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#1
09-15-2011, 05:00 PM
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2.88 differential fuel mileage questions
What is to be expected in terms of improved fuel mileage if I were to switch from a 3.07 to 2.88?? Say cruising about 65-70mph?? How about in-city fuel mileage??
- Thank You.
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'81 300SD- OM617.951, Euro Head Lights, Hella 550's, 2.5" Turbo-Back Straight Pipe, ALDA Removed, Camo Dash + Seat Covers, Boost Gauge, DU Floor Mats, Cobra CB, LED Trunk lights, and other things...  '03 Chevy CCSB LT LB7 "P-Stroke Killer" 219K mi. - AirDog II 165, EFI Live, Alligator Stage V, ISSPRO EV2 Pyro/Boost, PPE Boost Valve, LML Manifold, MBRP Downpipe, Debadged, Bills Custom 3.5" Turbo Horn, B&W Hitch, S&B Intake Last edited by Duckinator; 09-15-2011 at 05:26 PM. 
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#2
09-15-2011, 05:34 PM
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Probably barely anything.
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-diesel is not just a fuel, its a way of life-  '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k)
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#4
09-15-2011, 06:48 PM
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Several years ago, I swapped the slightly noisy 3.07 in my '84 300D for a good 2.88.
No real difference in economy (maybe a 1/2 mpg at best...I never could get solid economy info out of that car) but it did drop the revs at 65mph to 2750ish.
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Never a dull moment at Berry Hill Farm.
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#5
09-15-2011, 11:25 PM
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I have a 2:88 in the 85 with a 4-spd manual, and you will pick up 3 mpg.
I have never driven the 3:07 to compaire, but there is about a 6.7% difference. 85`s all had the 2:88 Diff. 300D and 300SD. If you do swap in the Diff, grab the Spedo also. they are geared together. 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
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#7
09-16-2011, 06:14 AM
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I have monkeyed around changing diffs on quite a few vehicles. I expect on a diesel to improve equal to the mechanical difference. As charlie says it is slightly less than 7%. 7% would give about 2 mph more economy.
Changing from an auto to stick gave us a bit more than that in my 300 cd. It went from about 25 highway to nearly 30.
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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.
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#8
09-16-2011, 07:01 AM
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IIRC my '84 300D has the standard 3.47 diffy, and I'm considering the same swap to a 2.88. Is that worth the effort?
From the threads I've read on the subject it looks like my rpm at 65-70 mph would drop from 3,000 to about 2,500. Same threads don't really discuss mpg... just that the rpm drop puts the 0M617 squarely into it's power band. What kind of mpg increase might I see with the 2.88?
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1991 300D 2.5 "Rocinante" 2002 Golf TDI "Teen Spirit" -------------------- 1984 300D 1966 Mustang I6 3sp 1985 Mazda RX-7 GSLSE 1982 Toyota Supra 1977 Datsun 280z 1971 Datsun 240z
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#9
09-16-2011, 07:29 AM
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Quote:
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#10
09-16-2011, 07:53 AM
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Did all 123's move to the 2.88 gears in 85? My 85 TD seems to rev awfully high and I am wondering if the 2.88 only went in the sedans.
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1985 300 TD 448K 1984 300 TD 278K 1983 240D euro 240k 1994 f-250 idi turbo 330K 1986 f-350 IDI 1987 F-350 IDI 1985 JD 1050 4wd 1965 IH 3660
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#11
09-16-2011, 08:11 AM
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Quote:
The 3.07 is right at or just above 3000.......depending on tires. The 2.88 is at 2800 or just above. "Awfully high" is relative.
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#12
09-16-2011, 08:42 AM
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Quote:
__________________
1985 300 TD 448K 1984 300 TD 278K 1983 240D euro 240k 1994 f-250 idi turbo 330K 1986 f-350 IDI 1987 F-350 IDI 1985 JD 1050 4wd 1965 IH 3660
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#13
09-16-2011, 09:15 AM
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Quote:
Quote:
__________________
Never a dull moment at Berry Hill Farm.
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#14
09-16-2011, 09:31 AM
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I have both in 123 chassis (3.07 in the 82, 2.88 in the 85).
as others have said, 2.88 cruises at about 65 mph @ 2800 rpm, 3.07 is about 3200 for 65 mph. its a difference mostly in noise. maybe 2-3 mpg difference, but its barely noticeable. as having both, i personally wouldn't seek to swap to a 2.88 from a 3.07 unless there was something wrong with the diff and it had to be swapped anyways.
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------------------------------- '85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit) '82 300D, 'Tex', 228k body / 170k engine ... summer car '83 300TD Cali Wagon 210k, wife's car
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#15
09-16-2011, 09:31 AM
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Quote:
SIRNIK84 put one in his 84 300SD when he did the 4-spd swap, said it really improved his performance, is really happy with it. Charlie
__________________
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
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