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Best Gear Ratio For...

Discussion in 'The Hokey Ass Message Board' started by HD74, Aug 28, 2009.

  1. HD74
    Joined: Jan 24, 2009
    Posts: 303


    <HR style="BACKGROUND-COLOR: #d1d1e1; COLOR: #d1d1e1" SIZE=1 itxtvisited="1"> <!-- / icon and title --><!-- message -->
    <!-- BEGIN TEMPLATE: ad_showthread_firstpost_start --><!-- END TEMPLATE: ad_showthread_firstpost_start -->Ok , this is the set-up; flathead 175-200 HP, mated to 4 speed tranny with the following gears; 4.02, 2.41, 1.41, and 1.0. So the question is anyone have similar gearing, if so what's your rearend gear ratio? What's your RPM at 60 MPH? Share your experience, what do you think would be the best gear ratio, Thanks.

    This is all going in my 51 f-1.
  2. Mattilac
    Joined: Oct 27, 2007
    Posts: 1,153


    How talls your rear tire? Say its around 28" tall, and you stick a 3.00:1 gear in the rear, slightly over 2000RPM will put you at 60mph...
  3. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,906

    need louvers ?

    A simple formula for you to consider -
    MPH,times trans ratio,times rear axle ratio,times 336 =
    divided by tire hight = rpm

    So for my car it would look like:
    75mph, times .68 overdrive ratio, times 3.23 rear axle gear, times 336 =55349.28
    divided by 26.6 tire hight = 2080 rpm at that speed
    that's the best formula i've found for rear gear ratio calculation, and it's pretty damn accurate. Just figure out a comfortable rpm at cruise speed for you and plug in gear ratios until you find what you want.
  4. 53sled
    Joined: Jul 5, 2005
    Posts: 5,818

    from KCMO

  5. HD74
    Joined: Jan 24, 2009
    Posts: 303


    I've got a calculator, anyone with real world experience with this gear combo. Tires are 28.9.
  6. Dale Fairfax
    Joined: Jan 10, 2006
    Posts: 2,585

    Dale Fairfax
    Member Emeritus

    Since you have the calculator, what's the question? What R.P.M. do you WANT to be running at 60 m.p.h. (or 65 or 70?). Your Flathead will be happiest running somewhere near it's torque peak-like 2200-2500 R.P.M. so gear it accordingly. Mine's happy with a 3.78 gear and 29 " tires
  7. Periah Bon3s
    Joined: Jun 21, 2009
    Posts: 57

    Periah Bon3s

    2500 rpm @ 65 mph w/28.9" tires = 3.31 gears sounds good to me.
  8. onlychevrolets
    Joined: Jan 23, 2006
    Posts: 2,307


    my 264 inch nailhead pulls a T-5 and a 300 gear with a 26 inch tall tire . Benton Tennessee is a speed trap on hwy 411 and I can pull 5th at 35mph going through there. And it'll run 80 too
  9. If you have a 4.02 1st gear you should be happy with a 3.0 or so rear set, I run a 3.0 rear with a blown 8ba, C4,and a 36 PU with 30" Rear wheels and am really happy with it. Used to run a 36 sedan with a Sag 4sp with 3.11 1st gear and was never really happy with 1st always wanted a T56 with 3.36 or T10 with a 3.44 or anything anything taller than the 3.11, it was not very happy off the line. Espically with the heavier sedan.
    The PU cruises at 65 to 70 at around 2200 and goes way up from there
  10. HD74
    Joined: Jan 24, 2009
    Posts: 303


    I thank you all for your comments.

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