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  #1  
Old 04-16-2021, 07:37 PM
RhinoDrvr RhinoDrvr is offline
 
Join Date: Jun 2014
Location: Lemoore (Fresno), CA
Posts: 157
Default High EGT's (1500+)

Hi all,

I've listened to Mike Busch's webinars and such, and have gathered that EGT is meaningless on a non-turbo Lycoming, and is simply a point of reference for setting fuel flow.

That said; at low altitude, LOP, my EGT's are around 1550 F, which turns my G3X engine monitor from green to yellow. I can reset this threshold, but before I do I wanted to make sure I wasn't missing some limit.

I know in turbocharged installations 1650 is generally referenced as maximum turbine inlet temperature (TIT), but I obviously don't have a turbine to worry about. So, is it safe to say that my EGT's of 1550 are completely fine, and I should just reset the yellow caution to 1600 degrees, and the redline to 1650?

The high EGT's began occurring when I timed my PMAG's 1 tooth after TDC, which makes sense. Less advance = higher EGT's, and lower CHT's.

TL,DR - Is it acceptable to set the caution and warning ranges on the G3X to 1600 and 1650 degrees respectively, or are EGT's in the high 1500's something to be aware of. I don't want to unknowingly cause damage or excessive wear to my exhaust components.
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  #2  
Old 04-17-2021, 12:11 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
Posts: 355
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Hi Evan, Dynon Skyview comes also with preset green/yellow/red EGT ranges. i found that annoying and changed it to all green.

As you said absolute EGT values for us normally aspirated are meaningless. Imagine you have installed your EGT probes one foot lower... you get the idea. i see no problem and your 1500...1600 indications sound just normal.

Last edited by KayS : 04-17-2021 at 12:16 AM.
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  #3  
Old 04-17-2021, 12:15 AM
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rv8ch rv8ch is offline
 
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I can give you a data point - I can get to right at 1500f EGT when running about 10gph at 4500 or 5500 ft WOT. At 16GPH I show about 1180f.

Not saying this is right or good or confirms your setup is ok. I don't run LOP for more than just short tests as I have not really flown much out of my area.

My pmags are programmed like this using the eicommander:

ADV max: 33.6
ADV shf: -1.4
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  #4  
Old 04-17-2021, 03:47 AM
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mike newall mike newall is offline
 
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Re time the P-Mags to TDC. Also check all of your pipes from the inlet manifold to the P-Mags.

We had exactly the same issues accompanied by low power. Brad was brilliant and said check for leaks in the pipes, if no leaks, re time to TDC.

We found a pipe had come off.

This stops the P-Mags from advancing, they run in base get yourself home mode but are well retarded. Hence you have burning fuel leaving the cylinders on the exhaust. At that, your egt probes will be toast !
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  #5  
Old 04-17-2021, 06:23 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by mike newall View Post
Re time the P-Mags to TDC. Also check all of your pipes from the inlet manifold to the P-Mags.

We had exactly the same issues accompanied by low power. Brad was brilliant and said check for leaks in the pipes, if no leaks, re time to TDC.

We found a pipe had come off.

This stops the P-Mags from advancing, they run in base get yourself home mode but are well retarded. Hence you have burning fuel leaving the cylinders on the exhaust. At that, your egt probes will be toast !
Mike, I assume "a pipe had come off" means you had one leaking intake gasket. It would make little or no advance difference in cruise at WOT, as the deltaP across the leak would only be equal to intake tract loss (about 14.4" H2O total for the standard Lycoming horizontal system, for example), and pretty much limited to the tract with the leak...which may or may not be the one tapped for manifold pressure. At low altitude, throttled, the deltaP would be higher, but the effect is not hidden. The pilot's manifold pressure gauge is showing the same pressure seen by the P-mags. The P-mags care not if the pressure is the result of altitude or a leak, or a properly throttled intake. They just advance per the pressure seen on the MP gauge, and RPM.

Rebranding standard Lycoming timing as "base get home mode" is spin worthy of a politician. Standard timing (base P-mag timing) is not "well-retarded". It's normal.

At normal timing, combustion is complete before the the exhaust valve opens. With advanced timing it's complete even earlier. There may be fuel in the exhaust stream, but that would be a function of a mixture setting on the rich side of peak, where there wasn't enough available oxygen to combine with all the carbons. Any burning is limited to a few strays which didn't get married earlier in the game. Indicated EGT is a function of pressure at exhaust valve opening. And given the OP is concerned with high EGT, I believe we can safely assume he is not full rich. Peak EGT closely corresponds to stoich, where combustion is fastest.

Consider the operating principle of the common O2 sensor.
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Last edited by DanH : 04-17-2021 at 06:30 AM.
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  #6  
Old 04-17-2021, 06:48 AM
lr172 lr172 is offline
 
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Assuming this is a new condition, I would be looking at a timing error or inop condition on one of the Pmags. 1550 LOP seems high to me, though I understand that each setup is different. Not a problem being that high, only that it is an indication that your timing is too retarded. Only time I have seen 1500+ when LOP and lower power settings is when one ignition went bad. Running the cylinders on one plug substantially retards the effective timing and will drive the EGTs a good 100* above normally.

Also possible that you took out too much timing and are now well below optimum and leaving power on the table. Only way to tell is with a timing gun.
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Last edited by lr172 : 04-17-2021 at 06:52 AM.
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  #7  
Old 04-17-2021, 06:57 AM
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mike newall mike newall is offline
 
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The sense pipe from the inlet manifold had split and detached from the T piece between the mags. The rest is what Brad said as best as I can remember.

In our case, when you got to altitude and the P-Mag saw reducing pressure naturally, it must have advanced.
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  #8  
Old 04-17-2021, 08:45 AM
RhinoDrvr RhinoDrvr is offline
 
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All,

I know why the EGT is at 1550. The PMAGís are timed 1.4 degrees before TDC which equates to a base timing of 23.6 degrees BTDC vice Lycomingís recommended 25 degrees.

This limits the PMAGís max advance on the top end, however, and makes it easier to control CHTís (they wonít exceed 400 now even during a VX climb on a 100 degree day.

As far as power loss, I canít tell, so I donít care. Iíd rather not stress my engine with more advance than is necessary for a power advantage that I cannot detect in an airplane that is over-powered as is.

I did have an intake leak, but fixed it with the SDS intake gaskets. Iíve conducted the in-flight lean test, GAMI spread test, and in flight mag-checks, and all show good results.

Iím seeing the 1550 number at peak EGT, and only at low altitudes (below 4000í). At high altitude peak EGT is lower (1450 or so). I normally cruise around 60% power for economy, and about 25 deg LOP, which puts me around 1525 EGT at low altitudes. Just want to confirm that Iím not damaging any exhaust components by tooling around with EGTís that hot. Up high (8000-12000) where I normally cruise, EGTís at 25 LOP are closer to 1425, which is more like in line with what I expect (and this is due to the PMAGís advancing at high altitude and reduced MP).
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  #9  
Old 04-17-2021, 09:22 AM
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Carl Froehlich Carl Froehlich is offline
 
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Evan,

Some thoughts:
- pMag timing advance if much more about cruise efficiency than power. For that matter, full rated power (take off) timing with a pMag set per the instructions (at TDC for parallel valve engines) is about the same as a standard mag.
- I fully agree that timing the pMag at something ATDC will result in lower CHTs, but this is at the expense of power and fuel efficiency. You can achieve the same CHT reduction with the pMags set at TDC if you pull back on the throttle and/or keep the mixture knob in.
- If your mission is to win a time to climb competition, retard the timing as you donít care how much engine efficiency you a loosing along with wasted fuel. If you have a more rounded mission, time the pMags per the installation instructions and run with the jumper in. The jumper in provides timing from 25 degrees to 34 degrees BTDC (at cruise RPM) - I have found no data that suggest more advance is beneficial. Now use the other tools available to you to keep CHTs below your target (mixture, throttle and climb speed).

Get the most out of every drop of fuel you put in the engine.

Carl
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  #10  
Old 04-17-2021, 09:42 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by mike newall View Post
The sense pipe from the inlet manifold had split and detached from the T piece between the mags.
Ahhh, split rubber or plastic tubing? "Pipe" suggests something different on this side of the pond.

With an open port, the P-mag would not advance from base timing at low altitude. With the engine throttled at low altitude, it would raise EGT as compared to EGT with advanced timing, although I don't think it would be a huge amount, as again, the engine is throttled. Regardless, you made a good suggestion; the OP should indeed check to see if perhaps the tube got knocked off a nipple when he re-timed, or just wasn't re-connected after the blow.

That said, base timing is not retarded or a limp home. It is more or less the same as standard fixed timing. Calling it anything else is BS, and I don't care who said it.

Returning to Evan's interest...

Quote:
Originally Posted by RhinoDrvr View Post
Just want to confirm that I’m not damaging any exhaust components by tooling around with EGT’s that hot.
Unlikely, for several reasons.
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Last edited by DanH : 04-17-2021 at 09:54 AM.
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