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Thread: 2.73 rear end gear ratio good or bad

  1. #1
    Senior Member Chevy_Finatic79's Avatar
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    2.73 rear end gear ratio good or bad

    I know everyone wants 3.73 or 4.10 gear ratios for hi perfomance cars/trucks but how does a 2.73 compare the only thing I can think of is that is spins lower hiway rpms and is fuel friendly. I could be wrong rear ends arent my thing

    what is the most Ideal gear ratio for a full size 85 1/2 ton chevy truck?

    I dont want a 4.10 becuase I will be on the hiway quite a bit and hi rpms drive me nuts I hate whining. I'd like to get in the 3.'s at the very least though 3.40's or better.

    I know there is a math equation to find gear ratio and thats all great on paper I want real life hands on feedback tho. so any one out there that has swaped out a bunch of rear ends to find that Ideal gear ratio I need your opinions and feedback.

    5.7/THM350

    Thanks Slicc
    "She's gonna Freak when she see's my wheels"

    85' Chevy C-10 Longbox (Rat)
    TBI 327 Cu.In./THM350

    90' Chevy Suburban 4x4
    TBI 350 Cu.In./700R4

    http://www.truckforum.org/forums/truck-pictures-176.htm

  2. #2
    Senior Member
    75K30's Avatar
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    The ratio charts can be your friend. They will provide you with the proper ratio to keep you engine at the proper rpm.

    While we have had several discussions with regards to gear ratios, and I will bring back up a few key points.
    Far too many folks are concerned about highway rpm's and they believe that the lower the rpm's the better. While this is fairly true for most cases, many fail to realize that vehicles have to still produce a given amount of torque to maintain foward motion. If the ratio is too high (numerically lower) like under the 3.0 range, and the taller tires of a truck is not compensated for, the truck will be foreced to work harder to maintain the same speed, and would be counter productive. Chances are, it will take more throttle to just slightly accelerate, and if too much throttle is required, the transmission will downshift, taking the engine rpms way higher than it would if the truck was equiped with a better gear.
    As long as we are talking about acceleration, we should also discuss how often this vehicle has to start from a dead stop. This ratio wil make it diffficult to maintain speed, it will also make it more difficult to roll from a stop. All of this will take a toll on mileage averages. This is where a ratio that provides a mechanical advantage is far superior.
    The weight, and the tire diameter of a full size truck makes me really have to suggest the right ratio for a given application, and a ratio that is suited for a lighter car, with shorter tires may not be the best for this truck.
    Tire size is an important factor that has been left out here.

  3. #3
    Senior Member
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    I've always been told that for the best fuel mileage keep the engine rpm where it makes the most vacuum. But, nobody ever clarifys manifold or port vacuum. it makes some sense, but still somewhat unclear.
    Joe
    89 K2500 Chevy, Wee-Oh-five 294K miles
    1962 Scout 80 parts I guess
    1966 Scout 800 resto job
    2005 Chevy 2500HD Short cab long box DURAMAX
    1996 P30, 6.5 NA Mac Mobile
    whole lot of buicks

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