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Engine RPM at 60 MPH?

Discussion in '1965-1970 Shelby Mustang GT350 & GT500' started by Edward66GT350, May 22, 2005.

  1. Edward66GT350

    Edward66GT350 Well-Known Member

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    I'm doing 3100 rpm's at 50 mph and 3700 rpm's at 60mph. Is this correct for 3.89 rear gears? Seems too high for freeway cruising. Any suggestions?
    Thanks
     
  2. KenG.

    KenG. Well-Known Member

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    That sounds about right. That is also why most people are putting 5 Speeds now. I did when I had my GT350, and on a 67 I am building I will also do the same.
     
  3. Early67

    Early67 Well-Known Member

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    Mine might be off a tad, but I can double the first two digits of the rpm reading and that'll be close to my mph. ie, 3500 rpm ~ 70 mph
     
  4. Edward66GT350

    Edward66GT350 Well-Known Member

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    Early67,
    What gear ratio does the rear axel have?
     
  5. DJR

    DJR Well-Known Member

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    Sounds kind of high for 60 MPH. With 3.91 in my B9 in 4th gear I turn about 3000 rpm. Keep in mind tire size plays a role.
     
  6. Edward66GT350

    Edward66GT350 Well-Known Member

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    DJR,
    Exactly right re tire size. I'm running 215 or 225 60 series. I think I need a taller tire. Any suggestions?
     
  7. Early67

    Early67 Well-Known Member

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    3.89.....stock '67 GT350
     
  8. BillH

    BillH Well-Known Member

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    That sounds more like 4.57 gears. Assuming the tire height is 25.5"
    3100 RPM = 51.5 MPH
    3700 RPM = 61.4 MPH

    For 3.89 gears, I get:
    2600 RPM = 50.7 MPH
    3100 RPM = 60.5 MPH
    3600 RPM = 70.2 MPH

    I know I want a 5 speed. Need to put that aluminum T-10 in storage.
     

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