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Engine revolutions questions

Discussion in 'Intermediate CJ-5/6/7/8' started by BobFortier, Jan 27, 2006.

  1. Jan 27, 2006
    BobFortier

    BobFortier Member

    Joined:
    Nov 24, 2005
    Messages:
    254
    Hello folks

    maybe it will seem a strange question, but I wanted to check this with you guys.

    I made a small calculation to check at what RMP I'm going to acheive a given speed using tire sizes in the equation, along with all the ratio of my drivetrain.

    With this, it says that with the tranny in 3rd, with the t-case in 2-high, with tires 29 inch dia. (approx) I'll have to rev the engine at 2500 rpm to acheive 60 mph.

    Since it is my first jeep, I just wanted to know if it is normal rpm or if it is too high



    Bob in Sherbrooke, Province of Québec
     
    BobFortier, Jan 27, 2006
    #1
  2. Jan 27, 2006
    sparky

    sparky Sandgroper Staff Member Founder

    Perth, WA
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    Sounds normal to me.

    What's your differential ratio?
     
    sparky, Jan 27, 2006
    #2
  3. Jan 27, 2006
    mb82

    mb82 I feel great!

    Charlottesville Va
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    2,706
    Nope thats not high at all. Consider modern 4cyl cars turn 3K at around 70MPH.
    What Motor BTW?
     
    mb82, Jan 27, 2006
    #3
  4. Jan 27, 2006
    BobFortier

    BobFortier Member

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    Nov 24, 2005
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    I have an inline 6, 258, and my diff ratio is (i did not check on the casing) but I found somewhere that my front diff in 1977 was geared at 3,54.


    Thanks folks

    Bob in Sherbrooke
     
    BobFortier, Jan 27, 2006
    #4
  5. Jan 27, 2006
    sparky

    sparky Sandgroper Staff Member Founder

    Perth, WA
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    Sep 20, 2002
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    Sounds right to me.

    3.73s in my '71 put me at 3500 RPM at 70MPH and 33's.
     
    sparky, Jan 27, 2006
    #5
  6. Jan 27, 2006
    w3srl

    w3srl All-around swell dude Staff Member

    Port Orange, FL
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    I got 2527 with 3.54 and 29" tires, so I'd say you are right on the money. I don't think I'd want it much lower than that, or your highway power is really going to suffer IMHO.
     
    w3srl, Jan 27, 2006
    #6
  7. Jan 27, 2006
    hudsonhawk

    hudsonhawk Well-Known Member

    North Texas...
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    4:56 and 35's I run at 2800 at 60.
     
    hudsonhawk, Jan 27, 2006
    #7
  8. Jan 27, 2006
    73cj5

    73cj5 Member

    Maine
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    Jan 15, 2004
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    905
    I'm at 2500rpm at 60mph also, I have 31's and 3.73 gears. As long as your engine is in good shape you should be fine at that rpm for extended periods of time.
     
    73cj5, Jan 27, 2006
    #8
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