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Changing gas mileage by lowering gear ratio

Discussion in 'The Garage' started by eshorvath, Sep 9, 2005.

  1. eshorvath

    eshorvath 1/2 ton status

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    I keep seeing these guys, with stock blazer tires, getting 17-24 mpg.
    Does adding 35" tires really reduce the MPG as much as 7-10 mpg, because im only getting 12mpg.

    If so, would lowering the differential gear ratios to making the engine closer to stock, like adding 4.11, return the gas mileage, or would it get worse? Highway, maybe worse, but the speeding up to speed, and local driving, way worse?

    Any input?
    I know the differentials would cost a lot, but besides that, would the mpg increase enough to notice...especially with the 3.25/gal

    Eddie
     
  2. Skigirl

    Skigirl 1/2 ton status

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    I have 4.10s and 35" tires and my MPG sucks. With a cleaned out, new fuel system my mileage has improved a little, to maybe 10-11 MPG highway from 9-10 MPG.
     
  3. no1uknow

    no1uknow 1/2 ton status

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    I have 4.10's with 35's and a 454 and get around 15 on the highway. I don't know what it does around town since I don't drive it in town.................
     
  4. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    i went from stock 265/75r16s and 3.42s with OD (14 mpg), to 35s and 3.42 without OD (9mpg) to 35s and 4.10s without OD (12mpg). i also swap from a fresh 350 that was stock to a healthy 355 and didn't see any difference in millage change before i put the 4.10s in.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Anything gas over 18MPG I'm gonna want to see for proof.

    Raising the truck does seem to increase fuel consumption, but even with my 33's I managed to pull down 18MPG, but that was *best economy*, not an average at 60MPH.

    If people didn't correct their speedometers, or use GPS to calculate economy after changing gears or tires, then the MPG numbers are worthless.
     
  6. dallassnowman

    dallassnowman 1/2 ton status

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    You need a 6.2 diesel!! :doah:
     
  7. ntsqd

    ntsqd 1/2 ton status

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    Based on the wandering I see in my GPS's "cookie crumb trail" I'm having less faith in it's odo being accurate than I used to. It's still more accurate than a mis-calibrated odo though.
    Patch the Wonder Yota, is nailing down just barely over 20 IF I keep it under 70 mph. This on 33-10.5's and ~3.5" lift.

    Speed is a BIG varible. Wind resistance is squared with speed, so a small increase (or decrease) in vehicle speed results in a large change in wind resistance.

    You need to drive with engine at or just slightly below it's Peak Torque rpm. That is where the engine will be the most efficient (power per gallon of fuel). For ideal mileage you then need to gear the truck so that it goes the speed you want to cruise at when it is turning that rpm.
     
  8. Zeitler

    Zeitler Registered Member

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    i've heard that a vacuum gauge can do wonders..but i have no idea how it all works
     
  9. eshorvath

    eshorvath 1/2 ton status

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    Drive and shift keeping the vacuum at the highest level.

    HArd to get used to, but once you do, it does work wonders.

    I used to have that on my 73 Datsun with the 91 350ci chevy.

    Just dont know where to get a new gauge to put into my truck, dont see them in the stores much anymore
    Eddie
     
  10. sledheadak

    sledheadak 1/2 ton status GMOTM Winner

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    with a 305/th350/2/73 gears with 36" tires i get 17-19 on the hyway and 10-14 on the trail in low range,but it is a gutless wonder.
     

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