Rear ends 4.10, for 3.55 or 3.73
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Join Date: May 2006
Location: North Plains, Oregon
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RE: Rear ends 4.10, for 3.55 or 3.73
Ahhhhhh, I'm gonna throwthe saying about gear ratio swaps for fuel mileage out there again......
Changing gears for fuel economy is like getting a Diet Coke with a Double Whopper Meal..........it just doesn't have the desired effect.
Basically, you are looking at around a $600 - 1000 for a 2X and double that for a 4X.
You can buy a LOT of fuel for that, let alone make up the difference in what you'd realistically see.
The only time that changing gears is necesary and economical is to restore performance with lift / tire size changes or to increase towing. Otherwise, you'll be throwing money down the drain.
Changing gears for fuel economy is like getting a Diet Coke with a Double Whopper Meal..........it just doesn't have the desired effect.
Basically, you are looking at around a $600 - 1000 for a 2X and double that for a 4X.
You can buy a LOT of fuel for that, let alone make up the difference in what you'd realistically see.
The only time that changing gears is necesary and economical is to restore performance with lift / tire size changes or to increase towing. Otherwise, you'll be throwing money down the drain.
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RE: Rear ends 4.10, for 3.55 or 3.73
Both Dodge and GM believe
that the number of mph/1000 rpm
is important to Diesel economy.
That is why ex-GM foundary American Axle
(which was taken private by ex-Chrysler managers laid off by Daimler after the Daimler/Chrysler merger)
is developing new differential gears for the 10 and 12 bolt diffs.
Ex-Chrysler VP, and now GM head of design,
Bob Lutz ordered American Axle to come up with the 3.42 ratio that is now used in the base GM pickups this year.
Any diesel owner can see for themselves what rpm effect there is on mileage by simply doing test runs in 3rd gear, then do the same stretch of road in 4th gear.
Those diesel owners with GearVendors Underdrives installed can even further experiment this way:
http://dieseltruckworld.tenmagazines...e&aid=2798
sample quote:
"Would you believe me if I told you that a full-size, diesel powered pickup can get 30 miles per gallon while being driven at 75 miles per hour? Like you, I might believe it, but I would still want to see some proof with my own eyes."
There is a interesting Society of Automotive Engineers Journal paper from about 25 years ago where they installed two Laycock underdrive units in a row on a gasoline vehicle's drivetrain behind a manual 4 speed trans
(this gave them 16 speeds)
then did testing at various speeds and engine rpms.
MPG improved up to ratios of 40 mph for every 1000 rpm.
Now the new Tundra 6 sp auto has a top overdrive ratio of 0.59 with 4.10 rear differential ratio. (I will let you figure out the mph/k-rpm with 29 inch tires, it is worth the effort)
Cummins also has given their official word on how engine rpm affects fuel economy, and they say keep the rpm low:
http://www.cummins.com/na/pdf/en/pro..._Whitepape.pdf
that the number of mph/1000 rpm
is important to Diesel economy.
That is why ex-GM foundary American Axle
(which was taken private by ex-Chrysler managers laid off by Daimler after the Daimler/Chrysler merger)
is developing new differential gears for the 10 and 12 bolt diffs.
Ex-Chrysler VP, and now GM head of design,
Bob Lutz ordered American Axle to come up with the 3.42 ratio that is now used in the base GM pickups this year.
Any diesel owner can see for themselves what rpm effect there is on mileage by simply doing test runs in 3rd gear, then do the same stretch of road in 4th gear.
Those diesel owners with GearVendors Underdrives installed can even further experiment this way:
http://dieseltruckworld.tenmagazines...e&aid=2798
sample quote:
"Would you believe me if I told you that a full-size, diesel powered pickup can get 30 miles per gallon while being driven at 75 miles per hour? Like you, I might believe it, but I would still want to see some proof with my own eyes."
There is a interesting Society of Automotive Engineers Journal paper from about 25 years ago where they installed two Laycock underdrive units in a row on a gasoline vehicle's drivetrain behind a manual 4 speed trans
(this gave them 16 speeds)
then did testing at various speeds and engine rpms.
MPG improved up to ratios of 40 mph for every 1000 rpm.
Now the new Tundra 6 sp auto has a top overdrive ratio of 0.59 with 4.10 rear differential ratio. (I will let you figure out the mph/k-rpm with 29 inch tires, it is worth the effort)
Cummins also has given their official word on how engine rpm affects fuel economy, and they say keep the rpm low:
http://www.cummins.com/na/pdf/en/pro..._Whitepape.pdf