Multipoint EGT- How close should they be in temperature?
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James331
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James331
More importantly what are the CHTs and oil temp, fuel burn (for %HP) etc, EGTs are the very bottom of my list of concerns.
On mine think they spread about 3 bars on my JPI, hottest was about the same as you, that's on a IO520
On mine think they spread about 3 bars on my JPI, hottest was about the same as you, that's on a IO520
JohnAJohnson
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With tight intake runners and rubber sleeves (no intake leaks), My O-360-A1F6D runs at most 120 degrees difference but at cruise, they're usually within 50 degrees. Carbs will always be higher than IOs, all other things being equal. I've been told that the closer they are, the more likely you can successfully run lean of peak.
FastEddieB
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Fast Eddie B
Absolute EGT is highly variable, dependent on probes that have some variation and placement in the exhaust that can vary slightly. So I wouldn't obsess over slight variations in the raw numbers.
"Spread" in when they peak is meaningful when trying to balance the injectors in a fuel injected engine. With a carb, you're pretty much at the mercy of induction system variables.
"Spread" in when they peak is meaningful when trying to balance the injectors in a fuel injected engine. With a carb, you're pretty much at the mercy of induction system variables.
MooneyDriver78
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Tom
My EGT spread is 80 degrees, my CHT is 40.
Absolute EGT is largely irrelevant. The temperature is going to vary quite a bit with the probe placement. Where the EGT peaks with relationship to your mixture setting is the useful number. A well tuned injected engine can have them all peak within a very small range of mixture adjustment.
JOhnH
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The O360 in my Cessna had an egt spread around 150; sometimes more.
My IO520 in my Bonanza has a spread generally less than 50.
But as has been said, specific numbers are pretty meaningless because they vary so much with placement and condition of the probe.
My IO520 in my Bonanza has a spread generally less than 50.
But as has been said, specific numbers are pretty meaningless because they vary so much with placement and condition of the probe.
FastEddieB
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Fast Eddie B
Alcor seems to agree!
That's what I put in a C150 years ago and it was pretty worthless. With a carb, all I could really do was lean to roughness and then enrichen just a bit, regardless of what the single-probe EGT was telling me.
That said, many modern EGT gauges do display absolute values, but as Ron said, what really counts is how many degrees above or below peak you are, not some absolute value.
Agree with posts regarding CHT. That's the important variable for cylinder longevity. (BTW, my club flies Archer III's with the same engine. 1480 is fine, but as stated, doesn't necessarily mean a lot. I would be more interested in the spread.) Unfortunately, you don't have CHT readout. That said, EGT readings can be of some use.
EGT is the result of the energy of combustion (energy released in the combustion of fuel/air) minus the energy used to produce horsepower or work, (including the energy used to heat the cylinder). Since an engine is not 100% efficient, the wasted energy flows out the tailpipe in the form of heat. If we lean an engine from full rich ( equates to a lot of unburned fuel) to best power, EGT will increase because the additional energy released in the fuel due to the more efficient burn is greater than the resultant increase in engine HP. If we lean from peak EGT to Lean Misfire, EGT will decrease because there is insufficient fuel in the fuel/air mixture, and thus less total energy. Given that mixture affects EGT, any problem with a cylinder's mixture, such as an intake leak, will impact EGT.
Using the "energy equation," as it relates to cylinder compression, a leaking cylinder (exhaust valve, rings, etc.) will also cause EGT to increase because the work output of the cylinder is less--less horsepower produced for the amount of fuel burned.
Even timing affects EGT. A retarded spark causes the peak pressure of combustion to occur later in the cycle and reduces horsepower, so EGT increases. (A misfiring plug, for example, will cause EGT to rise.)
A worn cam lobe will cause an intake valve not to fully open, thus allowing less fuel/air charge into the cylinder, resulting in a lower EGT.
So, as you can see, EGT output can be useful.
EGT is the result of the energy of combustion (energy released in the combustion of fuel/air) minus the energy used to produce horsepower or work, (including the energy used to heat the cylinder). Since an engine is not 100% efficient, the wasted energy flows out the tailpipe in the form of heat. If we lean an engine from full rich ( equates to a lot of unburned fuel) to best power, EGT will increase because the additional energy released in the fuel due to the more efficient burn is greater than the resultant increase in engine HP. If we lean from peak EGT to Lean Misfire, EGT will decrease because there is insufficient fuel in the fuel/air mixture, and thus less total energy. Given that mixture affects EGT, any problem with a cylinder's mixture, such as an intake leak, will impact EGT.
Using the "energy equation," as it relates to cylinder compression, a leaking cylinder (exhaust valve, rings, etc.) will also cause EGT to increase because the work output of the cylinder is less--less horsepower produced for the amount of fuel burned.
Even timing affects EGT. A retarded spark causes the peak pressure of combustion to occur later in the cycle and reduces horsepower, so EGT increases. (A misfiring plug, for example, will cause EGT to rise.)
A worn cam lobe will cause an intake valve not to fully open, thus allowing less fuel/air charge into the cylinder, resulting in a lower EGT.
So, as you can see, EGT output can be useful.
ntinkle
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As has been said, EGT spread can be dependent on several factors other than even fuel flows. The even fuel flow to each cylinder makes LOP possible/smooth. You typically want to be within .5 GPH spread from lowest to highest, although some engines can run sufficiently LOP with up to 1.1 or 1.2.
A lot of times, if you can't get far enough LOP on a carb engine, using carb heat will get you there.
ntinkle
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Here's an example of the spread in my SR22TN - EGT's 200 deg.s spread & CHT's 24 deg.s.
Following that is a GAMI spread - GPH for each cylinder - mine was .6. Goal was .5 or less, but ran very LOP just fine, so left it alone.
You can't be as precise with carbs, but thought they might alleviate some worry about large EGT spreads....
Following that is a GAMI spread - GPH for each cylinder - mine was .6. Goal was .5 or less, but ran very LOP just fine, so left it alone.
You can't be as precise with carbs, but thought they might alleviate some worry about large EGT spreads....
blueskyMD
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According to Lycoming Flyer spread of up to 150 d is acceptable. Here is the link
http://11hc.44rf.com/manuals/engine-prop/lycoming/lycoming---flyer_key_reprints.pdf
Download it. Good read for a new owner
http://11hc.44rf.com/manuals/engine-prop/lycoming/lycoming---flyer_key_reprints.pdf
Download it. Good read for a new owner