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MHerder
Joined: 11 Feb 2008
Posts: 143
Location: Fort Worth TX
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 Posted: Mon Jan 24, 2011 7:15 am Post subject: EGT Spread Question-Rejetted |
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I just rejetted to a .250 main , and thing are running a lot smoother, no more soot, CHT’s are perfect, oilt temp perfect, and most of the EGT’s are with one being a little higher than the rest… Highest is 1325, lowest is 1190 or so with the other four in the middle. I’ve only run it rejetted for about an hour, so I wanted to check in with everyone and make sure I’m not hurting anything.
I’ve got about 7 hrs on the engine and granted it is cooler than normal here in Texas, but I’ve not had any CHT issues, or Oil Temperature issues. I followed the recommendations by Jabiru to the T regarding baffle design, ridges, the front gate etc. Maybe I’m just lucky? I was really anticipating having to fiddle with this, not that I’m disappointed.
A few questions:
At MWOT at level flight what is your EGT spread?
Which cylinder give you the hottest and coldest egt’s.
I understand that any disparity is most likely due to one cylinder getting more fuel than the others or less fuel for higher egt. I just want to find out what is realistically achievable with a carbureted engine.
Also, and most perplexing to me… I’ve been doing some reading on possible causes of high egt. One of the items that came up as a possibility was that one plug could be fouled. This is the exact opposite of what I thought would be the case. I thought if you would have a fouled plug, that the combustion might not be as complete and that the egt would be lower. Can someone please explain.
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BobsV35B(at)aol.com
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| Posted: Mon Jan 24, 2011 8:41 am Post subject: EGT Spread Question-Rejetted |
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Good Morning Mike,
When only one plug is firing, it takes longer for the burn to be completed. That means that the peak temperature occurs later in the cycle and closer to the time the exhaust valve opens giving you a higher reading on the EGT.
Brings home the point that we really should NOT worry about what the temperature actually is, we should evaluate EGT readings based on how they relate to some predetermined point.
You may recall that when Al Hundere, the fellow who popularized the use of an EGT gauge for us, made his first gauges available, they had no specific temperature on the gauge. We just had indices that were twenty-five degrees Fahrenheit apart. We were to find the peak temperature by careful leaning, then adjust the instrument so that the reading was at a little star place on the instrument. All further leaning or enrichment was based on the difference, either richer or leaner, than that peak EGT point.
Help at all?
Incidentally the name AlCor comes from Al's Corporation.
Happy Skies,
Old Bob
In a message dated 1/24/2011 9:19:22 A.M. Central Standard Time, michaelherder(at)beckgroup.com writes:
| Quote: | --> JabiruEngine-List message posted by: "MHerder" <michaelherder(at)beckgroup.com>
I just rejetted to a .250 main , and thing are running a lot smoother, no more soot, CHT’s are perfect, oilt temp perfect, and most of the EGT’s are with one being a little higher than the rest… Highest is 1325, lowest is 1190 or so with the other four in the middle. I’ve only run it rejetted for about an hour, so I wanted to check in with everyone and make sure I’m not hurting anything.
I’ve got about 7 hrs on the engine and granted it is cooler than normal here in Texas, but I’ve not had any CHT issues, or Oil Temperature issues. I followed the recommendations by Jabiru to the T regarding baffle design, ridges, the front gate etc. Maybe I’m just lucky? I was really anticipating having to fiddle with this, not that I’m disappointed.
A few questions:
At MWOT at level flight what is your EGT spread?
Which cylinder give you the hottest and coldest egt’s.
I understand that any disparity is most likely due to one cylinder getting more fuel than the others or less fuel for higher egt. I just want to find out what is realistically achievable with a carbureted engine.
Also, and most perplexing to me… I’ve been doing some reading on possible causes of high egt. One of the items that came up as a possibility was that one plug could be fouled. This is the exact opposite of what I thought would be the case. I thought if you would have a fouled plug, that the combustion might not be as complete and that the egt would be lower. Can someone please explain.
--------
One Rivet at a Time!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=328197#328197===============================================
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pete(at)usjabiru.com
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| Posted: Mon Jan 24, 2011 12:01 pm Post subject: EGT Spread Question-Rejetted |
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Old Bob’s analysis may apply to Lyc and Continental engines where the plugs are far apart and the flame in initiated from the top and bottom of the cylinder. Jabiru cylinders are smaller and the plugs are close together and the effect is hardly noticeable. I’ve flown on one mag and then switched to both and observed no difference in temps whatsoever and no difference in rpm. I’ve flown with one plug not firing (plug wire came off) and saw no differences in EGT and really only discovered that there was a problem when I did a mag check before shut down.
Pete
From: owner-jabiruengine-list-server(at)matronics.com [mailto:owner-jabiruengine-list-server(at)matronics.com] On Behalf Of BobsV35B(at)aol.com
Sent: Monday, January 24, 2011 10:32 AM
To: jabiruengine-list(at)matronics.com
Subject: Re: EGT Spread Question-Rejetted
Good Morning Mike,
When only one plug is firing, it takes longer for the burn to be completed. That means that the peak temperature occurs later in the cycle and closer to the time the exhaust valve opens giving you a higher reading on the EGT.
Brings home the point that we really should NOT worry about what the temperature actually is, we should evaluate EGT readings based on how they relate to some predetermined point.
You may recall that when Al Hundere, the fellow who popularized the use of an EGT gauge for us, made his first gauges available, they had no specific temperature on the gauge. We just had indices that were twenty-five degrees Fahrenheit apart. We were to find the peak temperature by careful leaning, then adjust the instrument so that the reading was at a little star place on the instrument. All further leaning or enrichment was based on the difference, either richer or leaner, than that peak EGT point.
Help at all?
Incidentally the name AlCor comes from Al's Corporation.
Happy Skies,
Old Bob
In a message dated 1/24/2011 9:19:22 A.M. Central Standard Time, michaelherder(at)beckgroup.com writes:
| Quote: |
--> JabiruEngine-List message posted by: "MHerder" <michaelherder(at)beckgroup.com>
I just rejetted to a .250 main , and thing are running a lot smoother, no more soot, CHT’s are perfect, oilt temp perfect, and most of the EGT’s are with one being a little higher than the rest… Highest is 1325, lowest is 1190 or so with the other four in the middle. I’ve only run it rejetted for about an hour, so I wanted to check in with everyone and make sure I’m not hurting anything.
I’ve got about 7 hrs on the engine and granted it is cooler than normal here in Texas, but I’ve not had any CHT issues, or Oil Temperature issues. I followed the recommendations by Jabiru to the T regarding baffle design, ridges, the front gate etc. Maybe I’m just lucky? I was really anticipating having to fiddle with this, not that I’m disappointed.
A few questions:
At MWOT at level flight what is your EGT spread?
Which cylinder give you the hottest and coldest egt’s.
I understand that any disparity is most likely due to one cylinder getting more fuel than the others or less fuel for higher egt. I just want to find out what is realistically achievable with a carbureted engine.
Also, and most perplexing to me… I’ve been doing some reading on possible causes of high egt. One of the items that came up as a possibility was that one plug could be fouled. This is the exact opposite of what I thought would be the case. I thought if you would have a fouled plug, that the combustion might not be as complete and that the egt would be lower. Can someone please explain.
--------
One Rivet at a Time!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=328197#328197=nbsp; = Use utilities Day ======================= - MATRONICS WEB FORUMS ======================= - List Contribution Web Site sp; = http://www.matronics.com/Navigator?JabiruEngine-List |
01234567
[quote][b]
| | - The Matronics JabiruEngine-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?JabiruEngine-List |
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BobsV35B(at)aol.com
Guest
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| Posted: Mon Jan 24, 2011 2:52 pm Post subject: EGT Spread Question-Rejetted |
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Good Afternoon Pete,
That sounds reasonable to me.
As Always, It All Depends! <G>
Happy Skies,
Old Bob
In a message dated 1/24/2011 2:01:34 P.M. Central Standard Time, pete(at)usjabiru.com writes:
| Quote: |
Old Bob’s analysis may apply to Lyc and Continental engines where the plugs are far apart and the flame in initiated from the top and bottom of the cylinder. Jabiru cylinders are smaller and the plugs are close together and the effect is hardly noticeable. I’ve flown on one mag and then switched to both and observed no difference in temps whatsoever and no difference in rpm. I’ve flown with one plug not firing (plug wire came off) and saw no differences in EGT and really only discovered that there was a problem when I did a mag check before shut down.
Pete
From: owner-jabiruengine-list-server(at)matronics.com [mailto:owner-jabiruengine-list-server(at)matronics.com] On Behalf Of BobsV35B(at)aol.com
Sent: Monday, January 24, 2011 10:32 AM
To: jabiruengine-list(at)matronics.com
Subject: Re: EGT Spread Question-Rejetted
Good Morning Mike,
When only one plug is firing, it takes longer for the burn to be completed. That means that the peak temperature occurs later in the cycle and closer to the time the exhaust valve opens giving you a higher reading on the EGT.
Brings home the point that we really should NOT worry about what the temperature actually is, we should evaluate EGT readings based on how they relate to some predetermined point.
You may recall that when Al Hundere, the fellow who popularized the use of an EGT gauge for us, made his first gauges available, they had no specific temperature on the gauge. We just had indices that were twenty-five degrees Fahrenheit apart. We were to find the peak temperature by careful leaning, then adjust the instrument so that the reading was at a little star place on the instrument. All further leaning or enrichment was based on the difference, either richer or leaner, than that peak EGT point.
Help at all?
Incidentally the name AlCor comes from Al's Corporation.
Happy Skies,
Old Bob
In a message dated 1/24/2011 9:19:22 A.M. Central Standard Time, michaelherder(at)beckgroup.com writes:
| Quote: |
--> JabiruEngine-List message posted by: "MHerder" <michaelherder(at)beckgroup.com>
I just rejetted to a .250 main , and thing are running a lot smoother, no more soot, CHT’s are perfect, oilt temp perfect, and most of the EGT’s are with one being a little higher than the rest… Highest is 1325, lowest is 1190 or so with the other four in the middle. I’ve only run it rejetted for about an hour, so I wanted to check in with everyone and make sure I’m not hurting anything.
I’ve got about 7 hrs on the engine and granted it is cooler than normal here in Texas, but I’ve not had any CHT issues, or Oil Temperature issues. I followed the recommendations by Jabiru to the T regarding baffle design, ridges, the front gate etc. Maybe I’m just lucky? I was really anticipating having to fiddle with this, not that I’m disappointed.
A few questions:
At MWOT at level flight what is your EGT spread?
Which cylinder give you the hottest and coldest egt’s.
I understand that any disparity is most likely due to one cylinder getting more fuel than the others or less fuel for higher egt. I just want to find out what is realistically achievable with a carbureted engine.
Also, and most perplexing to me… I’ve been doing some reading on possible causes of high egt. One of the items that came up as a possibility was that one plug could be fouled. This is the exact opposite of what I thought would be the case. I thought if you would have a fouled plug, that the combustion might not be as complete and that the egt would be lower. Can someone please explain.
--------
One Rivet at a Time!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=328197#328197=nbsp; = Use utilities Day ======================= - MATRONICS WEB FORUMS ======================= - List Contribution Web Site sp; = http://www.matronics.com/Navigator?JabiruEngine-List |
01234567
8 |
[quote][b]
| | - The Matronics JabiruEngine-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?JabiruEngine-List |
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