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  1. #1
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    Default Xy 393 diff ratios? 3.25 or 3.5

    Hey guys

    wondering if anyone can help me.
    I have an xy with a 393 Cleveland, 9 inch 3.25s,
    c4 with 2500 stall (I think).

    It goes well but want a bit more poke.

    Should I go 3.5.1 gear ratio?? Or stick with 3.25?

    Itís a weekend cruiser. Do a bit of freeway driving here and there.

    Id really appreciate some advice or anyoneís thoughts?

    thanks in advance 👍

  2. #2
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    Default

    hi
    What u forgot to mention is tyre size and diameter. ????????????
    Different tyre diameters have a huge influence on what rpm u have at 100kph
    Most likely 3000rpm at 100kph is about the limit for comfy cruzin ,not noisey but not quiet . Depends on engine mods as well rpm at 100kph

    Do u no what cam ,heads, compression, intake ????. This influences rear gear

    C4
    2500stall
    rear gear ratio ???

    Look up US Gear u will be surprised as what is available
    They have a many ratios available even inbetween ratios Available types Drag/street/isotropic/stealth
    eg 3.25 3.4 3.5 3.6 3.7 3.8 etc etc
    Ring & Pinion | Ford | 9" | Products | US Gear


    I just fitted 3.6 gr to a 660-670mm diam tyre

    The later HSV commodores can have 3.7 with a 670--690 tyre . Remember these have a double overdrive transmission to cut the revs down at highway speeds .
    Last edited by swampy; 04-12-2018 at 10:26 PM.

  3. #3
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    Default

    Cheers. Much appreciated.. Iíll have to pull out the spec sheet on the motor i think. Just so Iím understanding this correctly, at the moment itís sitting on 235/55/14 and it sits on or around 2500rpm at 100ks. If I did nothing but change tyres to 255/60/15 would this increase or decrease rpm at 100ks

  4. #4
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    HI
    235/55/14 never seen one . This makes more sense 235/60/14 tyres

    2500rpm for 255 60 15 3.25 rear gear
    2700 rpm 235 60 14 3.25 r gr

    2700 255 3.5
    2920 235 3.5 very common choice for this tyre size

    2770 255 3.6
    3000 235 3.6

    2855 255 3.7
    3080 235 3.7


    Gearing is influenced on how modified the engine is . Modded engines like to rev a little .
    Last edited by swampy; 05-12-2018 at 09:20 AM.

  5. #5
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    Default

    Cheers. Thanks for the info. Makes more sense now. Appreciate it 👍

  6. #6
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    Default

    This is a very broad ask for something to go better without knowing any motor specs etc.
    Does that little 2500 converter match the motor ? Is it actually a 2500 converter? Was the converter built specifically for this motor? What heads ? What intake? What cam ? What carb? What ignition? How is the timing set up ?
    Is the gearbox good ? Could it be slipping? Does the motor make more torque than the converter can take & Blowing through the converter?
    The diff gears are only one small part

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