yes that makes sense my flow would be a bit lower.

I think I answered my own question though. The reason my spread between full rich EGT and peak EGT is small is because I am comparing takeoff power setting full rich EGT with cruise power setting peak EGT, which is not valid. I reviewed the AFP manual and they say to pick a power setting like 2400/24" and check the EGT at full rich and peak without changing the power setting. I suspect I will see closer to 200F spread with that test.

Yes the advance is the engine fixed timing of 25 BTDC for T/O on the Surefly. That is a good point though. The peak EGT at cruise power will be somewhat lower since that is where the ignition advance should be greater than 25.
 
Best power is around 80-100 ROP and anything more is just wasting fuel,

I’d suggest caution with a blanket statement like that. Many aircraft engines are set up to run overly rich at 100% power, to provide detonation margin.
 
My nozzles vary between .0245 and .255, so yes that makes sense my flow would be a bit lower.

I think I answered my own question though. The reason my spread between full rich EGT and peak EGT is small is because I am comparing takeoff power setting full rich EGT with cruise power setting peak EGT, which is not valid. I reviewed the AFP manual and they say to pick a power setting like 2400/24" and check the EGT at full rich and peak without changing the power setting. I suspect I will see closer to 200F spread with that test.

Yes the advance is the engine fixed timing of 25 BTDC for T/O on the Surefly. That is a good point though. The peak EGT at cruise power will be somewhat lower since that is where the ignition advance should be greater than 25.

I also have the Surefly with a IO540. I think I have the opposite problem and am running a bit rich. I see 28 GPH FF with a airport elevation of 840 MSL. I am running 9.5 to one pistons and a CAI. Keep in mind that pulling power may not help with cooling and with the Surefly in advance mode might hurt. The Surefly will only advance the timing once the manifold pressure is below 25 inches. If you maintain full power that will happen around 6000 feet.
G
 
I’m not an expert, but I do have some thoughts about what I would try.

By certification an aircraft engine cannot be harmed with the red knob when below 65% power. So I’d figure out what fuel flow makes 65% power in the lycombing docs then climb to whatever altitude restricts power to 65% then lean to peak at WOT and see if the fuel flows line up. If they do I would note the EGT as the max EGT for my airplane.

If the full rich/full throttle EGT was 150* or more colder than that number you get at 65% then I’d be happy with that. You are basically 150 cooler than max which gives some detonation margin.

I’d also call Don to confirm my plan....

Schu
 
Brendon,

At your elevation and with the MAP & RPM you quoted your takeoff fuel flow should be 24USG/Hr, or not far from it.

So first of all, get your FCU sent back and flowed correctly.

To add credence to this, you EGT's are backing up this. Given you have an EI which will always have more advance than a magneto, this will create a lower EGT, and normal EGT for a correctly timed IO540 is 1300dF (nominally). The advanced timing should yield 1250-1275 range, and yet you have mid 1300's. This confirms too low a fuel flow.

I would also knock out two degrees of advance from the EI.

Happy to help if you need more.
 
I think your fuel flow is too low too, but perhaps by even more than suggested by RV10inOz. My IO-360-A (200 hp) pulls almost 20 gph at sea level takeoff power, 150F ROP.

So if you have a 260 hp IO-540, I would suggest your take-off fuel flow should be about 26 gph. I suppose if you have the lower compression 235 hp, then something around 24 gph would be about right.

I see you have an FM-150, which I think is a bit small for a 540, and may be somewhat restrictive. In that case, your fuel flows will be lower, cuz your airflow is lower too. Still, something around 24-ish.
 
I see you have an FM-150, which I think is a bit small for a 540, and may be somewhat restrictive. In that case, your fuel flows will be lower, cuz your airflow is lower too. Still, something around 24-ish.

My Thunderbolt IO-540 came from Lycoming with an FM-150... I doubt they are installing things that are a “bit small”. I questioned it too and both Lycoming and Don say its fine.
 
I typically see only about 100-120F difference from the takeoff EGT to peak EGT. I suspect I am running a bit lean at takeoff, though the fuel flow value does not seem to be unusually low. CHTs will jump slightly above 400F if I maintain a full power climb without rolling back MP a bit. Engine has about 125hours. I am trying to determine if an adjustment should be made.

Do the 24/24 check and I think you'll leave it alone. Slightly above 400 in continuous climb at max power mixture is better than average for RV-10 installations.

You have a T-bolt. Dig out your documents. Does supplied data identify fuel flow at a max power, and the resulting BSFC?

In general, minimum fuel flow for a lycoming at rated power is about 0.50 BSFC. We can't know how much mass you're pumping at the reported point (a function of density, VE etc), so the flow of 22.8 can only be treated as a ballpark indicator. Ballpark, 22.8 x 6 x 2 says it's enough fuel for 274 HP given standard sea level conditions, or a little rich with altitude gain.

Can you pour on more fuel? Sure. The power vs mixture curve is not steep, so you won't lose more than a few percent. You'll lose a few feet per minute, then probably try to climb at a lower IAS to compensate, which will reduce dynamic pressure, which will push CHT back up...

Concern with detonation margin has a practical side. Dyno data puts detonation onset at about 50 ROP, with some variation for ignition timing, CR, and octane. However, that data is taken under worst case conditions, like 475 CHT and max oil temp. Most of us have good instrumentation and would never allow that worst case. And anyway, a steady "slightly over 400" indicates you have normal combustion.

The FM 150 flows a little more air than an RSA-5, the old norm for a 540. Good choice for an RV-10.
 

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I’d suggest caution with a blanket statement like that. Many aircraft engines are set up to run overly rich at 100% power, to provide detonation margin.

I suppose that is a fair point. However, those actively adapting their engines (assumed the OP was one of them) should understand that and have taken measures to ensure detonation risks are managed. I can see why a manufacturer would take this approach to account for all scenarios, but it is not necessary when folks are designing engine performance curves and actively maintaining and monitoring their engines.

I added a caveat about high CHTs and timing advance, as those are the two largest factors that can cause detonation and create an exception to my statement.

Larry
 
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Brendon,

At your elevation and with the MAP & RPM you quoted your takeoff fuel flow should be 24USG/Hr, or not far from it.

So first of all, get your FCU sent back and flowed correctly.

To add credence to this, you EGT's are backing up this. Given you have an EI which will always have more advance than a magneto, this will create a lower EGT, and normal EGT for a correctly timed IO540 is 1300dF (nominally). The advanced timing should yield 1250-1275 range, and yet you have mid 1300's. This confirms too low a fuel flow.

I would also knock out two degrees of advance from the EI.

Happy to help if you need more.

Where does this 24gph number come from? I talked with Lycoming and they said the chart says around 21gph for D-series. I looked at that chart as well, but it seems that is for best power, not full rich. So not very helpful.

The Surefly EI operates in fixed timing at high MP ( above 25" ) at all RPMs. In my case it is set to the same 25 BTC as the magneto. The mid 1300's EGTS are at full power so advance should not be an issue here unless the EI is not working properly. I cannot adjust advance, only switch it to fixed timing mode.

I spoke with AFP about the fuel flow. Their comments are that fuel control delivers a fuel air ratio to the engine, not a fuel flow. The fuel flow is based on how much air the engine pulls through the fuel control unit. Which of course make sense.

I reviewed some of my flight data and found that my EGT delta from full rich is to peak is about 220-230F at cruise low altitude. They said from that data, it is on the rich side. They quote 185-220F as normal at 24"/2400RPM under 4000ft. Is it possible that I am running a bit lean at takeoff power, but somewhat rich at lower power? That may be an argument to have it flow tested.

It would be nice to see some data from others with the same setup.
 
Brendon, if you fo desire a bit better cooling you can via the dip switches set the Surefly to 23” base timing with advance. I run this on my aircraft but I have 9.5 to 1 pistons.
G
 
Given you have an EI which will always have more advance than a magneto....(snip)..I would also knock out two degrees of advance from the EI.

Why does an EI "always have more advance than a magneto"?
 
W I talked with Lycoming and they said the chart says around 21gph for D-series. I looked at that chart as well, but it seems that is for best power, not full rich. So not very helpful.

If Lyc says best power is 21 GPH and you are flowing 23 GPH, why be worried? Lyc doesn't list a full rich fuel flow as it is not really relevant to anything. Designers may add a specific amount of additional flow, beyond best power, to offset unforeseen factors that may reduce the detonation margin. The lawyers love that. Remember,. they have to assume that a bad mechanic messed up the baffling, a birds nest developed in front of the cyl and someone let the timing drift to 30* advanced (mags do that as they wear). How much margin you build in should be based upon the likelihood of you or your mechanic making mistakes. If that is high, then target 28, like most of the airframe mfr's do. They don't really care that you're wasting gas and losing power; They list their specs at best power, not full rich.

Larry
 
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My Thunderbolt IO-540 came from Lycoming with an FM-150... I doubt they are installing things that are a “bit small”. I questioned it too and both Lycoming and Don say its fine.

Note that the IO-390 usually installs an FM-200.

Bob Mills took an RSA-5 (same size as an FM-150?) off of his IO-540 and installed an FM-300 with a very noticeable increase in power, reduction in his lap times. It is just breathing better. To be fair, it also got a better-flowing induction plenum at the same time.

Based on those observations, I think the FM-150 is a 'a bit small'. For most missions, you probably have plenty of power. But perhaps not all the power the engine is capable of.
 
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Concern with detonation margin has a practical side. Dyno data puts detonation onset at about 50 ROP, with some variation for ignition timing, CR, and octane. However, that data is taken under worst case conditions, like 475 CHT and max oil temp. Most of us have good instrumentation and would never allow that worst case. And anyway, a steady "slightly over 400" indicates you have normal combustion.

DanH, This performance chart is for "worst case" in most respects, but only 26" MAP. What does the detonation margin look like at 30" MAP?
 
DanH, This performance chart is for "worst case" in most respects, but only 26" MAP. What does the detonation margin look like at 30" MAP?

No 30" MP charts, only "full throttle", with pressure undefined. Nor do the graphs show a clear peak. They didn't pull that far at full throttle.

The 2700-28" charts don't have a well defined peak, but there's a suggestion of one (attached below). Best I can tell, detonation onset is about 90F ROP. That's right at max power, but remember, CHT is 475F, oil 245, IAT 103, all on a 540K, which the FAA considers the worst case NA engine.

The OP reported 22.8 GPH at 2690 and 28.2. The detonation onset vs fuel flow chart puts 22.8 on the rich side of DO for the 540K.
 

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If Lyc says best power is 21 GPH and you are flowing 23 GPH, why be worried? Lyc doesn't list a full rich fuel flow as it is not really relevant to anything. Designers may add a specific amount of additional flow, beyond best power, to offset unforeseen factors that may reduce the detonation margin. The lawyers love that. Remember,. they have to assume that a bad mechanic messed up the baffling, a birds nest developed in front of the cyl and someone let the timing drift to 30* advanced (mags do that as they wear). How much margin you build in should be based upon the likelihood of you or your mechanic making mistakes. If that is high, then target 28, like most of the airframe mfr's do. They don't really care that you're wasting gas and losing power; They list their specs at best power, not full rich.

Larry

Definitely not worried, this is mostly a learning experience. I was trying to understand what I was observing with regard to EGTs, but it was a flawed observation. I used to fly a Cherokee Six (260HP version) on occasion and recall much higher fuel flows. I actively manage the engine and have not been concerned with detonation, especially with standard compression and running 100LL. The CHTs seem to be in line with other RV-10s give or take and only during break in did I have to really watch them close.

There is a lot of good information here and now I have a better understanding of all the contributing factors. I am an engineer, but am still pretty new to physics/thermodynamics involved in these engines. Confirmation that I am in line with the standard operating parameters is good enough for me, I am not looking to fix something that isn't broken.
 
No 30" MP charts, only "full throttle", with pressure undefined. Nor do the graphs show a clear peak. They didn't pull that far at full throttle.

The 2700-28" charts don't have a well defined peak, but there's a suggestion of one (attached below). Best I can tell, detonation onset is about 90F ROP. That's right at max power, but remember, CHT is 475F, oil 245, IAT 103, all on a 540K, which the FAA considers the worst case NA engine.

The OP reported 22.8 GPH at 2690 and 28.2. The detonation onset vs fuel flow chart puts 22.8 on the rich side of DO for the 540K.

For those that are following along, what DanH means is that the 28" MAP data does not go lean enough to show a peak EGT, but it is 'suggested' where that peak is. So you can see where the detonation onset is (the black squares on Dan's chart). A key take-away, comparing the 26" MAP and 28"MAP chart is that the detonation onset shifted from about 50 ROP to 90 ROP as the manifold pressure increased. At sea level, where a good-breathing engine may see 30" MAP, may expect the detonation margin to shift a bit more to the rich side--perhaps to 120F ROP (that is just a guess).

Another key factor in this is spark advance/mag timing. It would only take a small amount of advance from where these data were taken to bring the detonation onset to an even richer condition. Neither of the charts Dan posted show what the timing setting is, but it would be understood to be the normal mag timing setting on the data plate of a IO-540-K (25 BTDC?).

So suppose you have an EI system that has the base timing set to, say, 26--27 BTDC, and at 26" MAP, might give a little bit of advance, to, say, 28--29 BTDC. If you are only 120F ROP you could easily experience borderline detonation. It might show up as a sort of pitted, bubbly, foamy looking surface on the spark plug center electrode. I've seen it.
 
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A key take-away, comparing the 26" MAP and 28"MAP chart is that the detonation onset shifted from about 50 ROP to 90 ROP as the manifold pressure increased. At sea level, where a good-breathing engine may see 30" MAP, may expect the detonation margin to shift a bit more to the rich side--perhaps to 120F ROP (that is just a guess).

First, a reminder...the above data, and the charts below, were taken under operating conditions no sensible pilot would ever accept...475 CHT, 245 oil temp, +100F IAT. It's not a natural condition; the dyno operator throttles cooling air supply.

Charts below are from a Lycoming test comparing an ethanol fuel with 100LL, this time in a common IO-360A. On the 2700-28.5 chart, although detonation onset (the noted point in the previous documents) is about 60 ROP, peak detonation frequency is at peak EGT, and even then, it's only happening in less than 5% of combustion events. Although very high, CHT is falling, not rising, as power falls near peak EGT and beyond.

The other chart is a check at the "max manifold pressure" line on the power charts, a little more than 4 over square. Onset is about 75 ROP, with max intensity again near peak EGT, and a little more than 10% of cycles.

Low levels of detonation are considered acceptable. Given the full plots, Lycoming was not worried about ruining their test engine, and those who have attended a course at Ada have watched the APS guys push into detonation at will. The takeaway is that it's not like suddenly crossing an imaginary line and having the engine grenade.

Another key factor in this is spark advance/mag timing. It would only take a small amount of advance from where these data were taken to bring the detonation onset to an even richer condition. Neither of the charts Dan posted show what the timing setting is, but it would be understood to be the normal mag timing setting on the data plate of a IO-540-K (25 BTDC?).

20 for the 540K, 20 for the 360A. Agree with Steve's caution. I really, really wish we had some hard data in the public realm for 100LL and varied advance values. For now, CHT is the telltale, and the best defense.
 

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For those that are following along, what DanH means is that the 28" MAP data does not go lean enough to show a peak EGT, but it is 'suggested' where that peak is. So you can see where the detonation onset is (the black squares on Dan's chart). A key take-away, comparing the 26" MAP and 28"MAP chart is that the detonation onset shifted from about 50 ROP to 90 ROP as the manifold pressure increased. At sea level, where a good-breathing engine may see 30" MAP, may expect the detonation margin to shift a bit more to the rich side--perhaps to 120F ROP (that is just a guess).

Another key factor in this is spark advance/mag timing. It would only take a small amount of advance from where these data were taken to bring the detonation onset to an even richer condition. Neither of the charts Dan posted show what the timing setting is, but it would be understood to be the normal mag timing setting on the data plate of a IO-540-K (25 BTDC?).

So suppose you have an EI system that has the base timing set to, say, 26--27 BTDC, and at 26" MAP, might give a little bit of advance, to, say, 28--29 BTDC. If you are only 120F ROP you could easily experience borderline detonation. It might show up as a sort of pitted, bubbly, foamy looking surface on the spark plug center electrode. I've seen it.

All fair points. However, it should be noted that the K series is an angle valve engine with different characteristics than the typical parallel valve engine used on most 6 cyl RVs. Lycoming recommends 20* of advance instead of the typical 25 on this engine. Don't know if that is due to chamber shape or simply sensitivity to detonation. Either way, we can't necessarily assume that the 540 C/D series will produce detonation as easily as the K series.

The beauty of ignition systems with customizeable maps is meaningfull here. I run 21* above 27" of MAP to provide additional margin. Toobuilder and others have done extensive testing, showing no power loss in high MAP ROP operations by dropping as much as 5 degrees from the Lyc recommendation. And this makes perfect sense, as Lyc had to find a mid-point recommendation due to the limits of fixed timing.

Definately not trying to be loose here with regard to preventing detonation. It IS a serious thing and MUST be respected. Just throwing more data out there to help us all understand the risk and potential.

Larry
 
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All fair points. However, it should be noted that the K series is an angle valve engine with different characteristics than the typical parallel valve engine used on most 6 cyl RVs. Lycoming recommends 20* of advance instead of the typical 25 on this engine. Don't know if that is due to chamber shape or simply sensitivity to detonation. Either way, we can't necessarily assume that the 540 C/D series will produce detonation as easily as the K series.
Larry

The angle-valve engines are 8.7 CR, which definitely aggravates detonation. IO-360A engines were data-plate timed at either 20 or 25 BTDC depending on installation. I run mine at 25, operating from a 2000 MSL field. My take-off power setting is 130F--150F ROP.
 
The angle-valve engines are 8.7 CR, which definitely aggravates detonation. IO-360A engines were data-plate timed at either 20 or 25 BTDC depending on installation. I run mine at 25, operating from a 2000 MSL field. My take-off power setting is 130F--150F ROP.

8.9 CR for angle valve 390 and 580.
 
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