Home » Public Forums » GMCnet » [GMCnet] Keeping it Real, 8 to 10 mpg
| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172575 is a reply to message #172554] |
Fri, 08 June 2012 10:53   |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
Karma: 0
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Guys who get 12mpg out of their GMCs keep us spending more money to try
and get that.
I figure with a 230 that I should be doing better than 8-10mpg. Then I
think about it more and realize I'm using old technology to drive a huge
wall into the wind. I tend to keep my speeds down compared to some. I
usually enjoy the driving experience in a GMC and am happy to be doing
62-63mph. It's positively relaxing compared to anything else I drive.
Maybe all these 12mpg GMCs are driving around in the Midwest on
dead-flat roads? We do have freeways that go up and down some here in
the Pacific NW.
Hopefully it's just guys bragging because they want to think they're
getting great mileage. FWIW, I see the same thing with the Datsun
crowd. Never saw more than 28mpg with any of my original-motored
Datsuns. Other guys swear they've seen 35mpg at 70mph. Ain't. Never.
Happened.
I'm positively anal about MPG. I can count on one hand the number of
times I haven't filled a tank (car or motorhome) and calculated MPG.
And always with "corrected" mileage. My GMC odo is almost perfectly
accurate but my car isn't.
I think Gene's "8-10mpg" is dead on. I should probably stop looking for
that 200mpg carburetor.
Kelvin
'73 23' in Eugene, OR
> During the four years we drove our 78 Royale I never saw more than 9.2
> mpg. In fact, the overall mileage for the coach (one AC on the roof and a
> pod, no tow) was 8.6. I would have enjoyed getting closer to 10. The only
> way to do that was to lie. I will say, also, that the best we got was when
> we happened to get some "real" gasoline in West Virginia in 2008. Ethanol,
> in my mind, gets the credit for reducing economy and performance (cough,
> cough).
>
> Byron Songer
>
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172584 is a reply to message #172575] |
Fri, 08 June 2012 12:13 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Maybe all these 12mpg GMCs are driving around in the Midwest on
dead-flat roads? We do have freeways that go up and down some here in
the Pacific NW.
Hopefully it's just guys bragging because they want to think they're
getting great mileage. FWIW, I see the same thing with the Datsun
crowd. Never saw more than 28mpg with any of my original-motored
Datsuns. Other guys swear they've seen 35mpg at 70mph. Ain't. Never.
Happened.
.
Right on Kelvin back in the day I had a friend that swore his 22 ft Kayot motor home got an honest 13 miles to the gallon. Well some time later my brother bought that 318 powered motor home and was he surprised when the actual mileage turned out to be 5 miles to the gallon.We wound up replacing the 2 barrel carburetor and manifold with a modified AFB four barrel and manifold as a rebuild on the 2 barrel was of no help. the 4 barrel increased it to 7 miles to the gallon. I have friends that tell me of big cars that get better mileage then my little Rav 4. When I check the manufactures estimated freeway MPG on those big cars it is 5-10 less? How can that be unless they are lying.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172641 is a reply to message #172628] |
Fri, 08 June 2012 18:46 |
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jaholland
Messages: 565
Registered: June 2010
Location: Sweet Home Alebamy
Karma: 0
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~~> I Got 15.6 MPG In The GMC Mountain Driving ! <~~
1978 Eleganza II 26 footer Motorhome
With 403 Engine
307 Final Drive
225-75R-16E Tires
Aluminum Performer Intake
Filled Ctossover
Thorley Headers /
3 Inch Exaust System
~~> " 15.6 MPG " <~~
This Jaw Dropping Fuel Mileage Was Calculated, Verified
And Recorded On Interstate I-77 Southbound While Driving
From Virginia To North Carolina @ 55 MPH -
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
according to my notes
We Filled Both Tanks At Fancy Gap Virginia
{ I-77 S - Exit 8 }
And
Re-Fueled Them At Mount Airy North Carolina
{ I-77 S - Exit 101 }
15.6 mpg Was The Best Fuel Mileage That I Ever Recorded ~
~ Joe ~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
BTW,
did I mention that 87 % of this drive
was coming down fancy gap mountain ?
/_]*[__][] *[__|] ~ * '73 TZE063V101887 "
"
O----------OO--]* ~ '78 TZE168V100234 "
"
" Joe & Lavelle " "
"
'sweet home alebamy'
[Updated on: Fri, 08 June 2012 18:52] Report message to a moderator |
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172646 is a reply to message #172628] |
Fri, 08 June 2012 20:03 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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G'day,
Many years ago when I was building hot rod Harleys over in Hong Kong I
worked with an old hot rodder named Jerry Branch. He was THE go to guy for
Harley heads.
We got to talking about the coefficient of drag (CoD) and how it affects
Harleys. He noted that every little gee-gaw (his words) hanging off the bike
into the air stream created turbulence and that he figgered running a stock
Harley down the road was like moving a 4 x 8 sheet of plywood through the
air stream.
A GMC doesn't have as much "stuff" hanging off the body shell but there's
enough to cause a fair amount of turbulence when one considers: the mirrors,
wind wings (if you installed them), roof A/C(s), TV antenna, satellite
antenna, Fantastic Fan vents, pods, luggage rail / ladder, etc.
I vaguely remembered that the CoD for the GMC was 0.3 something. I did a
Google search and found the following in the Wikipedia entry for GMC
Motorhome:
http://en.wikipedia.org/wiki/GMC_motorhome
GMC motorhomes in good condition and in proper tune are as efficient as
similarly powered modern motorhomes, despite the use of computer-controlled
engines on the latter, and typically see 9 to 11 miles per US gallon (21 to
26 L/100 km; 11 to 13 mpg-imp) of regular unleaded fuel. GMC Motorhomes
tested via a wind tunnel were reported to have a drag coefficient of 0.31,
which is typical of modern sedans (although offset by the large frontal
area).
I think Bill Bryant has the wind tunnel model and IIRC it is smooth as a
gut; NOTHING hanging off it.
At any rate I reckon that the CoD has a much greater effect on GMC mileage
than anything else.
Regards,
Rob "once again demonstrating an acute grasp on the obvious!" M.
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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] Keeping it Real, 8 to 10 mpg [message #172659 is a reply to message #172641] |
Fri, 08 June 2012 21:04 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Coming down the Mt with the Engine Off. Best mileage I ever got was 65 miles...used ZERO gas! Behind the tow truck last July!
Sent via BlackBerry by AT&T
-----Original Message-----
From: J A Holland <acts238bishop@yahoo.com>
Sender: gmclist-bounces@temp.gmcnet.org
Date: Fri, 08 Jun 2012 18:46:13
To: <gmclist@temp.gmcnet.org>
Reply-To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Keeping it Real, 8 to 10 mpg
1978 Eleganza II 26 footer Motorhome
With 403 Engine
307 Final Drive
225-75R-16E Tires
Aluminum Performer Intake
Filled Ctossover
Thorley Headers /
3 Inch Exaust System
~~> " 15.6 MPG " <~~
This Jaw Dropping Fuel Mileage Was Calculated, Verified
And Recorded On Interstate I-77 Southbound While Driving
From Virginia To North Carolina @ 55 MPH -
We Filled Both Tanks At Fancy Gap Virginia
{ I-77 S - Exit 8 }
And Re-Fueled At Mount Airy North Carolina
{ I-77 S - Exit 101 }
15.6 mpg Was The Best Fuel Mileage That I Ever Recorded ~
~ Joe ~
BTW,
did I mention that 87 % of this drive
was coming down fancy gap mountain ?
--
/_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
O----------OO--]* ~ '78 TZE168V100234 ""
" Joe & Lavelle " ""
'sweet home alebamy'
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GMCnet mailing list
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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] Keeping it Real, 8 to 10 mpg [message #172672 is a reply to message #172458] |
Fri, 08 June 2012 22:43 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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For the 100th Anniversary Chevy show at GM Detroit I had to drive a new tandem axle Peterbilt (new computer controled Diesel with DEF) from Chicago to Detroit loaded front to back and bottom to top. Heavy truck. Droped off at GM and drove home empty. The difference on the engine trip computer was .4 MPG better empty. It's mostly that fluid (air) you are pumping out of the way as you try to go down the road eating up the energy.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172699 is a reply to message #172646] |
Sat, 09 June 2012 10:57 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Robert Mueller wrote on Fri, 08 June 2012 18:03 |
...
A GMC doesn't have as much "stuff" hanging off the body shell but there's
enough to cause a fair amount of turbulence when one considers: the mirrors,
wind wings (if you installed them), roof A/C(s), TV antenna, satellite
antenna, Fantastic Fan vents, pods, luggage rail / ladder, etc. ...
|
Rob,
From what I understand, a small amount of turbulence actually REDUCES drag.... as long as it is in the right places. That is why golf balls have dimples.
There are people who make there living figuring out stuff like this... and I am not one of them! But to get an idea Google "vortex generators" and look for links that DO NOT have to do with aircraft.
Here is a link to a PDF from Mitsubishi motors... no I didn't read it, I looked at the pictures!
< http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&ved=0CJIBEBYwCg&url=http%3A%2F%2Fwww.mitsubishi-motors.com %2Fcorporate%2Fabout_us%2Ftechnology%2Freview%2Fe%2Fpdf%2F2004%2F16E_03.pdf&ei=aWvTT6PbPKre2AWxuY2kDw&usg=AFQjCNHArFCd4qeAHReUfG5fPxrlj7fL8w>
Anyway... From my prior readings, when bored... not from education or experience: With any shape, as long as you know what direction the airflow is coming from (like the front) you should be able to crate a small amount of turbulence where the pressures changes from high to low. This turbulence should form a boundary layer of air that expands (air does that) to make the shape seem "slipperier" to the air. Lowering drag.
But I MIGHT be full of something... like hot (turbulent) air!
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172700 is a reply to message #172699] |
Sat, 09 June 2012 11:01 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Mike Miller wrote on Sat, 09 June 2012 08:57 |
...From what I understand, a small amount of turbulence actually REDUCES drag....
... But I MIGHT be full of something... like hot (turbulent) air!
|
OBTW: At the speeds we use our GMC's at, I do not think vortex generators would really help MPG.
BUT they might add a MPH or two for a land speed record!
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172736 is a reply to message #172699] |
Sat, 09 June 2012 19:39 |
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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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Mike,
With all due respect I would suggest that you read the whole article (I did)
then readdress the subject.
I agree whole heartedly that vortex generators can reduce drag; HOWEVER,
they have to be designed and located properly.
I doubt that generating a vortex to reduce drag was taken into consideration
when any of the items mounted on the surface of a GMC I mentioned were
designed or located on a GMC.
I'd say at best some of them were designed to reduce their wind resistance,
however, I'd say the OEM mirrors sure flunked that design parameter. Plus
there isn't much you can do with a TV antenna or satellite dish and their
mechanisms to make them aerodynamic.
Regards,
Rob M.
-----Original Message-----
From: Mike Miller
Rob,
From what I understand, a small amount of turbulence actually REDUCES
drag.... as long as it is in the right places. That is why golf balls have
dimples.
There are people who make there living figuring out stuff like this... and I
am not one of them! But to get an idea Google "vortex generators" and look
for links that DO NOT have to do with aircraft.
Here is a link to a PDF from Mitsubishi motors... no I didn't read it, I
looked at the pictures!
<http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&ved=0CJIBEB
YwCg&url=http%3A%2F%2Fwww.mitsubishi-motors.com%2Fcorporate%2Fabout_us%2Ftec
hnology%2Freview%2Fe%2Fpdf%2F2004%2F16E_03.pdf&ei=aWvTT6PbPKre2AWxuY2kDw&usg
=AFQjCNHArFCd4qeAHReUfG5fPxrlj7fL8w>
Anyway... From my prior readings, when bored... not from education or
experience: With any shape, as long as you know what direction the airflow
is coming from (like the front) you should be able to crate a small amount
of turbulence where the pressures changes from high to low. This turbulence
should form a boundary layer of air that expands (air does that) to make the
shape seem "slipperier" to the air. Lowering drag.
But I MIGHT be full of something... like hot (turbulent) air!
--
Mike
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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] Keeping it Real, 8 to 10 mpg [message #172741 is a reply to message #172736] |
Sat, 09 June 2012 20:01 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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Senior Member |
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| Robert Mueller wrote on Sat, 09 June 2012 17:39 |
Mike,
With all due respect I would suggest that you read the whole article (I did)
then readdress the subject.
I agree whole heartedly that vortex generators can reduce drag; HOWEVER,
they have to be designed and located properly.
I doubt that generating a vortex to reduce drag was taken into consideration
when any of the items mounted on the surface of a GMC I mentioned were
designed or located on a GMC. ....
|
Agreed.
I never claimed anything attached to a GMC (OEM or not) created turbulence of the correct size, shape or location to help MPG or performance.
I was just trying to point out that not all turbulence was bad... even though most of it that we encounter is NOT helpful.
I do not need to go back and read the article... I pointed you at it and you read it for me! 
I had read a little on the subject in the past, when I had a bit of time. _IF_ I was interested in going for a land speed record, I would be collecting, reading and studying everything I could find on airflow characteristics... including vortex generators.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172749 is a reply to message #172741] |
Sat, 09 June 2012 20:49 |
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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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Mike,
My bad, I misinterpreted what you were saying.
I would love to go for the LSR but along with quite a few of my other dreams
$$$ required preclude them from making them real.
One comment though - I would use a fully equipped GMC motorhome, not a
gutted Transmode.
Regards,
Rob M.
-----Original Message-----
From: Mike Miller
Agreed.
I never claimed anything attached to a GMC (OEM or not) created turbulence
of the correct size, shape or location to help MPG or performance.
I was just trying to point out that not all turbulence was bad... even
though most of it that we encounter is NOT helpful.
I do not need to go back and read the article... I pointed you at it and you
read it for me! :twisted:
I had read a little on the subject in the past, when I had a bit of time.
_IF_ I was interested in going for a land speed record, I would be
collecting, reading and studying everything I could find on airflow
characteristics... including vortex generators.
--
Mike
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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] Keeping it Real, 8 to 10 mpg [message #172764 is a reply to message #172749] |
Sun, 10 June 2012 00:31 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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Senior Member |
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| Robert Mueller wrote on Sat, 09 June 2012 18:49 |
... One comment though - I would use a fully equipped GMC motorhome, not a gutted Transmode.
|
I agree that a MOTORHOME Land Speed Record should be held by a MOTORHOME.... not what amounts to an big empty van. Even if the "big van" has flames and a wing!
I saw something about someone oval track racing motorhomes. (Actually more of a demolition derby.) One of the requirements was that the driver had to spend the night before the race in the motorhome.
I know that sometimes (a lot of the time?) it is easy to "misinterpret" what I say.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Keeping it Real, 8 to 10 mpg [message #172766 is a reply to message #172764] |
Sun, 10 June 2012 01:52 |
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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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Mike,
That was on Top Gear, Richard Hammond starred in the episode:
http://www.youtube.com/watch?v=ohkAxbeMxVo
Regards,
Rob M.
-----Original Message-----
From: Mike Miller
I agree that a MOTORHOME Land Speed Record should be held by a MOTORHOME....
not what amounts to an big empty van. Even if the "big van" has flames and
a wing!
I saw something about someone oval track racing motorhomes. (Actually more
of a demolition derby.) One of the requirements was that the driver had to
spend the night before the race in the motorhome.
I know that sometimes (a lot of the time?) it is easy to "misinterpret" what
I say.
--
Mike
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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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