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Thread: Optimizing gearing, Hemi / 545RFE / Atlas 4.3.1 and Tons

  1. #1
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    Optimizing gearing, Hemi / 545RFE / Atlas 4.3.1 and Tons

    I am starting to look at my build parts and am in the process of trying to determine the best ratios for gearing...


    The only components i currently have are the

    2007 5.7 HEMI motor
    2007 545RFE 5 speed auto tranny, which has gearing of:
    • 1st 3.00:1
    • 2nd 1.67:1
    • 2nd Prime 1.50:1
    • 3rd 1.00:1
    • 4th 0.75:1
    • 5th 0.67:1
    • Reverse 3.00:1




    I want to go with an ATLAS, probably the 4.3.1 and then tons for axles...

    What i am now trying to do is determine what would be the optimum gear setup in the diffs to maximize offroad/trail/crawl use but at the same time road use.

    Gearing + Countryboy = does not compute!!!!!

    Any online guides or for that matter, anyone have any clear suggestions?

    Cheers,

    EDIT: should have mentioned that i intend on running 39-42" tires.
    Last edited by countryboy; 08-05-2012 at 02:15 PM.
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    Yeah, been there done that. The problem with this is that it does not take into account HP. I'd love to hear more from those with real world examples... I.E. With these kinds' of tranny gears and a 4.3.1 atlas, 42's, what's the best axle gears i should be looking for.... Kind of thing.

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    The way I decieded to look at gearing is since I have a granny low gear for off road why not pic a good highway gear for the jeep and sticking to 35's. The chevy 5.7tbi will be plenty of power and with the 410's cruises at a nice low 1700ish rpm at highway speeds.

    Don't know if that helps.
    My latest project... Collection of Parts

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  5. #5
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    I have
    - 3:54's with 35's in the YJ running a mildly worked over 5.2L, 42 RH, 231.
    This set up worked well on 33's but is slugish on 35's. If I keep this Jeep, I need to regear to 4:10's

    - 5:38's with 42's in my CJ. LT1 350 TPI engine in front of a worked over T350 & D300.

    You probably already know this stuff....
    Ring gears get physically smaller as you increase the gear ratio. Meaning 4:10 R&P is stronger than 5:38 R&P. Let's face it, 4:10's are not the gear to run with 42's and expect to have optimum performance.
    RPM's build HP. No RPM's no power

    according to the numbers
    -6:17 would be just over 1500 rpm's in 5th gear at 65mph. a little slugish
    - 7:17 your RPM's would be 1800 in 5th gear at 65mph. a better choice.
    A stock jeep as a base line runs at around 2300 rpm's @ 65mph.
    Problem with these gears, if you can get them, they're weaker if you plan to beat on them and only available in regular cut. This limits your axles.

    Just my experiances so far. Do you really think you'll ever drive a large distance on the highway. The cost of the tires, the heat score from Johnny Law, and my favorite...the insurance industry classifies your built rig as "modified for racing" and flips you off. Good Luck I hope this sheds a little more light on your dilema.

    ---------- Post added at 01:40 PM ---------- Previous post was at 01:35 PM ----------

    In case you didn't have this info already.
    http://www.pirate4x4.com/tech/billavista/60_front/
    Last edited by toofargone; 08-06-2012 at 10:50 AM.

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