Of course you do. That's why you refer to torque as a parameter in top speed results.

the term "higher" is due to those used to dealing with transmission shifts...
4th gear is "higher" than 2nd gear...

the diff and or transmission gear RATIO's should use the term "taller" or "shorter"

the "higher" gear ratio is a "shorter" GEAR
the "taller" gear ratio is a "lower" GEAR numerically... this is why it's not good to discuss higher or lower when talking about gear ratio's... cause it's confusing...

so, in short...
higher and lower are terms you should only use when counting shifts in a transmission, and taller and shorter are terms you should use with gears...
and the word ratio should be left out of the conversation altogether...
whiew!


of course, you could use bigger and smaller... but that will bring up an totally different confusion and bragging and such...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

HMMM.................Ok.


Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Hi-
I really appreciate all your thoughts on my analysis. I was about to attach the excel file that I cleaned up a bit, but I just realized that I cannot attach a .xls file. Wish I had noticed that before I spent the last few hours tidying it up. Oh well. Anyway, I think Army was the only person who asked for it, so I will send it to him directly.

Andrew

And I'm looking forward to it. I reckon there's still some mileage in doing these types of calculations!

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

To the OP......I would not hesitate to change the diff but not to increase fuel economy. I would expect little gain there. It would make the motor quieter on the highway.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Yes, but you thought that 288 divided by 307 was a 9.6% od effect.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Calculation error...........since corrected.

The fuel benefit was 1 mpg.........about 1/2 of your predicted 1.7 mpg based upon the ratio.

This benefit holds true for most vehicles that undergo the diff change...........except yours. You manage to violate all laws of physics by getting the exact fuel economy percentage as the ratio change. Magically, the force required to dispel the air has also been reduced by the same differential percentage on your vehicles. Additionally, the work required to accelerate the vehicle around town is also reduced by the same differential percentage on your vehicles.

Consistency in thought is a wonderful attribute.

Unless I had a bad diff, I would never have changed from a 307 to 288. Not enough benefit there.

I'd be happy to share the log books from before and after diff swaps in my cars with you. And the before and after results from the five speed od swap into the 83 240/300D. I don't claim all the answers but I have documented results and over multiple vehicles.

The correlation is not exactly 20% but close enough for rules of thumb, in my experience.

It is not possible to control every variable so rules of thumb are close enough for me.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

'Higher' and 'lower' are used all the time in regard to transmission gears so the meaning can easily be transferred to different differential ratios.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

In order to benefit from a taller gear ratio you have to have some available power to exploit. There is not much to work with with the 220D.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

with gear ratios in diffs, think of it like climbing stairs.

a 6' incline is harder to climb with 2 steps than with 4 steps... so a 2:1 ratio is TALLER than a 4:1 ratio...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Good one!

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

thanks, it just came to me driving down the road thinking on this thread...
I'm sure it's been stated elsewhere before though...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!