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Will going to a SM465 hurt my MPG?

Discussion in 'The Garage' started by bigredblzr, May 5, 2004.

  1. bigredblzr

    bigredblzr 1/2 ton status

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    I have a 91 K5 with a TBI 350, with 4.10s and it had a 700r4/np241. In the next week or so I'm gonna go to a SM465/NP205 set up. I was just wondering how it would effect may MPG. My guess is that it would remain about the same, but I'm not sure. Does anybody know?
    Thanks,
    Nate
     
  2. justinf

    justinf 1/2 ton status

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    You will lose some MPG, since the 700r4 was an overdrive tranny and the sm465 isn't
     
  3. bigredblzr

    bigredblzr 1/2 ton status

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    The 4th gear on a 465 is 1:1, what is the OD on a 700?
     
  4. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    [ QUOTE ]
    what is the OD on a 700?

    [/ QUOTE ]

    I believe it is 0.75:1 for fourth in a 700r4 . /forums/images/graemlins/k5.gif
     
  5. BlazerGuy

    BlazerGuy 3/4 ton status

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    Your gonna lose some...what size tires do you have?
     
  6. heavy4x4

    heavy4x4 1/2 ton status

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    [ QUOTE ]
    [ QUOTE ]
    what is the OD on a 700?

    [/ QUOTE ]

    I believe it is 0.75:1 for fourth in a 700r4 . /forums/images/graemlins/k5.gif

    [/ QUOTE ]

    .70
     
  7. 1-ton

    1-ton 1/2 ton status Premium Member

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    I actually consider an SM 465 transmission a 3-speed transmission. You will never use the Granny 1st gear on the street. The only time I ever used the Granny gear on my 465 was to pull other trucks out of the mud.
     
  8. atho

    atho 1/2 ton status

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    if you have a modded V8, lift, and bigger tires, the OD won't even offer that much of a fuel economy savings over the SM465. only thing it will do is keep the revs down on the highway.
     
  9. kennyw

    kennyw N9PHW Premium Member

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    [ QUOTE ]
    I actually consider an SM 465 transmission a 3-speed transmission. You will never use the Granny 1st gear on the street. The only time I ever used the Granny gear on my 465 was to pull other trucks out of the mud.

    [/ QUOTE ]

    I use granny low everyday... Just depends on what you are doing with your truck /forums/images/graemlins/thumb.gif
     
  10. blazen91

    blazen91 1/2 ton status

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    Don't mean to sound like a d**k, but we all drive big vehicles with big tires, low gears and V8's. Does milage really matter? /forums/images/graemlins/confused.gif
     
  11. m j

    m j 1/2 ton status

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    the driveability goes down a bunch with the ugly gear spacing
    once you are in direct with the 700r4 I think it locks up the convertor
    so there will be a steady cruise mileage loss with the lower geared sm465
    hard to say how much the convertor slip costs you in local daily driving fuel consumption
     
  12. James670X

    James670X 1/2 ton status

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    I've got the SM465 behind my 454 EFI and like others have already said 1st gear is granny low and is not very viable on the street (it's great to have when you need it though). The other point about bad gear spacing is also a very good point as well. Imho despite it's pitfalls the SM465 is a far better trans than the 700R4.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    One thing I hadn't really thought of before, but which was brought to my attention, is that fuel injected setups handle cruise much better without "bogging" like carbs do...you can "lug" the engine a lot more than you can a carb, and still maintain economy.

    If you are seriously concerned about MPG, you could keep your eyes open for a more cruise friendly axle set, probably around 3.42. The 465 will easily hide the gear difference probably up to a 33" or so tire (changing to 3.42 from 4.10 with 35's would be more noticeable) so that is a viable option, IF you are that concerned about it.

    This is all freeway though. Honestly, I don't think anyone has done anything at one time that netted more than a 2MPG decrease or increase in town. A swap of a big block, 1 ton running gear, and 36" tires would probably ruin in town mileage, but losing the OD tranny alone isn't going to affect mileage in the city noticeably, and more than likely will increase it if you drive sanely.

    I ended up with the same in town mileage with my 350/465 combo and my 305/700R4 combo. Dad swapped a BB from 350 into his 3/4 ton with 4.10's, and saw MAYBE a 1MPG decrease in city driving. Freeway was at least 2MPG less, but you can see that weight is a problem in town, and that is almost impossible to decrease enough to notice.
     
  14. bigredblzr

    bigredblzr 1/2 ton status

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    I have 35-36s. I know that I shouldn't be too concerned about gas mileage, but it is a dd, and if it dropped significantly, it would NOT be good. /forums/images/graemlins/tongue.gif
     
  15. blazen91

    blazen91 1/2 ton status

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    [ QUOTE ]
    I have 35-36s. I know that I shouldn't be too concerned about gas mileage, but it is a dd, and if it dropped significantly, it would NOT be good. /forums/images/graemlins/tongue.gif

    [/ QUOTE ]

    I can understand that. I just try to remind myself that gas milage ever becomes a concern for me, then it is time for a Honda. Good luck with your swap. /forums/images/graemlins/thumb.gif
     

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