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Electronics international SR8 leaning


Tx_Aggie

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My ‘new to me’ M20J came with an electronics international sr8 engine monitor. It has 8 channels that are programmed for the four EGTs and the 4 chts. It was installed in 1988 and is still working well.

In a previous older model I flew, the owner told me as long the chts were below 380* everything will be good. Now that I own my one I really want to be efficient with my low time engine to get the best out of it and make it last. 

 The instruction manual says to press the ‘peak’ button and an arrow will display over the hottest cylinder as slow precise adjustments are made to the mixture. My question is, how do I know when I’ve reach peak before the engine starts to run rough? I appreciate it. 

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I don’t have an EI monitor, I have a JPI. But I am not sure about a couple of things in your question. You say the instruction manual says to press the peak button and an arrow will display over the hottest cylinder. Does “hottest cylinder” mean hottest CHT, or hottest EGT. It should be EGT for purposes of leaning out.

Assuming it is EGT, then does the unit stick with whichever cylinder it determines is the hottest? In other words, can you see EGT rise and then fall on that cylinder?  If you can, that is peak for that cylinder. If the system hops from one cylinder to the other as the hottest, then you are not going to get a very good peak reading. 

Assuming it sticks with just the one cylinder, then you want to see the temp rise and start to fall. That is “peak.” Now, if you are leaning Rich of Peak, you would enrich the mixture back in the direction you started about 125 dF would be a good number.

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Watch the EGT numbers. When they stop increasing and start going back down, you've peaked. The cylinder with the arrow over it should be the first one to peak--use that one if you fly ROP, and richen on up. For LOP, use the last cylinder to peak as your reference, and keep leaning. 

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1 hour ago, jlunseth said:

I don’t have an EI monitor, I have a JPI. But I am not sure about a couple of things in your question. You say the instruction manual says to press the peak button and an arrow will display over the hottest cylinder. Does “hottest cylinder” mean hottest CHT, or hottest EGT. It should be EGT for purposes of leaning out.

Assuming it is EGT, then does the unit stick with whichever cylinder it determines is the hottest? In other words, can you see EGT rise and then fall on that cylinder?  If you can, that is peak for that cylinder. If the system hops from one cylinder to the other as the hottest, then you are not going to get a very good peak reading. 

Assuming it sticks with just the one cylinder, then you want to see the temp rise and start to fall. That is “peak.” Now, if you are leaning Rich of Peak, you would enrich the mixture back in the direction you started about 125 dF would be a good number.

Exactly - I should have been a little more specific about seeking experience with those who have the EI engine scanner as the sequence is not as automatic as it is in the JPI. See the photo attached. Documentation from ~1988. 

IMG_2958.jpg

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2 hours ago, Tx_Aggie said:

Exactly - I should have been a little more specific about seeking experience with those who have the EI engine scanner as the sequence is not as automatic as it is in the JPI. See the photo attached. Documentation from ~1988. 

IMG_2958.jpg

Yep, that's EGT. You shouldn't try to lean by CHT, just make sure it stays cool. This is often done by reducing climb rate and / or slightly opening cowl flaps. 

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I think that is an old EI manual. It looks clear that when you press the Peak button, you are getting an EGT reading. It is not as clear whether the EI sticks with that cylinder, or hops around if another cylinder’s EGT becomes hotter. In other words, if it reads #2 as the hottest, then you start leaning towards peak, then #1’s EGT becomes hotter than #2’s, does it skip to #1. If it does that, it seems to me it has limited value  for leaning purposes. But if it picks a cylinder and sticks with that cylinder’s EGT, then it is somewhat useful.

Let’s say it fixes on a cylinder’s EGT and sticks with that one.  “Peak EGT” is what it sounds like, it is the point, when you pull the mixture back from a rich setting, where a cylinder’s EGT reaches its highest temperature and then starts to cool off as you pull the mixture further lean. So to translate that manual’s recommendations, what it is telling you to in the Rough Adjustment paragraph is to pull the mixture back until the engine runs rough. Generally, that means that your engine is running Lean of Peak. Then it tells you to make the mixture richer again until the engine smooths out, and leave it there to let the temps stabilize. So now you are operating at Peak or Rich of Peak. Once the temps have stabilized it then wants you to hit the Peak button and lean the mixture back until you find the hottest EGT. That is Peak EGT.  Then you would enrich the mixture again until the EGT is the desired number of degrees cooler than that peak temperature. The main purpose of the Rough Adjustment is what it says, it wants to get you operating the engine slightly rich of peak so when you activate the lean find (Peak) button, you don’t have very far to go to get to peak EGT.

Many POHs of older vintage did have many power settings for operating at peak EGT, and for mixtures where the temp is within 50 degrees of peak. That is what that paragraph B appears to be recommending.Those are not a very good place to operate the engine unless the engine is producing 65% power or less. I would try to get up around 100 degrees Rich of Peak EGT. Maybe some of the J guys can give you a better number. I have a turbo and our engines need a little more cushion from peak. It is generally understood that the range from Peak to 50 degrees Rich of Peak is a mixture setting that gives you the most heat and the highest Internal Cylinder Pressure spikes during combustion. It is hardest on the engine.

That would be a place to start. There is quite a bit more to understanding good engine management. You might go to www.gami.com and read through some of the articles, or read some of Mike Busch’s materials, then you will have a better understanding of it.

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Tx,

What you are missing... is the experience of leaning with an ancient instrument...

For any instrument used for leaning... you want to lean slowly as you get near peak... the engine hardware has its own lag time...

As in... make a change in mixture and see how long it takes for it to show on the instrument...
 

Then add to that... your instrument isn’t showing all four EGTs at the same time...

See if you can hold it on one cylinder while doing the leaning magic...

 

Then figure out which of the cylinders is always going to peak first... (almost always...)

 

For really good insight about EI instruments...  we have a really good EI guy around here...

 

This was a great scanning instrument back in the day...  there may be some used monitors that make more sense going forwards...
 

The aged historical manual is a fun read.... it is clear, yet Intentionally hides some detail... :)

Too bad they didn’t have MS back in the day...

Best regards,

-a-

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