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454 installed, Now what Diff gears should be installed?

Discussion in 'The Garage' started by BlitzK5, Sep 28, 2005.

  1. BlitzK5

    BlitzK5 1/2 ton status

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    I just installed a 3/4 ton running gear in my blazer (14 bolt FF rear & 10 bolt front) and a 454 , with a TH350 and a NP208 and new set of 38X15.5x16.5 Radial TSL's, which actually measure 37". I was wondering what gears to go with, 4:10, 4:56 or 4:88? The 14 bolt bolt has 3:73 already, should i just keep them or upgrade? My concern is at highway speeds like 60mph & 65mph my rpm will be way to high with no overdrive. Im trying to stay in the powerband at all speeds, which is 2200-2600 rpm I believe for a big block such as mine. I am going to be doing a lot of highway driving to get to places to go 4X4 so im concerned about the gas millage. Also since its a 454 should I even be worried about lower gears since I will ge the extra torque from the big 454. Should I keep it low in the power band to save on fuel?
     
  2. steve_kibbe

    steve_kibbe 1/2 ton status

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    454 = bad gas milage :o

    If you are that concerned, you could run your 3.73's and just wheel in low range. Since you have a 208, there's some advantage.
     
  3. BigCountryx

    BigCountryx 1/2 ton status

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    Lots of torque with too high of gear ratio is gonna put lots of strain on the tranny. Just something to keep in mind. 4.56's minimum IMO to take a little pressure off of the auto tranny.
     
  4. steve_kibbe

    steve_kibbe 1/2 ton status

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    Agree :D

    I'd put a tranny cooler on it aswell. Not just the in radiator type.
     
  5. tuffdogstudio

    tuffdogstudio 1/2 ton status

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    I have 3.73 gears with 33's and think 4.10s would be better for my rig... so I am guessing that the 4.56s would be a good choice for you.

    As for gas mileage, I get 10-12 outta my 454 in a 3/4 ton Sub. I dont know many folks doing any better except for diesel and I know I can beat the snot outta most diesel 'burbs.
     
  6. thebigdaddyof2

    thebigdaddyof2 1/2 ton status

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    Tuffdog,
    What trans are you running with the BBC and 3.73??
     
  7. 85mudblazin

    85mudblazin 1/2 ton status

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  8. shane74

    shane74 1/2 ton status

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    4.88's minimum IMO. I will be running the exact same combo. My setup will be 454/TH350/203-205 doubler, 4.88's, 38's or 40's. If I were running a 700-r4, I'd go with 5.13's or even 5.38's (if they ever become a reality).
     
  9. tuffdogstudio

    tuffdogstudio 1/2 ton status

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    700R4
     
  10. bigbadchev84

    bigbadchev84 1/2 ton status

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    i got 39.5s 400/465/208 with 4.56s its got balls and im running at about 1700rpm passing cars on the highway at a 55mph speed limit.....i dont have a speedo so i have no idea how fast i am actually going, but i wish i had at least 4.88s the 4.56s were great for a while i went from 3.08s to 4.56s what a difference, but after time it wears off and i wish i had just a little more grunt. if your worried about gas mileage then i think you are going the wrong route with big tires and a 454! I just bend over and take it at the pump......its the trade off for driving a truck with 14"lift with 39.5s
     
  11. TX_GLADIATOR

    TX_GLADIATOR Registered Member

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    what r your plans for the truck, if tou plant to go crazy later 513 if you ask my get it over w/ if you think you will end up a tire bigger then a 40 very soon

    if you going to use if for dd then i wouldn't no, i don't know how to mix those ratios :doah:
     
  12. BlitzK5

    BlitzK5 1/2 ton status

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    Would'nt the 454 make up for not having real low gears because of the added torque of the engine compared to a 350 or so. Also with only a TH350 (No overdrive) at higway speeds the engine rpm will be way out of the powerband.
     
  13. BigCountryx

    BigCountryx 1/2 ton status

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    Yes, I would think that the 454 would feel fine with the high gear ratio, but he has a "small block" tranny behind a big block motor in my opinion. I would want to lesson the strain on the tranny by running lower gears. Take a ten speed bike and put it in tenth gear, then try to take off. The amount of extra force you are pushing onto that pedal is the same as the extra force you're engine has to put on your tranny when you increase your tire size.
     
  14. BlitzK5

    BlitzK5 1/2 ton status

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    Ok thanks alot. I think I will go with 4:56, because 4:88 might be to small for the 10bolt
     
  15. gman454

    gman454 Registered Member

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    I run a well built 454 bored 60 over with a 350 hydro tranny and a np205 tcase with 4.56 gears and 39.5/15.5/15 and at about 65 I run between 2600 and 2700
    rpm. 4.56 gears are the way to go
     
  16. BlitzK5

    BlitzK5 1/2 ton status

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    4.56's it is then
     

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