| [GMCnet] 4.8 MPG [message #324145] |
Thu, 21 September 2017 17:49  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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I would consider 15.5 to 16:1 too lean given the alcohol in today's gasoline and also think 13:1 under WOT is still not rich enough. I would be more comfortable if you were in the 12s under those conditions.
Stoichiometric (complete combustion) is a ratio of 14.7:1 only for unadulterated gasoline, not for this crap gas we have to use. Going 15.5 to 16 for any protracted period of time given the loads our coaches see could result in piston or valve damage, especially if spark goes away from the planned curve for any reason at the same time.
Where we live in Southern Oregon one needs to climb mountain passes in any direction. I drove up hill without ever allowing the vacuum to go below 4" (we sold both our GMCs so now have to write in past tense). If the grade was too steep to maintain 4" And 45 MPH I shifted down. That rarely happened with either coach and we took them all over North America from Alaska to Mexico and from the west coast to the Maritime Provences in eastern Canada.
I found that lightening up on the accelerator while going up hill did not reduce speed all that much but it sure improved vacuum and reduced the engine load. I think WOT for our engines under load with crap gas, or running too lean, or running too far advanced, is a recipe for bad stuff to happen. My experience, anyway.
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
http://jerrywork.com
........
Message: 3
Date: Thu, 21 Sep 2017 15:33:02 +0000
From: Keith V
To: "gmclist@list.gmcnet.org"
Subject: Re: [GMCnet] 4.8 MPG
Message-ID:
Content-Type: text/plain; charset="us-ascii"
So I got the 4.8 in an area with a lot of hills and I wasn't being nice to the coach, I was going up them at 60, same as on the flats.
On the way home I left the cruise off and let the speed sag on hills keeping the vacuum above 10, that got me above 8.
I have a wide band O2 that tells me I'm running 15.5-16.0 to 1 AFR, so it's not overly rich.
as I put the throttle down it richens up till it gets into the 13's at WOT
What do you do on hills to get an average of 8-9?
........i
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] 4.8 MPG [message #324161 is a reply to message #324145] |
Thu, 21 September 2017 20:32  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jerry,
Randy Van Winkle gave presentation at the Elkhart GMCMI Convention and noted that he runs his coach with EFI at that range
consistently.
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Gerald Work
Sent: Thursday, September 21, 2017 5:50 PM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] 4.8 MPG
I would consider 15.5 to 16:1 too lean given the alcohol in today's gasoline and also think 13:1 under WOT is still not rich enough.
I would be more comfortable if you were in the 12s under those conditions.
Stoichiometric (complete combustion) is a ratio of 14.7:1 only for unadulterated gasoline, not for this crap gas we have to use.
Going 15.5 to 16 for any protracted period of time given the loads our coaches see could result in piston or valve damage,
especially if spark goes away from the planned curve for any reason at the same time.
Where we live in Southern Oregon one needs to climb mountain passes in any direction. I drove up hill without ever allowing the
vacuum to go below 4" (we sold both our GMCs so now have to write in past tense). If the grade was too steep to maintain 4" And 45
MPH I shifted down. That rarely happened with either coach and we took them all over North America from Alaska to Mexico and from
the west coast to the Maritime Provences in eastern Canada.
I found that lightening up on the accelerator while going up hill did not reduce speed all that much but it sure improved vacuum and
reduced the engine load. I think WOT for our engines under load with crap gas, or running too lean, or running too far advanced, is
a recipe for bad stuff to happen. My experience, anyway.
Jerry Work
The Dovetail Joint
Fine furniture designed & hand crafted
in the 1907 former Masonic Temple building
in historic Kerby, OR
http://jerrywork.com
........
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Unsubscribe or Change List Options:
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] 4.8 MPG [message #324165 is a reply to message #324161] |
Thu, 21 September 2017 22:22 |
hal kading
Messages: 642
Registered: February 2004
Location: Las Cruces NM
Karma: 4
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Senior Member |
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Here's a good explanation of how to run lean without burning up your engine. You can cool the combustion with excess air or excess fuel. Note this only works at cruise power and with good control of the lean mixture.
<https://www.avweb.com/news/pelican/182084-1.html>
Hal Kading 78 Buskirk Las Cruces NM also with a 550 ci 300 hp powered aircraft that has been operated lean of peak egt at cruise for hundreds of hours.
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