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Thread: How to determine rear axle ratio in a back half car??

  1. #1
    Senior Member SENIOR BUILDER
    Join Date
    May 2004
    Location
    Loganton, Pa
    Posts
    113

    How to determine rear axle ratio in a back half car??

    I am biting the bullet and selling my brand new rear end that I had built for my 70 Buick Skylark. I am now in the midst of getting a S&W A body ladder bar back half kit and will be installing my 15x14 Buick ralley wheels on the car. It is suggested a 31x18.5x15 slick can be used but I have 14 inch wide rims and the tire suggested is 14.5. Should I get the 14.5's? I am also going to a Ford 9 inch rear with rear disc setup (stock pieces) I am running a TH 400 trans with reverse pattern manual valve body. My motor will be built to operate in the 6000 rpm range and I need to determine rear gear ratio. Any suggestions to what I should shoot for??
    Pat Harmon
    1970 Skylark 455 ALL-PARTS Racecar
    1973 Buick GS 350 4 spd 1 0f 365
    1986 Buick Century GS number 2
    1986 Buick Century GS number 3
    1986 Buick Century GS number 4

  2. #2
    Member JUNIOR BUILDER
    Join Date
    Sep 2008
    Location
    DELAWARE
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    94
    HEY BIG,On the site,www.hardcore50.com,they have some math formulas for working out rear end ratios and such.Maybe it might help you.FISHMANJOE

  3. #3
    Senior Member RACING JUNKIE
    Join Date
    Jan 2006
    Location
    La.
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    2,890

  4. #4
    Senior Member SENIOR BUILDER
    Join Date
    May 2004
    Location
    Loganton, Pa
    Posts
    113
    Thanks for the links guys..It was really helpful. By doing some initial calculations as well as asking a friend who has a similar build to what I want,Looks like in the 4.30 range is where I need to be.
    Pat Harmon
    1970 Skylark 455 ALL-PARTS Racecar
    1973 Buick GS 350 4 spd 1 0f 365
    1986 Buick Century GS number 2
    1986 Buick Century GS number 3
    1986 Buick Century GS number 4

  5. #5
    Senior Member RACING JUNKIE
    Join Date
    Feb 2004
    Location
    san antonio, texas
    Posts
    1,233
    4:56 works well with that size of tire, good luck :wink:

  6. #6
    Member MASTER JOURNEYMAN
    Join Date
    Nov 2007
    Location
    annapolis md
    Posts
    43
    4.56;is what i ended with w/32in.tall tire 4.10 was at 5500 at traps
    56 was 6100 good luck!


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