Home » Public Forums » GMCnet » [GMCnet] Dreaming of overdrive
| [GMCnet] Dreaming of overdrive [message #219294] |
Tue, 20 August 2013 16:33  |
glwgmc
Messages: 1014
Registered: June 2004
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No matter how you do it, the key is to be able to run numerically higher gearing while under load (climbing a mountain) to reduce the internal stresses on the engine while also being able to run numerically lower gearing while not under load to increase fuel efficiency. With only three gears to select from it is really hard to do both with a 12,000 bread box going down the road. If the jumps between gears is too great, it won't work well and if the jumps are too small it won't be worth the effort. Just ask any bicyclist. The right combination is the gearing that will allow a nearly constant cadence going up hill, on the flat or going down hill. What changes is the speed/distance you travel. Same is true for our coaches. With a fourth gear available one can better match the gears to the available RPMs (cadence in the bicycle analogy) than one can do with only three gears available. If you were willing to put up with a top end of 50mph, it would be relatively easy to pr
operly gear for climbing mountains with just three speeds. But, since we seem to want a top end closer to 70mph three speeds are not enough except on relatively flat land unless you have the ability to generate a lot of torque and are willing to tolerate a lot of internal engine stress. Seems to me that our engine/transmission/final drive pairings have worked really well for 40 years and would only get better with a forth gear, no matter how we get there. My take anyway......
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
541-499-1027
541-592-5360
===============
Message: 16
Date: Tue, 20 Aug 2013 15:34:06 -0500
From: Glenn Giere <glenngiere@gmail.com>
Subject: Re: [GMCnet] Dreaming of overdrive
To: gmclist@temp.gmcnet.org
Message-ID: <3588c.5213d2be@gmc.mybirdfeeder.net>
Content-Type: text/plain; charset="ISO-8859-15"
I'm confused. What possible advantage would there be to overdrive? The right rear end ratio or addition of the power drive will put cruising RPM in the mid to upper 2000's, what more could you want?
Glenn
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Dreaming of overdrive [message #219370 is a reply to message #219294] |
Tue, 20 August 2013 23:40  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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The wind resistance, or drag makes for a not too great of an advantage.
Walt Halley and Tom Hampton did a trial run with a 2.89 type gears and
found any noticeable gain.
I think there is something there if we can still take advantage of some
factors that enter in.
On Tue, Aug 20, 2013 at 2:33 PM, Work Jerry <glwork@mac.com> wrote:
> No matter how you do it, the key is to be able to run numerically higher
> gearing while under load (climbing a mountain) to reduce the internal
> stresses on the engine while also being able to run numerically lower
> gearing while not under load to increase fuel efficiency. With only three
> gears to select from it is really hard to do both with a 12,000 bread box
> going down the road. If the jumps between gears is too great, it won't
> work well and if the jumps are too small it won't be worth the effort.
> Just ask any bicyclist. The right combination is the gearing that will
> allow a nearly constant cadence going up hill, on the flat or going down
> hill. What changes is the speed/distance you travel. Same is true for our
> coaches. With a fourth gear available one can better match the gears to
> the available RPMs (cadence in the bicycle analogy) than one can do with
> only three gears available. If you were willing to put up with a top end
> of 50mph, it would be relatively easy to pr
> operly gear for climbing mountains with just three speeds. But, since we
> seem to want a top end closer to 70mph three speeds are not enough except
> on relatively flat land unless you have the ability to generate a lot of
> torque and are willing to tolerate a lot of internal engine stress. Seems
> to me that our engine/transmission/final drive pairings have worked really
> well for 40 years and would only get better with a forth gear, no matter
> how we get there. My take anyway......
>
> Jerry
> Jerry Work
> The Dovetail Joint
> Fine furniture designed and hand crafted in the 1907 former Masonic Temple
> building in historic Kerby, OR
> Visitors always welcome!
> glwork@mac.com
> http://jerrywork.com
> 541-499-1027
> 541-592-5360
>
> ===============
>
> Message: 16
> Date: Tue, 20 Aug 2013 15:34:06 -0500
> From: Glenn Giere <glenngiere@gmail.com>
> Subject: Re: [GMCnet] Dreaming of overdrive
> To: gmclist@temp.gmcnet.org
> Message-ID: <3588c.5213d2be@gmc.mybirdfeeder.net>
> Content-Type: text/plain; charset="ISO-8859-15"
>
>
>
> I'm confused. What possible advantage would there be to overdrive? The
> right rear end ratio or addition of the power drive will put cruising RPM
> in the mid to upper 2000's, what more could you want?
>
> Glenn
> ============
>
>
> _______________________________________________
> 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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1-800-752-7502
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| Re: [GMCnet] Dreaming of overdrive [message #219371 is a reply to message #219294] |
Wed, 21 August 2013 00:29 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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F| glwgmc wrote on Tue, 20 August 2013 14:33 |
No matter how you do it, the key is to be able to run numerically higher gearing while under load (climbing a mountain) to reduce the internal stresses on the engine while also being able to run numerically lower gearing while not under load to increase fuel efficiency. With only three gears to select from it is really hard to do both with a 12,000 bread box going down the road. If the jumps between gears is too great, it won't work well and if the jumps are too small it won't be worth the effort. Just ask any bicyclist. The right combination is the gearing that will allow a nearly constant cadence going up hill, on the flat or going down hill. . Seems to me that our engine/transmission/final drive pairings have worked really well for 40 years and would only get better with a forth gear, no matter how we get there. My take anyway......
Jerry
Jerry Work
The Dovetail Joint
|
I agree with you, Jerry. There is a reason every car made for the past twenty years has an overdrive. On flat land you don't need RPMs.
We need to remember that a gas engine is not efficient at high vacuum. The reason it is economical is because the carburetor opens the power valve if the vacuum drops and the distributor retards the spark. Economical, but not efficient.
This is why diesel is more economical... No vacuum. No restriction in air. It takes energy to make that vacuum. The rod has to pull like crazy trying to pull the piston down against vacuum. Like trying to pull a syringe when the end is restricted.
When you are running down a hill in second gear, you are not "running against compression" you are running against vacuum. Shut off the fuel and open the throttle on a hill and you learn why diesels have exhaust brakes.
Plus, when the throttle is causing high vacuum, compression is low. There is just not as much air to compress. Less bang for your buck.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Dreaming of overdrive [message #219408 is a reply to message #219371] |
Wed, 21 August 2013 08:31 |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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Senior Member |
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And that is why I wonder if fuel injection could benefit from taller
gearing than a carb.
On Aug 20, 2013 10:29 PM, "George Beckman" <gbeckman@pggp.com> wrote:
>
>
> Fglwgmc wrote on Tue, 20 August 2013 14:33
> > No matter how you do it, the key is to be able to run numerically higher
> gearing while under load (climbing a mountain) to reduce the internal
> stresses on the engine while also being able to run numerically lower
> gearing while not under load to increase fuel efficiency. With only three
> gears to select from it is really hard to do both with a 12,000 bread box
> going down the road. If the jumps between gears is too great, it won't
> work well and if the jumps are too small it won't be worth the effort.
> Just ask any bicyclist. The right combination is the gearing that will
> allow a nearly constant cadence going up hill, on the flat or going down
> hill. . Seems to me that our engine/transmission/final drive pairings
> have worked really well for 40 years and would only get better with a forth
> gear, no matter how we get there. My take anyway......
> >
> > Jerry
> > Jerry Work
> > The Dovetail Joint
>
>
> I agree with you, Jerry. There is a reason every car made for the past
> twenty years has an overdrive. On flat land you don't need RPMs.
>
> We need to remember that a gas engine is not efficient at high vacuum. The
> reason it is economical is because the carburetor opens the power valve if
> the vacuum drops and the distributor retards the spark. Economical, but not
> efficient.
>
> This is why diesel is more economical... No vacuum. No restriction in air.
> It takes energy to make that vacuum. The rod has to pull like crazy trying
> to pull the piston down against vacuum. Like trying to pull a syringe when
> the end is restricted.
>
> When you are running down a hill in second gear, you are not "running
> against compression" you are running against vacuum. Shut off the fuel and
> open the throttle on a hill and you learn why diesels have exhaust brakes.
>
> Plus, when the throttle is causing high vacuum, compression is low. There
> is just not as much air to compress. Less bang for your buck.
> --
> '74 Eleganza, SE, Howell + EBL
> Best Wishes,
> George
> _______________________________________________
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1973 26' GM outfitted
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| Re: [GMCnet] Dreaming of overdrive [message #219722 is a reply to message #219294] |
Sat, 24 August 2013 11:12 |
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hnielsen2
Messages: 1434
Registered: February 2004
Location: Alpine CA
Karma: 0
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Senior Member |
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We have the Tac-Vac gauge
Try to keep the needles in the green and RPM at 3600 - 3800 for the best performances
That is our 455 sweet spot.
Not quite stock
With cam from Jim B,roller rockers,Mondello (sp?) push rods,Howell TBI ,double roller timing chain, 3:70 gears.
Howard
74 Canyon Lands
Hot Rod with Plumbing.
All is well with my Lord
Never Give Up
On Aug 24, 2013, at 8:32, James Hupy <jamesh1296@gmail.com> wrote:
> Ron, It is all related to throttle opening. If you can maintain momentum at
> 65 mph at 1/3 throttle opening, small rises in terrain pose no difficulty.
> But with taller gears, you have less mechanical advantage over increases in
> load, so more throttle opening is required to maintain pace. Wider throttle
> openings correlate to increased fuel consumption. Olds engines don't mind
> 3600 rpm all day long as long as the load is not too great. When an engine
> produces huge amounts of heat, (wide open throttle and heavy loads) is when
> engine life suffers. Jmho anyhow.
> Jim Hupy
> Salem, Or
> 78 GMC Royale 403 w/3:70 - 1 final drive.
> On Aug 24, 2013 8:20 AM, "Ronald Pottol" <ronaldpottol@gmail.com> wrote:
>
>> Ah, but a normal GMC seems to get the best milage with shorter than stock
>> gearing, 3.70 vs the stock 3.07.
>>
>> I keep thinking that with fuel injection, that should be the case, but I
>> have no data at all.
>> On Aug 24, 2013 8:05 AM, "Alan M DeLuccio" <delbassman@yahoo.com> wrote:
>>
>>>
>>>
>>> My thought is that having an overdrive on the GMC would basically give
>> you
>>> an additional gear. That way you could run higher final drive ratios that
>>> would help with towing, hill climbing, and passing, yet keep the
>> overdrive
>>> (4th) gear lower to get better freeway mileage. So, locking the torque
>>> converter would reduce slippage in 3rd gear, but hill climbing, passing,
>> &
>>> towing would remain the same?
>>> --
>>> AMDGMCMan
>>> Alan M DeLuccio
>>> 78 Royale with
>>> Coachmen,Center Kitchen Floorplan
>>> 09 Harley Davidson Street Glide
>>> 65 Corvair Monza Convertible
>>> 96 RAV4 2 door Manual 4WD
>>> Long Beach, CA
>>>
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| Re: [GMCnet] Dreaming of overdrive [message #219736 is a reply to message #219294] |
Sat, 24 August 2013 12:03 |
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hnielsen2
Messages: 1434
Registered: February 2004
Location: Alpine CA
Karma: 0
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Senior Member |
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I like our GMC the way it is.
Yes I did upgrade a little.
If I wanted some thing with all the bells and whistles I would go out and drop down $200,000,00 plus.
We have about $30,000 in our GMC that we will never recover.
Not a problem,
It's just the same with building Hot Rods.
The fun is in the building them and driving them.
You will never recover your $'s, but it beats hanging out at the local bar.
I belong to the local American Legion never go to the bar only the BBQ's.
I'm not a against drinking, I just don't have the time.
Got things to do and people to see.
Howard
Alpine Ca
All is well with my Lord
Never Give Up
On Aug 24, 2013, at 9:19, J A Holland <acts238bishop@yahoo.com> wrote:
>
>
> ~ O K, How About A 13 Speed Tranny,
> Jake Brakes
> And
> A Drivers Door While We're At It ? ~
>
> ~ Joe ~
> --
> /_]*[__][] *[__|] ~ * '73 TZE063V101887 ""
> O----------OO--]* ~ '78 TZE168V100234 ""
> " Joe & Lavelle " ""
> 'sweet home alebamy'
>
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