1. haybag

    haybag Well-Known Member

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    Found an abody 8.25 rear I am interested in buying to upgrade the 7.25 in my 71 Duster. Seller says it's a sure grip and has a 2.71 tag on it. If I buy it I would eventually want to put 3.55 gears in it. I have seen that there are 2 different rears , but only one will accept the higher numerical gears. thought I had read it was 2.76 . Can anyone confirm or deny if this rear with 2.71 can be upgraded to 3.55"s ? Thanks
     
  2. Slantsix64

    Slantsix64 Well-Known Member

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    Yup can upgrade to any ratio
     
  3. robert flippo

    robert flippo Well-Known Member

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    just finished changing a 271 to a 355 on my 74 duster, had a little problem getting old pinion out , but other than that, no problem.
     
  4. haybag

    haybag Well-Known Member

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    Thanks for the responses, just wanted to make sure I wasn't setting myself up for problems.
     
  5. halifaxhops

    halifaxhops It's going to get stupid around here! FABO Gold Member

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    Your good its the 2.45 rears you cannot do it to.
    lots of info here.
    The 8 1/4 thread
     
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    • lemondana

      lemondana BlackDart

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      Drive it with the 2.71's for awhile if you do any freeway or interstate driving. you can run 80 all day long. Unless you have an overdrive, then disregard. I give up performance to be able to run out on the road. I do a lot of interstate driving.
       
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      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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        From 2.71s to 3.55s is a heckuvan increase ~31%. . This 31% is about the same per cent as downshifting from second gear in an A833 to first gear. The torque increase is throughout the operating range, making the engine feel that much more powerful at all rpms.
        The downside , as mentioned, is that the hiway cruise rpm will be similarly increased, as will the fuel-consumption.
        If you need more power, and need to keep the cruise rpm, or fuel economy;
        then you only have about three/four choices, in order of cost;
        1) a bigger engine,
        2) hot-rodding your engine,
        3) supercharging,
        4) an overdrive trans in conjunction with a rear gear-swap, or an overdrive with a deep low.

        Swapping in a bigger already good-running used engine is usually the cheapest option. And starting with a high-compression one is by far the smarter choice.
        Supercharging is guaranteed to make you smile, and the belt-driven ones are quick and easy
        HotRodding is the usual go-to; but sometimes takes a lotta time and the results are somewhat unpredictable when parts are just thrown together, or the bottom falls out of the budget.
        The overdrive plus gears, is probably gonna be the most expensive, but can have the added benefit of decreasing your hiway fuel consumption. But don't do it for gas savings it will take many years and many miles to break even.

        Gears are quick and relatively easy, and you'll never be sorry from a performance viewpoint.
         
      • haybag

        haybag Well-Known Member

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        I am putting this duster together as a street car that I can take to the drag strip a couple times a year, will be a mild 5.9 magnum. Don't do much freeway driving, mostly around town driving, so some mid range gears should give me some performance along with drivability.
         
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