Which peak EGT should you use?

[Webb]

When I did my peak monitoring, I noticed that peak EGT temps went down slightly as altitude increased.

For the sake of aurgument, let's say cylinder #1 peaked at 1,400F at 8,000 feet. At 12,000 it peaked at 1,375.

If you want to run 50 LOP at 12,000 feet, should you run it at 1,325F or should you use the highest peak that was measured and run it at 1,350F?

Theoretically, at a higher altitudes peak EGT could be what at 8,000 was 50 degrees below peak. Should that peak temp be considered a static or dynamic number? If it is a static number then at any altitude above 8,000 feet, you would set the engine at a lean mixture setting where it runs best and the EGT did not exceed 1,350 degrees.

My reason for asking is from a metalurgical standpoint, the hottest peak EGT the engine would see at or above 8,000 feet would be 1,400 degrees.

[PCHunt]

......it's all relative!

The peak is the first cylinder to reach peak temp and begin cooling as you continue to lean the mixture.

Numbers mean nothing. The temp number is dependent on where the probe is placed, and your altitude, and your mixture, and.........

So, don't fret about numbers. When you level off at a cruising altitude, lean until the FIRST cylinder reaches peak EGT, whatever that number is. Then, either go 50 degrees ROP (old school), or continue leaning and run LOP.

They should remove numbers from the EGT gages. Or is it gauges? Only BuckWynd knows for sure!

[Webb]

Originally Posted by PCHunt

......it's all relative!

Numbers mean nothing. The temp number is dependent on where the probe is placed, and your altitude, and your mixture, and.........

The numbers were just an example....I may have put too much info. Remember the old dials with the moveable pointer......once you knew where peak was, you set it and left it alone.

ie: Do you run it at best mixture but don't exceed the 50F LOP measured at 8,000 feet no matter how much higher you go or do you use the peak for that altitude?

[plehrke]

Originally Posted by PCHunt

Then, either go 50 degrees ROP (old school), or continue leaning and run LOP.

Lycoming says that at 75% power and below it is OK to run at peak EGT for max economy. See page 37 section B 5 and page 42 paragraph 3. I get 0.5 gph better at peak then 50 deg ROP.
http://www.lycoming.textron.com/supp...Operations.pdf

[David-aviator]

Originally Posted by Webb

The numbers were just an example....I may have put too much info. Remember the old dials with the moveable pointer......once you knew where peak was, you set it and left it alone.

ie: Do you run it at best mixture but don't exceed the 50F LOP measured at 8,000 feet no matter how much higher you go or do you use the peak for that altitude?

Webb, we really don't know what a change in altitude (change in pressure and temperature) will do to the physics of a LOP setting at given altitude. It would be best to do it over when climbing or descending from that altitude.

In fact it may have to be reset at the original altitude if the flight transitions to an area of cooler or warmer temperatures. I once thought an engine was failing when the problem was much colder air, a slightly richer setting cured a rough running motor.

[Kevin Horton]

Originally Posted by Webb

When I did my peak monitoring, I noticed that peak EGT temps went down slightly as altitude increased.

For the sake of aurgument, let's say cylinder #1 peaked at 1,400F at 8,000 feet. At 12,000 it peaked at 1,375.

If you want to run 50 LOP at 12,000 feet, should you run it at 1,325F or should you use the highest peak that was measured and run it at 1,350F?

Peak EGT occurs at a specific fuel to air ratio. The whole point of running XX deg ROP or LOP is that they provide a reference to achieve fuel to air ratios that provide the desired power and internal cylinder pressures and temperatures that keep you away from detonation.

Bottom line - if you want to run XX deg ROP or LOP, you need to determine peak EGT at that altitude, OAT, rpm and MP. There is no point to using a peak EGT value that is from some other condition, as it has no bearing on the conditions your engine is seeing now. So, in the specific example you gave, if you want to cruise at 12,000 ft at 50 deg LOP, use the peak EGT value you found at 12,000 ft (1,375), and cruise at 1,325 deg EGT.

[frankh]

Originally Posted by PCHunt

......it's all relative!

The peak is the first cylinder to reach peak temp and begin cooling as you continue to lean the mixture.

Numbers mean nothing. The temp number is dependent on where the probe is placed, and your altitude, and your mixture, and.........

So, don't fret about numbers. When you level off at a cruising altitude, lean until the FIRST cylinder reaches peak EGT, whatever that number is. Then, either go 50 degrees ROP (old school), or continue leaning and run LOP.

!

The above is true if you want to run ROP..But is incorrect if you want to run LOP.

Assuming you are leaning from the rich side and you want to run LOP then it is the LAST cylinder to reach peak that you want to go from...If you take the first cylinder to hit peak and set that cylinder to be say 25F LOP, then one or more of the remaining cylinders could still be on the rich side, which may or may not be a problem depending on how much spread you have.

Much better to be safe and have all the cylinders on the lean side.

Frank

[Kahuna]

Originally Posted by frankh

The above is true if you want to run ROP..But is incorrect if you want to run LOP.

Assuming you are leaning from the rich side and you want to run LOP then it is the LAST cylinder to reach peak that you want to go from...If you take the first cylinder to hit peak and set that cylinder to be say 25F LOP, then one or more of the remaining cylinders could still be on the rich side, which may or may not be a problem depending on how much spread you have.

Much better to be safe and have all the cylinders on the lean side.

Frank

IF thats the case, then why does every engine monitor show the first to peak and not the last?

My opinion? It matters not. Folks ran engines for decades with the crude pull till its rough then richen. Basically running cylinders above and below peak in all conditions with long lifes. SO many engines with so many variables, they didnt fall out of the sky.

Todays monitors are finding the first. Works fine. If folks arent flow matched, they are doing themselves a diservice and making it harder on themselves.

[JonJay]

A little thread drift, but a chance lunch at Osh with a well respected LOP advocate convinced me that with our relatively low power, low compression, typical Lyco' or equivelant engines, properly timed, that detonation is not even possible, at any mixure or power setting.
I am in Kahuna's camp. Lean to roughness, or significant loss of power, enrichen slightly, whamo, you are LOP. My cylinders are well balanced, so they are all LOP. But, if detonation was inevitable, there would be a lot of blowing up going on that there is just no evidence of.
PS- My EMS has an LOP mode. It indicates first to peak but then switches to richest cylinder.

[breister]

I think Spock would say,

"Lean long, and prosper..."