Home » Public Forums » GMCnet » Final Drives and MPG
| Final Drives and MPG [message #204810] |
Tue, 16 April 2013 12:37  |
Oldngray
Messages: 544
Registered: August 2009
Location: Punta Gorda Florida
Karma: 0
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Senior Member |
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Our FD is starting to make a little noise and assume it will just get louder, so am thinking about a replacement.
Is there a factual Analysis showing the best Engine/FD combination as it relates to MPG? If not, what parameters should be used to make a decision?
We have a 455/307 with Howell EBL/ESC and still do not get 9 MPG,
although it is much improved from the 6.5 to 7 that the Carb. gave us.
We seldom exceed 60 MPH or 2100 RPM. We do not Tow. Very little Hill climbing in Fl, Ga, and Al.
Thank you,
Richard
Richard MacDonald
Punta Gorda, Florida
Sold our TZE April 2015
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| Re: [GMCnet] Final Drives and MPG [message #204812 is a reply to message #204810] |
Tue, 16 April 2013 12:52  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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A little noise can sometimes go a long way before it gets to making
grinding and clunking sounds. It will take a very long time to cover the
cost of a lower geared final drive with a fuel savings of one mile per
gallon. That being said, for your use, I would think that the 3.55:1 ratio
would be nearly ideal with the 455 engine.
Jim Hupy
Salem, Or
78 Gmc Royale 403
On Apr 16, 2013 10:37 AM, "Richard MacDonald" <rm1936@gmail.com> wrote:
>
>
> Our FD is starting to make a little noise and assume it will just get
> louder, so am thinking about a replacement.
>
> Is there a factual Analysis showing the best Engine/FD combination as it
> relates to MPG? If not, what parameters should be used to make a decision?
>
> We have a 455/307 with Howell EBL/ESC and still do not get 9 MPG,
> although it is much improved from the 6.5 to 7 that the Carb. gave us.
> We seldom exceed 60 MPH or 2100 RPM. We do not Tow. Very little Hill
> climbing in Fl, Ga, and Al.
>
> Thank you,
> Richard
>
>
>
>
>
> --
> Richard MacDonald
> Punta Gorda, Florida
> 76 Edgemonte TZE 266V102313
> Howell TBI EBL
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Final Drives and MPG [message #204814 is a reply to message #204810] |
Tue, 16 April 2013 12:58 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Senior Member |
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Not sure if there is any scientific data out there. Here is our
experience......
We have the 403 engine and when we purchased the coach it had a 3:46 final
drive. Performance was good and mileage was about 8.9 mpg.
After I wrecked the final drive I replaced it with a 3:70, mileage improved,
performance is outstanding. As of last trip and fill the average was 9.3 mpg.
I typically run about 70 MPH on the highways.
Along with the 3:70 final drive we have the Patterson Ignition System and I've
had the Quadrajet carb rebuilt by Patterson.
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: Richard MacDonald <rm1936@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Tue, April 16, 2013 12:37:29 PM
Subject: [GMCnet] Final Drives and MPG
Our FD is starting to make a little noise and assume it will just get louder, so
am thinking about a replacement.
Is there a factual Analysis showing the best Engine/FD combination as it relates
to MPG? If not, what parameters should be used to make a decision?
We have a 455/307 with Howell EBL/ESC and still do not get 9 MPG,
although it is much improved from the 6.5 to 7 that the Carb. gave us.
We seldom exceed 60 MPH or 2100 RPM. We do not Tow. Very little Hill climbing in
Fl, Ga, and Al.
Thank you,
Richard
--
Richard MacDonald
Punta Gorda, Florida
76 Edgemonte TZE 266V102313
Howell TBI EBL
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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] Final Drives and MPG [message #204815 is a reply to message #204812] |
Tue, 16 April 2013 13:00 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Senior Member |
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I would agree with Jim. From all I've heard, with the 403 the 3:70 is the way
to go and with the 455 the 3:55 is great.
I wouldn't let a little noise bother me, you'll know without a doubt if it's
failing.
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: James Hupy <jamesh1296@gmail.com>
To: gmclist@temp.gmcnet.org
Sent: Tue, April 16, 2013 12:52:09 PM
Subject: Re: [GMCnet] Final Drives and MPG
A little noise can sometimes go a long way before it gets to making
grinding and clunking sounds. It will take a very long time to cover the
cost of a lower geared final drive with a fuel savings of one mile per
gallon. That being said, for your use, I would think that the 3.55:1 ratio
would be nearly ideal with the 455 engine.
Jim Hupy
Salem, Or
78 Gmc Royale 403
On Apr 16, 2013 10:37 AM, "Richard MacDonald" <rm1936@gmail.com> wrote:
>
>
> Our FD is starting to make a little noise and assume it will just get
> louder, so am thinking about a replacement.
>
> Is there a factual Analysis showing the best Engine/FD combination as it
> relates to MPG? If not, what parameters should be used to make a decision?
>
> We have a 455/307 with Howell EBL/ESC and still do not get 9 MPG,
> although it is much improved from the 6.5 to 7 that the Carb. gave us.
> We seldom exceed 60 MPH or 2100 RPM. We do not Tow. Very little Hill
> climbing in Fl, Ga, and Al.
>
> Thank you,
> Richard
>
>
>
>
>
> --
> Richard MacDonald
> Punta Gorda, Florida
> 76 Edgemonte TZE 266V102313
> Howell TBI EBL
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
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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: Final Drives and MPG [message #204841 is a reply to message #204810] |
Tue, 16 April 2013 15:34 |
Oldngray
Messages: 544
Registered: August 2009
Location: Punta Gorda Florida
Karma: 0
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Senior Member |
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Thanks Jim, Ray, I appreciate your replies.
Richard
Richard MacDonald
Punta Gorda, Florida
Sold our TZE April 2015
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| Re: [GMCnet] Final Drives and MPG [message #204844 is a reply to message #204810] |
Tue, 16 April 2013 16:01 |
Gary Berry
Messages: 1002
Registered: May 2005
Karma: -1
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Senior Member |
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Hey Richard;
I had a FD start making noise on me as I was north of Madras,OR (at
least that is when I first noticed it). I went to Bend, OR, got on the net,
and most everyone said to drive it to Applied GMC to get it fixed and that
it would make it there. I decided that since I had an extra 3:07 FD at home
(5 hours away) and that I was still 10 hours away from Applied GMC and that
this thing was howling like crazy that I would call my brother and see if
he would pick up the FD for me and drive it to Prineville, OR where I had a
friend that would let me use his driveway to do the R&R. I drove to
Prineville, and by the time my brother showed up we had the old FD pulled.
The pinion bearing was shot. Threw the other FD in and away I went. From
the time I noticed the whine until it started to howl was about 100 miles.
I later swapped the 3:07 for a 3:70. MPG didn't change, but it has been a
lot more fun going up hills.
--
Gary and Diana Berry
73 CL Stretch in Wa.
On Tue, Apr 16, 2013 at 10:37 AM, Richard MacDonald <rm1936@gmail.com>wrote:
>
> Our FD is starting to make a little noise and assume it will just get
> louder, so am thinking about a replacement.
> Thank you,
> Richard
>
>
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| Re: Final Drives and MPG [message #204845 is a reply to message #204810] |
Tue, 16 April 2013 16:18 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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| Oldngray wrote on Tue, 16 April 2013 10:37 |
Is there a factual Analysis showing the best Engine/FD combination as it relates to MPG? If not, what parameters should be used to make a decision?
We have a 455/307 with Howell EBL/ESC and still do not get 9 MPG,
although it is much improved from the 6.5 to 7 that the Carb. gave us.
We seldom exceed 60 MPH or 2100 RPM. We do not Tow. Very little Hill climbing in Fl, Ga, and Al.
Thank you,
Richard
|
As others have said, this is all conjecture, although after 40K miles in a GMC, some things become fairly evident.
One thing that might be happening here is the 2100 RPM. The Original stock torque converter had a stall of 2200 RPMs. (Lock the brakes and step on the gas and the RPMs go to 2200 with the coach not moving.) While torque converters without lockup clutches don't ever quit slipping, the stock unit is built to slip at 2100. You might try several tanks at 64 mph or so to see if this helps any. (I chose 64 because our coach really likes 64... everything seems to settle in.)
If you ever have to do a transmission, Manny's Switch Pitch will lower that stall to about 1600, unless in Switch which places it at about 2600. THe tighter torque converter is very responsive, even without lower gears. (Wouldn't want to try to maneuver into a steep camping site with it and a 3.07.) The last big trip I got 10.7 mpg, not towing. That was pump vs. actual miles traveled for 5400 miles. We were from CA to Washington to Montana to Canada to the Dakotas to Iowa and then home, so lots of variety. (Towing I seem to be more around 9.6, but I do it so seldom I only have 1200 miles experience since the switch pitch was installed.)
Also, with your EBL, do you have Vehicle Speed Sensor? The VSS allows the EBL to go into Highway Mode with is usually called Lean Cruise. The EBL will cut back on the air/fuel from 14.7:1 to 16.4:1 and at the same time advance the spark 4+ degrees. (These are according to settings but these are good averages.)
Each time our coach goes into Lean Cruise, the instant MPG goes up 1 MPG. VSS may be one of the cheaper items to help realize your mpg possibilities.
I believe with some more EBL tuning you will break the 10 mpg limit most of the time, regardless of the final drive.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: Final Drives and MPG [message #204868 is a reply to message #204845] |
Tue, 16 April 2013 19:09 |
Oldngray
Messages: 544
Registered: August 2009
Location: Punta Gorda Florida
Karma: 0
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Senior Member |
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Hi George, Do not understand what Stall, Slip, Tight etc means
when you speak of the Converter.
I have given some thought to VSS, just not sure what all is entailed to add it.
Richard
Richard MacDonald
Punta Gorda, Florida
Sold our TZE April 2015
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| Re: [GMCnet] Final Drives and MPG [message #204869 is a reply to message #204868] |
Tue, 16 April 2013 19:34 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Richard, the torque converter is a two part fluid coupling between the
engine and the transmission. Think of it like a clutch that is driven by
the engine, has fluid inside it, and when you spin the engine fast enough,
turns the input shaft to the transmission by the force of the fluid acting
upon the finned wheel attached to the input shaft. At a certain rpm, both
the engine and input shafts are turning nearly the same speed. That is
called converter lockup. Around 2400 rpm in the Gmc. If you run below the
lockup rpm, there is some disparity in the speed of the two shafts. This is
called slip. If it is great enough, fluid will heat excessively which is a
bad thing. Fuel economy is poorer when you have slippage as well. In
theory, if you run the engine at or above the lockup point, you should be
able to achieve better fuel economy. OPINIONS VARY WIDELY ON THIS POINT.
That is a thumbnail sketch of torque converters. Much more to it than what
I have talked about here.
Jim Hupy
Salem, Or
78 Gmc Royale 403 w/Manny Tranny and 3:70 - 1 final drive.p
On Apr 16, 2013 5:09 PM, "Richard MacDonald" <rm1936@gmail.com> wrote:
>
>
> Hi George, Do not understand what Stall, Slip, Tight etc means
> when you speak of the Converter.
> I have given some thought to VSS, just not sure what all is entailed to
> add it.
>
> Richard
> --
> Richard MacDonald
> Punta Gorda, Florida
> 76 Edgemonte TZE 266V102313
> Howell TBI EBL
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
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| Re: Final Drives and MPG [message #204886 is a reply to message #204810] |
Tue, 16 April 2013 22:08 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| Oldngray wrote on Tue, 16 April 2013 11:37 |
Our FD is starting to make a little noise and assume it will just get louder, so am thinking about a replacement.
Is there a factual Analysis showing the best Engine/FD combination as it relates to MPG? If not, what parameters should be used to make a decision?
We have a 455/307 with Howell EBL/ESC and still do not get 9 MPG,
although it is much improved from the 6.5 to 7 that the Carb. gave us.
We seldom exceed 60 MPH or 2100 RPM. We do not Tow. Very little Hill climbing in Fl, Ga, and Al.
Thank you,
Richard
Energy is energy so depending on where you drive, you want the engine to be in its prime area of efficiency.Higher speeds mean more friction and pumping losses, but I'm convinced that a tall final drive (3.07) and liberal use of 2cnd and 1 st works best for me in the mountains mixed with long flat runs at around 70 mph. It's not necessary nor benefical to be able to climb grades without downshifting. I suppose it's great for bragging rights but in the end it may be the wrong approach. We have great ratio coverage and it is greatest with a tall final drive. If you go to higher final drives, you are reducing your ratio coverage which I feel is the wrong thing to do. The higher (numerically) that you gear your coach, the less ratio spread and subsequently flexibility you have.
|
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Final Drives and MPG [message #204887 is a reply to message #204869] |
Tue, 16 April 2013 22:15 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| James Hupy wrote on Tue, 16 April 2013 18:34 |
Richard, the torque converter is a two part fluid coupling between the
engine and the transmission. Think of it like a clutch that is driven by
the engine, has fluid inside it, and when you spin the engine fast enough,
turns the input shaft to the transmission by the force of the fluid acting
upon the finned wheel attached to the input shaft. At a certain rpm, both
the engine and input shafts are turning nearly the same speed. That is
called converter lockup. Around 2400 rpm in the Gmc. If you run below the
lockup rpm, there is some disparity in the speed of the two shafts. This is
called slip. If it is great enough, fluid will heat excessively which is a
bad thing. Fuel economy is poorer when you have slippage as well. In
theory, if you run the engine at or above the lockup point, you should be
able to achieve better fuel economy. OPINIONS VARY WIDELY ON THIS POINT.
That is a thumbnail sketch of torque converters. Much more to it than what
I have talked about here.
Jim Hupy
Salem, Or
78 Gmc Royale 403 w/Manny Tranny and 3:70 - 1 final drive.p
On Apr 16, 2013 5:09 PM, "Richard MacDonald" <rm1936@gmail.com> wrote:
>
>
> Hi George, Do not understand what Stall, Slip, Tight etc means
> when you speak of the Converter.
> I have given some thought to VSS, just not sure what all is entailed to
> add it.
>
> Richard
> --
> Richard MacDonald
> Punta Gorda, Florida
> 76 Edgemonte TZE 266V102313
> Howell TBI EBL
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
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James, I have to disagree with you on this. Our stall(WOT engine and 0 output RPM) rpm is indeed around 2200 to 2400 rpm but the hydraulic lock-up point is much closer to 4000 rpm. Even at that rpm, we still have around 500 rpm slippage.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Final Drives and MPG [message #204892 is a reply to message #204887] |
Tue, 16 April 2013 22:53 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Jim Bounds drove the newly painted coach of Jim Decheine with 455 from
Orlando to Arizona and commented how well the 3.70 performed.
Up to this time, Jim B felt that 3.55 was the ideal ratio, but now he felt
that even small hills were not noticeable.
When we have over 3,000 units with 2,000 with3.70, we get feed back
constantly of power gain and no decrease in mileage.
We have over 50 with the 4.10 ratio that are pulling over 11mpg at 55-60
mph speed
On Tue, Apr 16, 2013 at 8:15 PM, Bob de Kruyff <NEXT2POOL@aol.com> wrote:
>
>
> James Hupy wrote on Tue, 16 April 2013 18:34
> > Richard, the torque converter is a two part fluid coupling between the
> > engine and the transmission. Think of it like a clutch that is driven by
> > the engine, has fluid inside it, and when you spin the engine fast
> enough,
> > turns the input shaft to the transmission by the force of the fluid
> acting
> > upon the finned wheel attached to the input shaft. At a certain rpm, both
> > the engine and input shafts are turning nearly the same speed. That is
> > called converter lockup. Around 2400 rpm in the Gmc. If you run below
> the
> > lockup rpm, there is some disparity in the speed of the two shafts. This
> is
> > called slip. If it is great enough, fluid will heat excessively which is
> a
> > bad thing. Fuel economy is poorer when you have slippage as well. In
> > theory, if you run the engine at or above the lockup point, you should be
> > able to achieve better fuel economy. OPINIONS VARY WIDELY ON THIS POINT.
> > That is a thumbnail sketch of torque converters. Much more to it than
> what
> > I have talked about here.
> > Jim Hupy
> > Salem, Or
> > 78 Gmc Royale 403 w/Manny Tranny and 3:70 - 1 final drive.p
> > On Apr 16, 2013 5:09 PM, "Richard MacDonald" <rm1936@gmail.com> wrote:
> >
> > >
> > >
> > > Hi George, Do not understand what Stall, Slip, Tight etc means
> > > when you speak of the Converter.
> > > I have given some thought to VSS, just not sure what all is entailed to
> > > add it.
> > >
> > > Richard
> > > --
> > > Richard MacDonald
> > > Punta Gorda, Florida
> > > 76 Edgemonte TZE 266V102313
> > > Howell TBI EBL
> > >
> > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> > >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> James, I have to disagree with you on this. Our stall(WOT engine and 0
> output RPM) rpm is indeed around 2200 to 2400 rpm but the hydraulic lock-up
> point is much closer to 4000 rpm. Even at that rpm, we still have around
> 500 rpm slippage.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Final Drives and MPG [message #204896 is a reply to message #204892] |
Tue, 16 April 2013 23:50 |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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Senior Member |
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I cannot argue with your data, but I'd love to understand why it is at such
variance with theory. I mean, in general, lower rpms should be more
efficient, but that isn't how it seems to be working out.
Any idea why?
Ron
On Apr 16, 2013 8:53 PM, "Jim Kanomata" <jimkanomata@gmail.com> wrote:
> Jim Bounds drove the newly painted coach of Jim Decheine with 455 from
> Orlando to Arizona and commented how well the 3.70 performed.
> Up to this time, Jim B felt that 3.55 was the ideal ratio, but now he felt
> that even small hills were not noticeable.
> When we have over 3,000 units with 2,000 with3.70, we get feed back
> constantly of power gain and no decrease in mileage.
> We have over 50 with the 4.10 ratio that are pulling over 11mpg at 55-60
> mph speed
>
> On Tue, Apr 16, 2013 at 8:15 PM, Bob de Kruyff <NEXT2POOL@aol.com> wrote:
>
> >
> >
> > James Hupy wrote on Tue, 16 April 2013 18:34
> > > Richard, the torque converter is a two part fluid coupling between the
> > > engine and the transmission. Think of it like a clutch that is driven
> by
> > > the engine, has fluid inside it, and when you spin the engine fast
> > enough,
> > > turns the input shaft to the transmission by the force of the fluid
> > acting
> > > upon the finned wheel attached to the input shaft. At a certain rpm,
> both
> > > the engine and input shafts are turning nearly the same speed. That is
> > > called converter lockup. Around 2400 rpm in the Gmc. If you run below
> > the
> > > lockup rpm, there is some disparity in the speed of the two shafts.
> This
> > is
> > > called slip. If it is great enough, fluid will heat excessively which
> is
> > a
> > > bad thing. Fuel economy is poorer when you have slippage as well. In
> > > theory, if you run the engine at or above the lockup point, you should
> be
> > > able to achieve better fuel economy. OPINIONS VARY WIDELY ON THIS
> POINT.
> > > That is a thumbnail sketch of torque converters. Much more to it than
> > what
> > > I have talked about here.
> > > Jim Hupy
> > > Salem, Or
> > > 78 Gmc Royale 403 w/Manny Tranny and 3:70 - 1 final drive.p
> > > On Apr 16, 2013 5:09 PM, "Richard MacDonald" <rm1936@gmail.com> wrote:
> > >
> > > >
> > > >
> > > > Hi George, Do not understand what Stall, Slip, Tight etc means
> > > > when you speak of the Converter.
> > > > I have given some thought to VSS, just not sure what all is entailed
> to
> > > > add it.
> > > >
> > > > Richard
> > > > --
> > > > Richard MacDonald
> > > > Punta Gorda, Florida
> > > > 76 Edgemonte TZE 266V102313
> > > > Howell TBI EBL
> > > >
> > > >
> > > > _______________________________________________
> > > > GMCnet mailing list
> > > > Unsubscribe or Change List Options:
> > > > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> > > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
> > James, I have to disagree with you on this. Our stall(WOT engine and 0
> > output RPM) rpm is indeed around 2200 to 2400 rpm but the hydraulic
> lock-up
> > point is much closer to 4000 rpm. Even at that rpm, we still have around
> > 500 rpm slippage.
> > --
> > Bob de Kruyff
> > 78 Eleganza
> > Chandler, AZ
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Fremont,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
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>
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1973 26' GM outfitted
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| Re: [GMCnet] Final Drives and MPG [message #204903 is a reply to message #204896] |
Wed, 17 April 2013 07:20 |
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mgrue
Messages: 192
Registered: October 2010
Location: Valmeyer IL
Karma: 0
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Senior Member |
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An engine (Really just a self powered air pump) will have an rpm at which it operates most efficiently. This RPM is dictated by valve sizes, intake and exauust port size and length piston dome shape, bore and stroke and several other factors. This RPM is usually not variable without physical engine work. Yes variable valve timing will change it but we don't need to worry about that with our engines. That RPM is normally the RPM at which the engine achives peak torque. I am not certain what it is on a 455 but I think it is around 2800 RPM on a stock engine. At that point the airflow is moving through the engine with the least losses and the parasitic losses are the lowest as a whole. It is also the RPM where the ignition and flame propagation in the cylinders is the best for that engine. In other words the fuel all gets burned before the exauust valve opens and the spent gasses are expelled just before the intake valve opens. If you can operate it at that RPM constantly you will get peak efficiency. The best way to do that is to match the transmission and final drive with the speed you are traveling. If you drive 60 you will need a lower final drive to keep the RPM up. If you drive 75 you will need a bit higher final drive to keep the RPM in the best efficiency range. On the 455 I seem to remember that range is fairly wide so a 3 speed transmission is ok for it. The trick is though to keep the torque converter turning fast enough to minimize slippage. That can be done by dropping a gear when you drive slower such as going up a hill but constant shifting down from 3rd to 2nd is hard on the transmission because of the way it changes gears... I know I have oversimplified this but bottom line keep the RPM in the "sweet spot" and mileage will improve. Final drive is the way to do that best with stock engine and transmission. Just my opinion though,
Mark
[quote title=Ronald Pottol wrote on Tue, 16 April 2013 23:50]I cannot argue with your data, but I'd love to understand why it is at such
variance with theory. I mean, in general, lower rpms should be more
efficient, but that isn't how it seems to be working out.
Any idea why?
Ron
On Apr 16, 2013 8:53 PM, "Jim Kanomata" <jimkanomata@gmail.com> wrote:
Mark Grueninger 76 Palm Beach
Valmeyer IL
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| Re: [GMCnet] Final Drives and MPG [message #204907 is a reply to message #204903] |
Wed, 17 April 2013 07:48 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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OK, a practical approach - I got to run up to STL in a couple of weeks, with the toadstone clipped on the coach. Going up Monteagle on I 24, the overflow bottle is boiling steam at the top. Am I better off to hang it in S at the bottom, and run it up at 2800 or so and whatever speed I get, as opposed to letting it downshift itself about halfway up? It's a 23' with the original 3:07 as far as I can tell - 62 per gets about 2250 or so on the tach, just under 2500 usually gives around 67 on the flat.
I don't like to see it get that hot, I'm toying with simply running West to Birmingspam and going that way, which skips the mountains entirely and gets a nice run up The Great River Road.
Thoughts?
--johnny
'76 23' transmode norris
'76 palm beach
________________________________
From: Mark Grueninger <markgrue@hotmail.com>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, April 17, 2013 8:20 AM
Subject: Re: [GMCnet] Final Drives and MPG
The best way to do that is to match the transmission and final drive with the speed you are traveling. If you drive 60 you will need a lower final drive to keep the RPM up. If you drive 75 you will need a bit higher final drive to keep the RPM in the best efficiency range. On the 455 I seem to remember that range is fairly wide so a 3 speed transmission is ok for it. The trick is though to keep the torque converter turning fast enough to minimize slippage. That can be done by dropping a gear when you drive slower such as going up a hill but constant shifting down from 3rd to 2nd is hard on the transmission because of the way it changes gears... I know I have oversimplified this but bottom line keep the RPM in the "sweet spot" and mileage will improve. Final drive is the way to do that best with stock engine and transmission. Just my opinion though,
Mark
[quote title=Ronald Pottol wrote on Tue, 16 April 2013 23:50]I cannot argue with your data, but I'd love to understand why it is at such
variance with theory. I mean, in general, lower rpms should be more
efficient, but that isn't how it seems to be working out.
Any idea why?
Ron
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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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| Re: [GMCnet] Final Drives and MPG [message #204935 is a reply to message #204887] |
Wed, 17 April 2013 10:56 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Bob, I had not noticed that you had been offnet until recently. Are you
still gainfully employed by U-haul or some such? When I noticed that you
were in disagreement with my ALL TOO SIMPLE explanation of torque
converters, it seemed like you had never been away.(grin) Every time I try
to offer a far too simple answer to complex problems you or Ken H or others
are quick to remind me of the HUGE BRAIN TRUST that exits in the GMC
community. I do know far more about torque converters than my simple answer
would indicate. I was trying to keep it simple. Should have known better
by now. Wait until next time!! (grin)
Jim Hupy
Salem, Or
78 Gmc Royale 403
On Apr 16, 2013 8:15 PM, "Bob de Kruyff" <NEXT2POOL@aol.com> wrote:
>
>
> James Hupy wrote on Tue, 16 April 2013 18:34
> > Richard, the torque converter is a two part fluid coupling between the
> > engine and the transmission. Think of it like a clutch that is driven by
> > the engine, has fluid inside it, and when you spin the engine fast
> enough,
> > turns the input shaft to the transmission by the force of the fluid
> acting
> > upon the finned wheel attached to the input shaft. At a certain rpm, both
> > the engine and input shafts are turning nearly the same speed. That is
> > called converter lockup. Around 2400 rpm in the Gmc. If you run below
> the
> > lockup rpm, there is some disparity in the speed of the two shafts. This
> is
> > called slip. If it is great enough, fluid will heat excessively which is
> a
> > bad thing. Fuel economy is poorer when you have slippage as well. In
> > theory, if you run the engine at or above the lockup point, you should be
> > able to achieve better fuel economy. OPINIONS VARY WIDELY ON THIS POINT.
> > That is a thumbnail sketch of torque converters. Much more to it than
> what
> > I have talked about here.
> > Jim Hupy
> > Salem, Or
> > 78 Gmc Royale 403 w/Manny Tranny and 3:70 - 1 final drive.p
> > On Apr 16, 2013 5:09 PM, "Richard MacDonald" <rm1936@gmail.com> wrote:
> >
> > >
> > >
> > > Hi George, Do not understand what Stall, Slip, Tight etc means
> > > when you speak of the Converter.
> > > I have given some thought to VSS, just not sure what all is entailed to
> > > add it.
> > >
> > > Richard
> > > --
> > > Richard MacDonald
> > > Punta Gorda, Florida
> > > 76 Edgemonte TZE 266V102313
> > > Howell TBI EBL
> > >
> > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> > >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> James, I have to disagree with you on this. Our stall(WOT engine and 0
> output RPM) rpm is indeed around 2200 to 2400 rpm but the hydraulic lock-up
> point is much closer to 4000 rpm. Even at that rpm, we still have around
> 500 rpm slippage.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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