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MPG with 3.73 axle gears

Discussion in '1982-Present GM Diesel' started by 84CUCV, Nov 26, 2004.

  1. 84CUCV

    84CUCV 3/4 ton status Premium Member

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    The truck has 6.2 400/208 combo. I might be taking out, 4.56 gears and put in rears with 3.73. What kind of MPG will i get? Will i be able to do 70 on the parkway? No sure how to fugure this out on my own. thanks for the help!

    Mike
     
  2. bigblock454

    bigblock454 Clack Clack Clack Premium Member

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    My K2500 6.2 Burb with a th400, 3.73s and 31s could get 19 MPG if kept around 65. It would do 75 or 80 maybe but sure screamed down the road.
     
  3. 84CUCV

    84CUCV 3/4 ton status Premium Member

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    OK thanks mike
     
  4. Pookster

    Pookster 1/2 ton status

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    it will do it, but I dont think you'll see the fuel economy that your looking for. Take it down a few notches to 55, then you'll see 20+ . /forums/images/graemlins/smile.gif

    Leave the 456 in, put in 33 or 35" tires. /forums/images/graemlins/smile.gif
     
  5. 84CUCV

    84CUCV 3/4 ton status Premium Member

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    that one thing i never thought of. thanks
     
  6. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    With 4.56's, 31's and a non OD tranny you would be turning 3,213 RPM's at 65mph.

    With 3.73's and the same combo you would be turning 2,628 RPM's at 65mph.

    With your current 4.56's and you step up to a 35" tire... 2,845RPM's at 65mph.

    For the best fuel mileage you want to be around 2,000RPM's. I get 20+ at 70mph turning 1,800 RPM's with 3.54 gears and true 31's on my Dodge cummins.

    I would consider a taller tire for the cheapest route but if you really want to get the best mileage you should consider swapping to a Th700R4 or NV4500. The first gen dodge cummins 89-92 had the option of a 5 spd manual and a torquer flight 929. You got 4.10's behind the 5 spd and 3.07's behind the 3spd auto. THe clear choice is the manual but the problem was that it wasn't an NV4500 yet but a underrated LD tranny that had many problems. The TF auto worked fairly well but the high gears hurt acceleration and towing performance.

    My point is is you could gear way up but with slower acceleration as a consequince. IMHO, an OD tranny is the way to go.
     
  7. jac6695

    jac6695 1/2 ton status

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    [ QUOTE ]
    torquer flight 929

    [/ QUOTE ]

    /forums/images/graemlins/thinking.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/histerical.gif
     
  8. 84CUCV

    84CUCV 3/4 ton status Premium Member

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    OK know a good shop for 700r4s? thanks
     
  9. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    OK know a good shop for 700r4s? thanks

    [/ QUOTE ] Yes, the custom shop that built mine.....but you are in NJ and I'm in Cali. /forums/images/graemlins/smile.gif Bowtie OD builds a nice 700...
     
  10. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    [ QUOTE ]
    torquer flight 929

    [/ QUOTE ]

    /forums/images/graemlins/thinking.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/histerical.gif

    [/ QUOTE ] /forums/images/graemlins/confused.gif /forums/images/graemlins/dunno.gif
     
  11. jac6695

    jac6695 1/2 ton status

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    I do it too: should be Torqueflite 727 /forums/images/graemlins/deal.gif
     
  12. 84CUCV

    84CUCV 3/4 ton status Premium Member

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    Thanks i will check it out. mike
     
  13. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    I do it too: should be Torqueflite 727 /forums/images/graemlins/deal.gif

    [/ QUOTE ]IIRC there was the TF727 and heavy 929 model.
     
  14. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    [ QUOTE ]
    I do it too: should be Torqueflite 727 /forums/images/graemlins/deal.gif

    [/ QUOTE ]IIRC there was the TF727 and heavy 929 model.

    [/ QUOTE ]

    The Torqueflite 727 was the heavy duty.
    The 999 is the other one you are looking for.
    They also have a 904 light duty.
    I can't remember if the 999 was an OD or the 904 but the 727 was not.
     

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