Home » Public Forums » GMCnet » [GMCnet] Gas Mileage Test
| [GMCnet] Gas Mileage Test [message #218010] |
Mon, 12 August 2013 13:36  |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Senior Member |
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Good Afternoon
I know this subject gets talked about a lot, but I need to share my recent experience.
I have the 403 engine with a 3:70 final drive and Dick Pattersons rebuilt carb and his springfield iginition setup for my coach and for towing my trailer with the Harley in it, about 2,000 lbs for trailer and Harley.
My normal average gas mileage is right around 9 MPG since I put in the 3:70 final drive 3 years ago and I keep lunatic records.
This past week I took a trip up to Northern Wisconsin towing the trailer and Harley and decided to do a gas mileage test, since I had the whole day to travel there I decided to travel as close to 60-63 MPH as I could for the entire trip. I filled the tanks as full as I could get them and headed out, stayed at 60 nearly the entire time for 313 miles, then refilled the tanks to the same level.
RESULT: 7.53 MPG....... I thought...what the hell ?????
On the way home I decided to drive faster like I normally do and try to keep it at a consistent 70-73 MPH. Before I started out I filled the tanks again and traveled 353 miles home and then filled the tanks right to the top again.
RESULT: 9.78 MPG......
I don't have a tach or a vac gauge so I don't have that data.
Any ideas on what's going on here? Best I can figure is that the SWEET SPOT for my setup must be in the later higher speed & RPM range.
Comments or Thoughts???
The good ole GMC never fails to blow my mind and confuse me even more. These machines are weird !
Thanks
Ray
Ray & Lisa
78 Royale "Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMC-Royale@att.net
414-745-3188
Web Site: http://ray-lisa.page.tl/
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Ray Erspamer
78 GMC Royale Center Kitchen
403, 3.70 Final Drive
Holley Sniper Quadrajet EFI System,
Holley Hyperspark Ignition System
414-484-9431
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| Re: [GMCnet] Gas Mileage Test [message #218012 is a reply to message #218010] |
Mon, 12 August 2013 13:49  |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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well fill variations can easily explain that.
I just put 1700 miles on and kept running an average MPG logs.
The trip average was 9.4
trip hi was 13+
trip low was 7+
I am convinced that for the 13mpg run I underfilled the tank as the next run was the 7 mpg...
however I did notice that the coach sure seemed happier at 60+ than below 60.
Below 60 any little hill really bogged the engine.
above 60, the engine walked right up the hills.
this was watching the tach and vac gauge
tack reads 2500 at 60
Vac reads about 12
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] Gas Mileage Test [message #218032 is a reply to message #218026] |
Mon, 12 August 2013 15:45 |
stick miller
Messages: 1036
Registered: March 2010
Location: Americus, Georgia
Karma: 0
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I've never quite understood how mileage is determined. I'm pretty confident that each time mine is filled up it is to a different level. I've never run it out, so maybe that is the test. I just stop every 200-250 miles and get out a $100 bill.
Stick Miller
'78 Royale - "White Trash" - she left me for another man
'76 Eleganza - "Cousin Eddie" Sold
'84 Bluebird Wanderlodge - "Past Tents"
Americus, GA
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| Re: [GMCnet] Gas Mileage Test [message #218038 is a reply to message #218026] |
Mon, 12 August 2013 16:32 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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Ray: I`d try 80-83 and shoot for 12mpg.
| Jp Benson wrote on Mon, 12 August 2013 16:14 |
60-63 MPH - RESULT: 7.53 MPG....... I thought...what the hell ?????
70-73 MPH. - RESULT: 9.78 MPG......
Using the rule of thumb that aerodynamic drag is proportional to the square of the velocity then a 35% increase in wind drag nets 30% higher MPG. Maybe do a test run at 65-68 MPH.
JP
>________________________________
> From: Tim Conway <mactac735@mac.com>
>To: gmclist@temp.gmcnet.org
>Sent: Monday, August 12, 2013 2:55 PM
>Subject: Re: [GMCnet] Gas Mileage Test
>
>
>On Aug 12, 2013, at 2:36 PM, Ray Erspamer wrote:
>
>> Any ideas on what's going on here?
>
>Uphill and/or headwinds going, downhill and/or tailwinds coming?
>
>Tim Conway
>LI NY 78 PB
>
>_______________________________________________
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C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] Gas Mileage Test [message #218048 is a reply to message #218038] |
Mon, 12 August 2013 17:31 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Senior Member |
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Now this idea I like Charles.....but I think I'll go 100 to 103 and just get 18 MPG !
Ray
Ray & Lisa
78 Royale "Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMC-Royale@att.net
414-745-3188
Web Site: http://ray-lisa.page.tl/
________________________________
From: Charles Boyd <covered-wagon@comcast.net>
To: gmclist@temp.gmcnet.org
Sent: Monday, August 12, 2013 4:32 PM
Subject: Re: [GMCnet] Gas Mileage Test
Ray: I`d try 80-83 and shoot for 12mpg.
Jp Benson wrote on Mon, 12 August 2013 16:14
> 60-63 MPH - RESULT: 7.53 MPG....... I thought...what the hell ?????
>
> 70-73 MPH. - RESULT: 9.78 MPG......
>
>
> Using the rule of thumb that aerodynamic drag is proportional to the square of the velocity then a 35% increase in wind drag nets 30% higher MPG. Maybe do a test run at 65-68 MPH.
>
>
> JP
>
>
>
> >________________________________
> > From: Tim Conway <mactac735@mac.com>
> >To: gmclist@temp.gmcnet.org
> >Sent: Monday, August 12, 2013 2:55 PM
> >Subject: Re: [GMCnet] Gas Mileage Test
> >
> >
> >On Aug 12, 2013, at 2:36 PM, Ray Erspamer wrote:
> >
> >> Any ideas on what's going on here?
> >
> >Uphill and/or headwinds going, downhill and/or tailwinds coming?
> >
> >Tim Conway
> >LI NY 78 PB
> >
> >_______________________________________________
> >GMCnet mailing list
> >Unsubscribe or Change List Options:
> >http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
> >
> >
> _______________________________________________
> GMCnet mailing list
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--
C. Boyd
76 Crestmont
East Tennessee
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Ray Erspamer
78 GMC Royale Center Kitchen
403, 3.70 Final Drive
Holley Sniper Quadrajet EFI System,
Holley Hyperspark Ignition System
414-484-9431
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| Re: [GMCnet] Gas Mileage Test [message #218049 is a reply to message #218032] |
Mon, 12 August 2013 17:33 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Senior Member |
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We're doing the same run this weekend, I'll do another test, maybe go fast going UP and slower coming DOWN !
I would have expected the mileage coming back worse due to all of the Italian Food I ate up there !
Ray
Ray & Lisa
78 Royale "Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMC-Royale@att.net
414-745-3188
Web Site: http://ray-lisa.page.tl/
________________________________
From: Stick Miller <stickmiller@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Monday, August 12, 2013 3:45 PM
Subject: Re: [GMCnet] Gas Mileage Test
I've never quite understood how mileage is determined. I'm pretty confident that each time mine is filled up it is to a different level. I've never run it out, so maybe that is the test. I just stop every 200-250 miles and get out a $100 bill.
--
Stick Miller
'78 Royale - she left me for another man
'76 Eleganza
Americus, Georgia
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Ray Erspamer
78 GMC Royale Center Kitchen
403, 3.70 Final Drive
Holley Sniper Quadrajet EFI System,
Holley Hyperspark Ignition System
414-484-9431
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| Re: [GMCnet] Gas Mileage Test [message #218100 is a reply to message #218010] |
Tue, 13 August 2013 06:49 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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If I did the math right, about 41 gallons going and about 35 or so coming back. just over a ten percent improvement. I can vary the fill on my coach by 5 gallons and still get 'full' noted on the tanks, the last 3-4 gallons will take several minutes to get in the tanks. Consider that one of the fillups may well have had more alcohol in it than the other. That's good for nearly 10 percent. Maybeso more downhill one way than the other. So, this isn't a great concern.
I once got 12 going from Asheville to N Georgia - 55 mph freeway and downhill the whole way on real gasoline. Normally I see 9, bit over bobtailed, a bit under with the toad on. And while I'm not fanatic, I >do< have a cruddy notepad in the coach with the amount of gas, the mileage, and the <gasp!> cost of every time I('ve buought gat. Fill - to - fill, the mileage varies as much as 15%, indicating that I simply don't fill it the same every time. At some point when I'm bored I'll total up all the gas and miles and get a two year mileage average since I've had the thing. I'd expect it to be somewhat more accurate than a one - trip result. I've no intention of figuring out wwhat it cost.
--johnny
'76 23' transmode norris
'76 palm beach
--------------------------------------------
On Mon, 8/12/13, Ray Erspamer <78gmc-royale@att.net> wrote:
Subject: [GMCnet] Gas Mileage Test
To: "Net GMC" <gmclist@temp.gmcnet.org>
Date: Monday, August 12, 2013, 6:36 PM
Good Afternoon
I know this subject gets talked about a lot, but I need to
share my recent experience.
I have the 403 engine with a 3:70 final drive and Dick
Pattersons rebuilt carb and his springfield iginition setup
for my coach and for towing my trailer with the Harley in
it, about 2,000 lbs for trailer and Harley.
My normal average gas mileage is right around 9 MPG since I
put in the 3:70 final drive 3 years ago and I keep lunatic
records.
This past week I took a trip up to Northern Wisconsin towing
the trailer and Harley and decided to do a gas mileage test,
since I had the whole day to travel there I decided to
travel as close to 60-63 MPH as I could for the entire
trip. I filled the tanks as full as I could get them and
headed out, stayed at 60 nearly the entire time for 313
miles, then refilled the tanks to the same level.
RESULT: 7.53 MPG....... I thought...what the hell ?????
On the way home I decided to drive faster like I normally do
and try to keep it at a consistent 70-73 MPH. Before I
started out I filled the tanks again and traveled 353 miles
home and then filled the tanks right to the top again.
RESULT: 9.78 MPG......
I don't have a tach or a vac gauge so I don't have that
data.
Any ideas on what's going on here? Best I can figure is
that the SWEET SPOT for my setup must be in the later higher
speed & RPM range.
Comments or Thoughts???
The good ole GMC never fails to blow my mind and confuse me
even more. These machines are weird !
Thanks
Ray
Ray & Lisa
78 Royale "Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMC-Royale@att.net
414-745-3188
Web Site: http://ray-lisa.page.tl/
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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