EGT Monitoring, I searched all over.
07-07-2003, 04:28 PM
#1
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EGT Monitoring, I searched all over.
I am still confused on the process of monitoring EGT. What does the exhaust temperature tell you. I have seen tons of people say don't worry about A/F because any that you can afford are narrowband, so if you have no A/F sensor what does an EGT do for you? How do you know at what temperature you are running too lean? If anyone can give me any advice or direct me on where to go to read up on this it would be much appreciated.
Stephen
Stephen
07-07-2003, 05:25 PM
#3
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Yeah I understand that. But how do you determine which side of the lean-rich curve you are on. There is going to be a maximum A/F ratio in which the heat will be the highest. Then it will go down on either side. So how do you know which side you are on without having an A/F gauge. If anyone can explain the theory behind it rather than the practice it would help me out a lot.
THanks
Stephen
THanks
Stephen
07-08-2003, 08:58 AM
#5
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Yeah I understand the idea behind running rich. But seeing black smoke and lots of buildup at exhaust has nothing to do with the EGT gauge. I can figure out I am running rich without an EGT when there is buildup at exhaust. Sorry if I sound like a d*ck, but it doesn't seem as though everyone can give a practical reason for an EGT gauge, however everyone seems to say it is the first gauge you need.
Stephen
Stephen
07-08-2003, 10:38 AM
#6
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Join Date: Nov 2002
Location: San Diego
Posts: 1,780
Car Info: Boosted Geo Prizm
Yeah I understand that. But how do you determine which side of the lean-rich curve you are on.
Plain and simple stephen, you can't with just an EGT gauge alone. That is why you have to look at other factors to find out where you are running in terms of A/F. An EGT gauge is essential in terms of tuning and is especially helpful in regards to engine safety. What if you loaded a pre-made map from a so called "tuner," and it made your car run lean? Without an EGT gauge or an expensive wideband A/F setup you would never know.
You need to pick up a couple books on the subject and read up. Corky Bell's Maximum Boost is a good one. Also Engine Managment by Dave Walker, and four stroke performance tuning by A. Graham Bell.
goodbye.
07-15-2003, 11:24 AM
#7
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First of all, two things... 1) I may not have the chemistry terms down correctly, so bear with me all you chemistry freaks, and 2) I have not started tuning my WRX using engine management yet, so I can't offer any help at this piont. But, I will try my best to explain the practical use of an EGT guage.
I fly airplanes and you adjust the fuel mixture using an EGT guage all the time. Proper operation and longevity depends on it. Having your engine quit in a plane has much higher consequences than in a car.
EGT helps measure the efficiency of the combustion and how completely you are burning the fuel. Air / Fuel mixture is a ratio of oxygen molecules and fuel molecules. There is a stoichiometric ratio that is ideal (basically the right amount of gas versus the amount of air) that you will get a completely burned mixture and all the molucules will combine fully during combustion. One thing to note, though, is that the peak temperatures vary depending on certain conditions, like ambient temperature and pressure, octane and quality of the gas, etc. So, you can not tune for a particular EGT, because it is a relative figure. What was a peak EGT one day may not translate to the peak another day.
To use an EGT guage in a plane, basically you start with a rich mixture and note the EGT reading on the guage. As you lean the mixture, the temperature rises. You slowly start leaning the mixture until the needle stops climbing and you get a maximum EGT reading. This is called Peak EGT, and is a temperature reading at the probe measuring the exhaust gasses. Maximum EGT occurs when you have the best ratio of fuel and air. Keep in mind, though, that you have no safety margin when tuned to peak EGT. As you start leaning the mixture, you can notice the engine runs smoother and the RPMs increase as the EGT needle rises. At some point the needle stops rising as you continue to lean the mixture and then the temperature starts falling. You can notice the engine starting to not make as much power and the RPMs start falling. When you are at peak egt, your fuel consumption is at it's most efficient and your engine is making the best power under the given conditions (only taking mixture into account, of course).
If you continue to lean the mixture past Peak EGT, you will notice a drop in the EGT reading. This is due to the fact that you are not getting the most use of the oxygen because there are not enough fuel molecules to combine with all the oxygen molecules. Your EGT temp will go down, as well as your power output. This will also cause your engine's temperature (coolant temperature, block temp, and oil temp) to increase. This is because your engine depends on the cooling effect of the fuel entering into the cylinder (cooling effect from the differences in temperature between the cold fuel and the hot engine) and the cooling due to the evaporation of the fuel.
This can lead to detonation, which as you know is a bad thing.
So, you have to find a balance between producing the most power, using the fuel efficiently, and providing a safety margin. Typically, in a cruise setting where you are not at a high power output, say 60% to 75% of max power, I lean the mixture to peak EGT, then I enrichen the mixture to 50 degrees cooler than the peak reading. In a high power setting in which I am hammering the motor for extended periods of time, say 80% to 90% of max power, I lean to Peak EGT, then enrichen to 100 degrees on the cool side of Peak.
Hope this help.
I fly airplanes and you adjust the fuel mixture using an EGT guage all the time. Proper operation and longevity depends on it. Having your engine quit in a plane has much higher consequences than in a car.
EGT helps measure the efficiency of the combustion and how completely you are burning the fuel. Air / Fuel mixture is a ratio of oxygen molecules and fuel molecules. There is a stoichiometric ratio that is ideal (basically the right amount of gas versus the amount of air) that you will get a completely burned mixture and all the molucules will combine fully during combustion. One thing to note, though, is that the peak temperatures vary depending on certain conditions, like ambient temperature and pressure, octane and quality of the gas, etc. So, you can not tune for a particular EGT, because it is a relative figure. What was a peak EGT one day may not translate to the peak another day.
To use an EGT guage in a plane, basically you start with a rich mixture and note the EGT reading on the guage. As you lean the mixture, the temperature rises. You slowly start leaning the mixture until the needle stops climbing and you get a maximum EGT reading. This is called Peak EGT, and is a temperature reading at the probe measuring the exhaust gasses. Maximum EGT occurs when you have the best ratio of fuel and air. Keep in mind, though, that you have no safety margin when tuned to peak EGT. As you start leaning the mixture, you can notice the engine runs smoother and the RPMs increase as the EGT needle rises. At some point the needle stops rising as you continue to lean the mixture and then the temperature starts falling. You can notice the engine starting to not make as much power and the RPMs start falling. When you are at peak egt, your fuel consumption is at it's most efficient and your engine is making the best power under the given conditions (only taking mixture into account, of course).
If you continue to lean the mixture past Peak EGT, you will notice a drop in the EGT reading. This is due to the fact that you are not getting the most use of the oxygen because there are not enough fuel molecules to combine with all the oxygen molecules. Your EGT temp will go down, as well as your power output. This will also cause your engine's temperature (coolant temperature, block temp, and oil temp) to increase. This is because your engine depends on the cooling effect of the fuel entering into the cylinder (cooling effect from the differences in temperature between the cold fuel and the hot engine) and the cooling due to the evaporation of the fuel.
This can lead to detonation, which as you know is a bad thing.
So, you have to find a balance between producing the most power, using the fuel efficiently, and providing a safety margin. Typically, in a cruise setting where you are not at a high power output, say 60% to 75% of max power, I lean the mixture to peak EGT, then I enrichen the mixture to 50 degrees cooler than the peak reading. In a high power setting in which I am hammering the motor for extended periods of time, say 80% to 90% of max power, I lean to Peak EGT, then enrichen to 100 degrees on the cool side of Peak.
Hope this help.
07-15-2003, 01:06 PM
#8
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So basically unless you have the A/F gauge as well there is no use to the EGT gauge. Because it seems as though you would have to know the EGT based on settings as you said for the day. And hooking it up to a wideband A/F meter is not a practical thing to do everyday. If I am wrong in my thinking go ahead and correct me.
Stephen
Stephen
07-15-2003, 02:47 PM
#9
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The EGT doesnt actually change that much from day to day, I just want to be clear that looking for a certain value may be misleading, such as 400 degrees, every day, all day.
I think that you should be able to tune with the EGT by adjusting the fuel duty cycle (or how ever you control amount of fuel) and watch the effect on EGT. You can start rich then slowly reduce the amount of fuel for a given point on the map. You will be able to notice a change in the EGT. When it peaks and starts to go down, you know where the motor starts to go lean. You can then enrichen the mixture to drop the EGT to what ever value you are looking for. Just take good notes and watch the trends on th EGT. For x amount of fuel the EGT was y... and watch it go up (maybe even create a graph) so you know which side of the EGT curve you want to be on. You want to be on the RICH side of the curve, however many degrees (temperature- not angle) you are tuning for, not the lean side!
I think that you should be able to tune with the EGT by adjusting the fuel duty cycle (or how ever you control amount of fuel) and watch the effect on EGT. You can start rich then slowly reduce the amount of fuel for a given point on the map. You will be able to notice a change in the EGT. When it peaks and starts to go down, you know where the motor starts to go lean. You can then enrichen the mixture to drop the EGT to what ever value you are looking for. Just take good notes and watch the trends on th EGT. For x amount of fuel the EGT was y... and watch it go up (maybe even create a graph) so you know which side of the EGT curve you want to be on. You want to be on the RICH side of the curve, however many degrees (temperature- not angle) you are tuning for, not the lean side!
07-15-2003, 02:59 PM
#10
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One other thing, and maybe someone can correct me if I'm wrong...
Once you dial in the A/F ratio based on EGT, the ECU will automatically correct/compensate for temperature and pressure variations day in and day out. That's basically what the MAP, ambient temperature, and coolant temperature sensors feed into.
When you start modifying your A/F ratio, it is basically because you want to correct for two things; 1) the factory is trying to provide a safety margin in production cars for which they have to provide a warranty - so they tune on the rich side. 2) when you add cold air intakes, de-restrict the exhaust, etc, you are allowing more air into the engine for which the amount of fuel needs to be re-calibrated.
Once you re-calibrate the amount of fuel for a given throttle setting, load, and timing, you should pretty much be set. You should always monitor, don't get me wrong, but the daily tweaking should be at a minimum until you change something else.
Once you dial in the A/F ratio based on EGT, the ECU will automatically correct/compensate for temperature and pressure variations day in and day out. That's basically what the MAP, ambient temperature, and coolant temperature sensors feed into.
When you start modifying your A/F ratio, it is basically because you want to correct for two things; 1) the factory is trying to provide a safety margin in production cars for which they have to provide a warranty - so they tune on the rich side. 2) when you add cold air intakes, de-restrict the exhaust, etc, you are allowing more air into the engine for which the amount of fuel needs to be re-calibrated.
Once you re-calibrate the amount of fuel for a given throttle setting, load, and timing, you should pretty much be set. You should always monitor, don't get me wrong, but the daily tweaking should be at a minimum until you change something else.
