Home » Public Forums » GMCnet » [GMCnet] Final Drives
| [GMCnet] Final Drives [message #360385] |
Sun, 29 November 2020 21:30  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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Senior Member |
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I'll break my silence for this one. All trucks that had a GVW over 10,000 LBS back then. Had 3:70, 4:10, or 4:56 differentials. To reduce the load on the engine/trans. The GMC motor home was in the luxury group. They wanted to reduce sound in any way possible. Yes. There is a little more drivetrain sound. So, I added some extra sound barrier.
Now the sound is lower than with the 3:07. I treat our GMC like Apollo 13. Failure is NOT an option. I'm for increasing longevity. I personally rebuilt my trans in 2004. That same transmission is now in our present 78 Royale. With about 140,000 miles on its clock.18 years. Never been towed. 403 that is always pulling a GVW from 17,000 to 24,000 LBS GVW. Yes. Even in the mountains out West.
Reality is. You'll be running a higher vacuum. Thus, better mpg's. Plus, less load on the engine/trans. The engine will have more coolant going to the radiator. The trans will run cooler. Because there will be more trans fluid going to be cooled. That's what I have out here on the great plains. Love it.
I'll go back to my hole now. Hope that all of you have a better 2021. And remember. You can't tell those around you. That you love them too many times a day.
Bob Dunahugh
78 Royale sense 2003
4 COPO Yenkos, and way too many convertibles.
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| Re: [GMCnet] Final Drives [message #360389 is a reply to message #360385] |
Sun, 29 November 2020 22:16  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Bob,
You know your stuff as it shows on the products you supply on the
covair and others,
Appreciate your input.
No one will remind you to post with the original, but I will.
Thanks,
On Sun, Nov 29, 2020 at 7:31 PM Bob Dunahugh via Gmclist <
gmclist@list.gmcnet.org> wrote:
> I'll break my silence for this one. All trucks that had a GVW over
> 10,000 LBS back then. Had 3:70, 4:10, or 4:56 differentials. To reduce the
> load on the engine/trans. The GMC motor home was in the luxury group. They
> wanted to reduce sound in any way possible. Yes. There is a little more
> drivetrain sound. So, I added some extra sound barrier.
> Now the sound is lower than with the 3:07. I treat our GMC like Apollo
> 13. Failure is NOT an option. I'm for increasing longevity. I personally
> rebuilt my trans in 2004. That same transmission is now in our present 78
> Royale. With about 140,000 miles on its clock.18 years. Never been towed.
> 403 that is always pulling a GVW from 17,000 to 24,000 LBS GVW. Yes. Even
> in the mountains out West.
> Reality is. You'll be running a higher vacuum. Thus, better mpg's.
> Plus, less load on the engine/trans. The engine will have more coolant
> going to the radiator. The trans will run cooler. Because there will be
> more trans fluid going to be cooled. That's what I have out here on the
> great plains. Love it.
> I'll go back to my hole now. Hope that all of you have a better
> 2021. And remember. You can't tell those around you. That you love them too
> many times a day.
> Bob Dunahugh
> 78 Royale sense 2003
> 4 COPO Yenkos, and way too many convertibles.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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| Re: [GMCnet] Final Drives [message #360395 is a reply to message #360385] |
Mon, 30 November 2020 11:58 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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I just have to get on and write this.... I didn't want to start the topic on my own for reasons you may understand or not....
The 3.07 that was the original final drive in our coaches was wrong when they were built, but all the testing was done before the first Arab Oil Embargo. Speed limits were at least 70 everywhere and fuel cost was not a major issue. Then came 55 and all that went out the window. Even at 70, the 3.07 is a little low and GM knew that, but by the time they came up with the 3.42 number, nobody was interested.
Many people have been stuck for years with the long standing preconceived misconception that running an engine slower is always better. Better in terms of both fuel consumption and engine life. Well, both are wrong and for pretty much the same reasons.
Even in as little as the 50 years ago in my engine-engineering classes, we were taught two wrong things. One was that Piston-Miles were everything that mattered and conventional carburetor was mass-flow devices and so not subject to density issues. Well both were wrong.
At that time, piston miles was the primary engine wear determiner. Consumer Reports in their car data used to publish the N/V (that amounts to turns per mile.) Well, I hope to convince you that this is just wrong. A great deal of the engine wear is from internal friction. Most of that friction is directly related to the BMEP (Brake Mean Effective Pressure) that is what makes the torque that is needed to go down the road. Higher BMEP means more wear on the rings and bearings. People that have been around engines can tell you that lugging an engine is just bad for everything. Modern trucks are all geared with “Torque Backup”. They are geared so at most road conditions they are operating over the torque peak. This provides the reserve so they don’t lose speed and have to downshift for every little hill. This works well for us too.
First thing you have to wrap your thoughts around is that a more or less typical passcar has a road load of about 10~12Hp. I do not have numbers, but from decades of vehicle testing I would have to guess that the road load for 60~70MPH to be up there in the 30Hp region.
If you start up with a ~3K# passcar, with a ~100Hp engine, you have a very different situation than we do with a 10~12K# with an 250+Hp. Though that may sound equitable, you forgot the 30Hp road load we still have to manage. If that passcar engine is running below its torque peak, who cares? Just bump the throttle a little. If my coach is dragging on the hill and I bump the throttle, two things are happening. First is that the BMEP is going to climb putting more load on all the wearing parts. Then, the carburetor will probably move into the power enrichment part of its operation. There goes the fuel economy!
Ok, so what is the loss for spinning the crank faster? Pumping losses. An internal combustion engine is really just an air pump that burns fuel. As it happens the torque peak is closely associated with the peak Volumetric Efficiency (VE). When you spin it faster or slower, (with a fixed camshaft) that efficiency goes down. For an engine that is not set up for all out maximum power output, that curve can be relatively flat. That means that there is little penalty for spinning faster and, then there also is less wear on all the parts that you have to replace at some time.
Real fuel consumption is all in #/Hp-Hr. Notice that there is no element of crankshaft speed there. This will be on the engine map, and it will not be a straight line. It will have a little hump at the VE peak, but for engine like ours, that will not be any big issue.
Now we go back to the input side. I (personally) have to shift gears here because in engine labs we don’t have vacuum, we have manifold pressure. The two are inverse. I will try not to confuse these.
Whatever you fuel delivery control is, you want to deliver the minimum amount of fuel to create the horsepower you want. While the vacuum is high, there is not much charge in the cylinder, so not much heat is created even though the leaner mixtures actually burn hotter. Economy wise, this is all in your favor. But, when the vacuum gets lower and you have more charge in the cylinder that heat can be damaging, so the fuel system richens the mixture to keep the temperature in check. As backwards as this may seem to some, you would want to make road load horsepower with the vacuum as high as possible. That means that the engine is doing less work and making less friction all the way trough the driveline. That is a Win-Win for you.
Let’s take a minute to look at carburetors. This piece of nineteenth century technology survives even to this day because it is relatively simple and inexpensive to manufacture. It has been displaced because it is not known for its overall accuracy. Everything it does is a compromise. So, if you change air density, the calibration will probably not be ideal. Why does this matter in this discussion? Because the less manifold vacuum that the carburetor is seeing is also the most varying mass flow. That varying mass air flow means that the carburetor calibration will have a much harder time metering the fuel input. I would like to go into this more completely, but just to explain it adequately requires more time and mathematics than I have patience for right now. Suffice it to say that the steadier air flow of the higher vacuum will give better results.
I am going to break this off here because I have other things to do today. If there is some part of this where I lost you, please say so because you are probably not alone.
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Final Drives [message #360400 is a reply to message #360395] |
Mon, 30 November 2020 12:44 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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Senior Member |
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Great Stuff Matt,
I work with engineers, this is how like having things explained.
NOw can you turn all that into advice on final drive selection?
I can grasp that the engine is happier at higher revs even if i am not.
But my question remains, if 3.7 is great for a 26 footer with a big toad or a 403 then is a lower ratio optimal for a 23 footer that will not tow ?
And is the number 3.21 or something in the 3.5 range?
And is it foolish of me to want to cruise closer to 80 mph?
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: [GMCnet] Final Drives [message #360402 is a reply to message #360395] |
Mon, 30 November 2020 12:51 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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When I learned about VE ratios and RPM's per mile and BMEP was at Honda
motorcycle school. I had some preconceived beliefs about running engines
too slowly that were shaken up by Mr. HONDA'S brief quote "All other
factors being equal, rpm's are free." He went on to say that modern engine
design in air cooled motorcycle engines required waaayyy oversquare
configurations. That is where the bore is larger than the stroke, and more
small cylinders are better than fewer larger ones.
Examples were given to us in what was known as the Hailwood Sixes. Not
many of them existed, probably fewer than 100 were ever produced. None ever
ended up in privateer hands, they were exclusive to Honda Racing Division,
and factory riders. Mike Hailwood was one of them. Hence the nickname.
Those engines came "up on the cams" about 17,500 rpm, and redlined around
23,500 rpm. I had the opportunity to view those sixes in operation, they
made a sound all their own. More of a shrieking sound. The Yamaha 2 cycle
engines of the day were 2 cylinder and based on the RD street bike engines.
They realized about 9000 rpms and were prone to seizure if everything was
not perfect. On the starting grid, the 2 strokes were first off the start,
and that lasted until they ran out of rpms in first gear. At that point the
Hondas shot by them and just disappeared.
GMC application? The 403 is oversquare, the 455 is not. That is why
they like to rev, and the 455 likes to shake and not rev over 2900 or 3000.
Jim Hupy
Salem, Oregon
On Mon, Nov 30, 2020, 10:04 AM Matt Colie via Gmclist <
gmclist@list.gmcnet.org> wrote:
> I just have to get on and write this.... I didn't want to start the topic
> on my own for reasons you may understand or not....
>
> The 3.07 that was the original final drive in our coaches was wrong when
> they were built, but all the testing was done before the first Arab Oil
> Embargo. Speed limits were at least 70 everywhere and fuel cost was not a
> major issue. Then came 55 and all that went out the window. Even at 70,
> the 3.07 is a little low and GM knew that, but by the time they came up
> with the 3.42 number, nobody was interested.
>
> Many people have been stuck for years with the long standing preconceived
> misconception that running an engine slower is always better. Better in
> terms of both fuel consumption and engine life. Well, both are wrong and
> for pretty much the same reasons.
>
> Even in as little as the 50 years ago in my engine-engineering classes, we
> were taught two wrong things. One was that Piston-Miles were everything
> that mattered and conventional carburetor was mass-flow devices and so not
> subject to density issues. Well both were wrong.
>
> At that time, piston miles was the primary engine wear determiner.
> Consumer Reports in their car data used to publish the N/V (that amounts to
> turns
> per mile.) Well, I hope to convince you that this is just wrong. A great
> deal of the engine wear is from internal friction. Most of that friction
> is directly related to the BMEP (Brake Mean Effective Pressure) that is
> what makes the torque that is needed to go down the road. Higher BMEP means
> more wear on the rings and bearings. People that have been around engines
> can tell you that lugging an engine is just bad for everything. Modern
> trucks are all geared with “Torque Backup”. They are geared so at most
> road conditions they are operating over the torque peak. This provides
> the reserve so they don’t lose speed and have to downshift for every
> little hill. This works well for us too.
>
> First thing you have to wrap your thoughts around is that a more or less
> typical passcar has a road load of about 10~12Hp. I do not have numbers, but
> from decades of vehicle testing I would have to guess that the road load
> for 60~70MPH to be up there in the 30Hp region.
>
> If you start up with a ~3K# passcar, with a ~100Hp engine, you have a very
> different situation than we do with a 10~12K# with an 250+Hp. Though that
> may sound equitable, you forgot the 30Hp road load we still have to
> manage. If that passcar engine is running below its torque peak, who
> cares? Just
> bump the throttle a little. If my coach is dragging on the hill and I
> bump the throttle, two things are happening. First is that the BMEP is
> going
> to climb putting more load on all the wearing parts. Then, the carburetor
> will probably move into the power enrichment part of its operation. There
> goes the fuel economy!
>
> Ok, so what is the loss for spinning the crank faster? Pumping losses.
> An internal combustion engine is really just an air pump that burns fuel.
> As
> it happens the torque peak is closely associated with the peak Volumetric
> Efficiency (VE). When you spin it faster or slower, (with a fixed camshaft)
> that efficiency goes down. For an engine that is not set up for all out
> maximum power output, that curve can be relatively flat. That means that
> there is little penalty for spinning faster and, then there also is less
> wear on all the parts that you have to replace at some time.
>
> Real fuel consumption is all in #/Hp-Hr. Notice that there is no element
> of crankshaft speed there. This will be on the engine map, and it will not
> be a straight line. It will have a little hump at the VE peak, but for
> engine like ours, that will not be any big issue.
>
> Now we go back to the input side. I (personally) have to shift gears here
> because in engine labs we don’t have vacuum, we have manifold pressure.
> The two are inverse. I will try not to confuse these.
>
> Whatever you fuel delivery control is, you want to deliver the minimum
> amount of fuel to create the horsepower you want. While the vacuum is high,
> there is not much charge in the cylinder, so not much heat is created even
> though the leaner mixtures actually burn hotter. Economy wise, this is all
> in your favor. But, when the vacuum gets lower and you have more charge
> in the cylinder that heat can be damaging, so the fuel system richens the
> mixture to keep the temperature in check. As backwards as this may seem
> to some, you would want to make road load horsepower with the vacuum as high
> as possible. That means that the engine is doing less work and making
> less friction all the way trough the driveline. That is a Win-Win for you.
>
> Let’s take a minute to look at carburetors. This piece of nineteenth
> century technology survives even to this day because it is relatively simple
> and inexpensive to manufacture. It has been displaced because it is not
> known for its overall accuracy. Everything it does is a compromise. So, if
> you change air density, the calibration will probably not be ideal. Why
> does this matter in this discussion? Because the less manifold vacuum that
> the carburetor is seeing is also the most varying mass flow. That varying
> mass air flow means that the carburetor calibration will have a much harder
> time metering the fuel input. I would like to go into this more
> completely, but just to explain it adequately requires more time and
> mathematics than
> I have patience for right now. Suffice it to say that the steadier air
> flow of the higher vacuum will give better results.
>
> I am going to break this off here because I have other things to do
> today. If there is some part of this where I lost you, please say so
> because you
> are probably not alone.
> --
> Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL,
> GMCES
> Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum
> Brakes with Applied Control Arms
> SE Michigan - Near DTW - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] Final Drives [message #360403 is a reply to message #360400] |
Mon, 30 November 2020 13:01 |
|
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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hertfordnc wrote on Mon, 30 November 2020 13:44Great Stuff Matt,
I work with engineers, this is how like having things explained.
NOw can you turn all that into advice on final drive selection? = 1
I can grasp that the engine is happier at higher revs even if i am not.
But my question remains, if 3.7 is great for a 26 footer with a big toad or a 403 then is a lower ratio optimal for a 23 footer that will not tow ? = 2
And is the number 3.21 or something in the 3.5 range? = 3
And is it foolish of me to want to cruise closer to 80 mph? = 4
Dave,
Answers as best I can by numbers.
1 - You can us it as guidance
2 - If I had the spare cash, I would have put a 3.55 in my coach already.
3 - If there were other numbers available, I would have to consider them when I discovered them.
4 - That speed is closer to what the GMCs were built for, but Mary ran that speed on our way around Chicago one day and it resulted in amazingly high fuel rate. (We cruise at 60~65 and get ~9.2. That run was 7 and small change.)
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Final Drives [message #360404 is a reply to message #360400] |
Mon, 30 November 2020 13:12 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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I like the running over the torque peak idea, I have the 370
s on a fairly heavy royale, with the 307 it was a nightmare on the back roads I love to travel, 55mph and hilly was not fun.
Now with the 370s it just walks up the hills so nice.
the freeways are a breeze, it never strugles at all.
i would never put a lower ratio in, there is no point
________________________________
From: Gmclist on behalf of dave silva via Gmclist
Sent: Monday, November 30, 2020 12:44 PM
To: gmclist@list.gmcnet.org
Cc: dave silva
Subject: Re: [GMCnet] Final Drives
Great Stuff Matt,
I work with engineers, this is how like having things explained.
NOw can you turn all that into advice on final drive selection?
I can grasp that the engine is happier at higher revs even if i am not.
But my question remains, if 3.7 is great for a 26 footer with a big toad or a 403 then is a lower ratio optimal for a 23 footer that will not tow ?
And is the number 3.21 or something in the 3.5 range?
And is it foolish of me to want to cruise closer to 80 mph?
--
Dave & Ellen Silva
1972 Revcon Olds 455, toro drive train. All Stock
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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] Final Drives [message #360406 is a reply to message #360400] |
Mon, 30 November 2020 13:52 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Senior Member |
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Hey Dave:
Sound advice all the way around.
I like Strawberry. You might like chocolate. Or vanilla.
I cruise at 65 in the coach. All the time. Even in crosswinds. It’s a 455.
I’ve had a 3.70 and a 3.42
I’m going to put a 3.21 in. I don’t tow.
Mr. Honda’s observations are correct. RPM’s are free.
For me it was a balance of noise (creature comfort) and performance (more twist).
Strawberry.
Dolph
DE AD0LF
Wheeling, West Virginia
1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission
“The Aluminum and Fiberglass Mistress”
|[ ]~~~[][ ][] \
"--OO--[]---O-"
> On Nov 30, 2020, at 1:44 PM, dave silva via Gmclist wrote:
>
> Great Stuff Matt,
>
> I work with engineers, this is how like having things explained.
>
> NOw can you turn all that into advice on final drive selection?
>
> I can grasp that the engine is happier at higher revs even if i am not.
>
> But my question remains, if 3.7 is great for a 26 footer with a big toad or a 403 then is a lower ratio optimal for a 23 footer that will not tow ?
>
> And is the number 3.21 or something in the 3.5 range?
>
> And is it foolish of me to want to cruise closer to 80 mph?
>
>
>
>
> --
> Dave & Ellen Silva
>
> 1972 Revcon Olds 455, toro drive train. All Stock
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Final Drives [message #360408 is a reply to message #360406] |
Mon, 30 November 2020 15:25 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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I can tell you for sure , your mileage
does not go down with 3.70 .
Look at what the vacuum gage reads., higher, less fuel dispensed.
If you know anything about what that does to milage, it always proves out
unless your distributor and or Carb is mal functioning.,
On Mon, Nov 30, 2020 at 11:53 AM Dolph Santorine via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Hey Dave:
>
> Sound advice all the way around.
>
> I like Strawberry. You might like chocolate. Or vanilla.
>
> I cruise at 65 in the coach. All the time. Even in crosswinds. It’s a 455.
>
> I’ve had a 3.70 and a 3.42
>
> I’m going to put a 3.21 in. I don’t tow.
>
> Mr. Honda’s observations are correct. RPM’s are free.
>
> For me it was a balance of noise (creature comfort) and performance (more
> twist).
>
> Strawberry.
>
> Dolph
>
> DE AD0LF
>
> Wheeling, West Virginia
>
> 1977 26’ ex-PalmBeach
> Howell EFI & EBL, Reaction Arms, Manny Transmission
>
> “The Aluminum and Fiberglass Mistress”
>
> |[ ]~~~[][ ][] \
> "--OO--[]---O-"
>
>> On Nov 30, 2020, at 1:44 PM, dave silva via Gmclist gmclist@list.gmcnet.org> wrote:
>>
>> Great Stuff Matt,
>>
>> I work with engineers, this is how like having things explained.
>>
>> NOw can you turn all that into advice on final drive selection?
>>
>> I can grasp that the engine is happier at higher revs even if i am not.
>>
>> But my question remains, if 3.7 is great for a 26 footer with a big toad
> or a 403 then is a lower ratio optimal for a 23 footer that will not tow ?
>>
>> And is the number 3.21 or something in the 3.5 range?
>>
>> And is it foolish of me to want to cruise closer to 80 mph?
>>
>>
>>
>>
>> --
>> Dave & Ellen Silva
>>
>> 1972 Revcon Olds 455, toro drive train. All Stock
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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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 [message #360415 is a reply to message #360412] |
Mon, 30 November 2020 17:24 |
Rob
Messages: 651
Registered: November 2013
Location: Victoria, BC
Karma: 3
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Senior Member |
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I really like my 3.55 - but sometimes think 3.70 would be nice. Limited slip would be GREAT.
But I tend to drive it like it's stolen.
Rob
76 Royale Twin Beds, Dry Bath
Victoria, BC
> On Nov 30, 2020, at 3:03 PM, Steve Weinstock via Gmclist wrote:
>
> EXCELLENT discussion...
>
> I have a 1973 23 footer with a 455 and a 3.70 (limited slip). And a Manny transmission. I occasionally tow a Suzuki X-90.
>
> 2800- 3000 rpm on the freeway at somewhere around 60 mph.
>
> I’ve always wondered if I’m over geared - but it sure goes up hills pretty darn good.
>
> I’d like to try a 3.55 sometime...
>
> Thanks to our gurus for all of their contributions to this site. I’ve certainly been a beneficiary.
>
> Steve W
>
>
>
>
>
>
> --
> Steve W
> 1973 : 23'
> Southern California
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Rob -
Victoria, BC -
76 Royale - Rear Twins/Dry Bath
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| Re: [GMCnet] Final Drives [message #360421 is a reply to message #360415] |
Mon, 30 November 2020 19:31 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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a 370 with limited slip IS great!
________________________________
From: Gmclist on behalf of Rob via Gmclist
Sent: Monday, November 30, 2020 5:24 PM
To: gmclist@list.gmcnet.org
Cc: Rob
Subject: Re: [GMCnet] Final Drives
I really like my 3.55 - but sometimes think 3.70 would be nice. Limited slip would be GREAT.
But I tend to drive it like it's stolen.
Rob
76 Royale Twin Beds, Dry Bath
Victoria, BC
> On Nov 30, 2020, at 3:03 PM, Steve Weinstock via Gmclist wrote:
>
> EXCELLENT discussion...
>
> I have a 1973 23 footer with a 455 and a 3.70 (limited slip). And a Manny transmission. I occasionally tow a Suzuki X-90.
>
> 2800- 3000 rpm on the freeway at somewhere around 60 mph.
>
> I’ve always wondered if I’m over geared - but it sure goes up hills pretty darn good.
>
> I’d like to try a 3.55 sometime...
>
> Thanks to our gurus for all of their contributions to this site. I’ve certainly been a beneficiary.
>
> Steve W
>
>
>
>
>
>
> --
> Steve W
> 1973 : 23'
> Southern California
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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] Final Drives [message #360422 is a reply to message #360400] |
Mon, 30 November 2020 21:31 |
tmsnyder
Messages: 151
Registered: January 2014
Karma: -9
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Senior Member |
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Another possibly inexpensive (free) way to think about this. Stock from the factory it came with an available 4.54 final drive ratio built in. It's called 2nd gear (or Super gear according to the manual and the shift indicator LOL)
If you never venture over 60 mph this is the perfect gear. 60mph is 3128 rpm in Super according to my calcs on stock tires.
55 mph is 2868 RPM in Super. That seems like it would be a really comfortable engine speed to travel at especially on local roads.
Currently I have a 3.50 in mine (not installed by me, but based on the gps indicated speed and tach reading) and it loves to roll along at 72 or so, happily singing along at 2800 RPM. Actually it keeps creeping up on me, I'll look down and be over 75mph without realizing it. It really seems to be happiest at about 3000 rpm which shouldn't be a surprise, that where gas engines were typically designed to run back in the day.
In the owners' manual it reads:
"SUPER RANGE "S"-Used when super performance is needed for increased acceleration
in traffic, hill climbing, or "Engine Braking"
down-hill. The selector lever may be moved
from "D" to "S" and vice versa, under most
operating conditions. "SUPER" should not
be used at speeds above 75 MPH."
It also reads:
"When additional
acceleration is desired to pass moving vehicles or to climb steep grades at speeds
between approximately 35 and 65 MPH, the
transmission can be downshifted by depressing the accelerator pedal completely to the
floor"
According to my spreadsheet:
75mph in 2nd will result in 3910rpm (too beaucoup)
65mph in 2nd will result in 3390rpm (ok briefly but too beaucoup for very long)
60mph: 3128rpm (a little high)
55mph: 2868rpm (a very happy spot)
Just something to think about, if you're towing something and/or never get over 55-60mph, maybe consider just leaving it in Super. There's something to be said for slowing down and enjoying the drive and the scenery out the front windshield.
Cheers
Todd in Buffalo, NY
Todd Snyder, Buffalo NY
1976 Eleganza II
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| Re: [GMCnet] Final Drives [message #360430 is a reply to message #360428] |
Tue, 01 December 2020 10:31 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Mark, that audio made my morning! Thanks for the trip down memory lane.
Great stuff.
Jim Hupy
Salem, Oregon
On Tue, Dec 1, 2020, 7:38 AM Mark Sawyer via Gmclist <
gmclist@list.gmcnet.org> wrote:
> 1967 Isle of Mann TT - Honda Hailwood Six:
>
>
> https://www.visordown.com/reviews/product/audio-hailwood-honda-six-full-song
>
> Sound of their own, indeed....
>
>
> --
> Mark S. '73 Painted Desert,
> Manny 1 Ton Front End,
> Howell Injection,
> Leigh Harrison 4bag and Rear Brakes,
> Fort Worth, TX
>
> _______________________________________________
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| Re: [GMCnet] Final Drives [message #360432 is a reply to message #360385] |
Tue, 01 December 2020 11:19 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Drive it like you stole it, usually refers to driving it fast and hard with
total disregard for anything like mechanical damage. Kinda like Mario
Andretti in the early part of his driving career. He broke a lot of race
cars, before he learned that in order to win, you have to finish the race,
too. That meant turning that boost control on the turbos down and lifting
your foot off the firewall a little bit.
Jim Hupy
Salem, Oregon
On Tue, Dec 1, 2020, 9:06 AM Emery Stora via Gmclist <
gmclist@list.gmcnet.org> wrote:
> I’ve never been sure what “I drive it like it’s stolen” means. Does that
> mean you drive carefully within the speed limit so you hopefully won’t be
> pulled over or does it mean you drive as fast as hell so you won’t be
> caught?
>
> Emery Stora
>
>> On Dec 1, 2020, at 9:32 AM, James Hupy via Gmclist gmclist@list.gmcnet.org> wrote:
>>
>> Mark, that audio made my morning! Thanks for the trip down memory lane.
>> Great stuff.
>> Jim Hupy
>> Salem, Oregon
>>
>>> On Tue, Dec 1, 2020, 7:38 AM Mark Sawyer via Gmclist >> gmclist@list.gmcnet.org> wrote:
>>>
>>> 1967 Isle of Mann TT - Honda Hailwood Six:
>>>
>>>
>>>
> https://www.visordown.com/reviews/product/audio-hailwood-honda-six-full-song
>>>
>>> Sound of their own, indeed....
>>>
>>>
>>> --
>>> Mark S. '73 Painted Desert,
>>> Manny 1 Ton Front End,
>>> Howell Injection,
>>> Leigh Harrison 4bag and Rear Brakes,
>>> Fort Worth, TX
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>> _______________________________________________
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>
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| Re: [GMCnet] Final Drives [message #360433 is a reply to message #360430] |
Tue, 01 December 2020 11:05 |
stu@97381.com, Emery
Messages: 232
Registered: June 2020
Karma: 2
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Senior Member |
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I’ve never been sure what “I drive it like it’s stolen” means. Does that mean you drive carefully within the speed limit so you hopefully won’t be pulled over or does it mean you drive as fast as hell so you won’t be caught?
Emery Stora
> On Dec 1, 2020, at 9:32 AM, James Hupy via Gmclist wrote:
>
> Mark, that audio made my morning! Thanks for the trip down memory lane.
> Great stuff.
> Jim Hupy
> Salem, Oregon
>
>> On Tue, Dec 1, 2020, 7:38 AM Mark Sawyer via Gmclist > gmclist@list.gmcnet.org> wrote:
>>
>> 1967 Isle of Mann TT - Honda Hailwood Six:
>>
>>
>> https://www.visordown.com/reviews/product/audio-hailwood-honda-six-full-song
>>
>> Sound of their own, indeed....
>>
>>
>> --
>> Mark S. '73 Painted Desert,
>> Manny 1 Ton Front End,
>> Howell Injection,
>> Leigh Harrison 4bag and Rear Brakes,
>> Fort Worth, TX
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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