differiential gear ratios - NCRS Discussion Boards

differiential gear ratios

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  • Charlie R.
    Expired
    • July 7, 2010
    • 6

    differiential gear ratios

    I just pulled the dif out and rebuilding it. Trying to decide which gear to use, choices are 3.08 or 3.36.
    Its a 4-speed, 230 horse 1960 corvette
    any thoughts out there
  • Dan M.
    Expired
    • March 6, 2009
    • 157

    #2
    Re: differiential gear ratios

    Close ratio or wide ratio 4 speed?

    Comment

    • Charlie R.
      Expired
      • July 7, 2010
      • 6

      #3
      Re: differiential gear ratios

      1960 was a wide ratio, I believe. 3 gear in 4 speed is the same as 2nd gear from 3 speed

      Comment

      • James O.
        Very Frequent User
        • November 1, 1985
        • 160

        #4
        Re: differiential gear ratios

        i was curious as to why you are choosing such tall gear ratios. i think the the lowest used in corvettes in those years was 3:55 or 3:70. i have a 3:08 in my 270hp 1959 and it cruises well but acceleration kind of suffers. i am considering changing to 3:70.

        Comment

        • John H.
          Beyond Control Poster
          • December 1, 1997
          • 16513

          #5
          Re: differiential gear ratios

          Charlie -

          All T-10's through 1961 were close-ratio transmissions (2.20:1 first gear), which is why they came with 3.70 axles. A base 283 with that transmission and a 3.08 or 3.36 axle will make you wish you hadn't changed it.

          Comment

          • Joe L.
            Beyond Control Poster
            • February 1, 1988
            • 43221

            #6
            Re: differiential gear ratios

            Originally posted by John Hinckley (29964)
            Charlie -

            All T-10's through 1961 were close-ratio transmissions (2.20:1 first gear), which is why they came with 3.70 axles. A base 283 with that transmission and a 3.08 or 3.36 axle will make you wish you hadn't changed it.
            John and Charlie------


            I agree. A 3.36:1 is an absolutely wonderful rear gear ratio but not for a 283 with a close ratio 4 speed. As a matter of fact, not even for a 283 with a wide ratio 4 speed.
            In Appreciation of John Hinckley

            Comment

            • Charlie R.
              Expired
              • July 7, 2010
              • 6

              #7
              Re: differiential gear ratios

              thanks guys, but 50mph at 3000 rpm just wasn't working for me. 6;70/15 tires.
              trying to get better highway performance. I'm also taking off the bias ply tires, I want to drive the car much more than the guy I bought it from

              Comment

              • John H.
                Beyond Control Poster
                • December 1, 1997
                • 16513

                #8
                Re: differiential gear ratios

                Originally posted by Charlie Rossley (51944)
                50mph at 3000 rpm just wasn't working for me.
                Charlie -

                Calculator says you've got a 4.56; pretty unusual combination with a 283/230.

                Comment

                • Duke W.
                  Beyond Control Poster
                  • January 1, 1993
                  • 15671

                  #9
                  Re: differiential gear ratios

                  You have a couple of other options. The ratio set in the T-10 can be changed to wide (2.54, 1.89, 1.51, 1.00:1) by installing the later WR clutch gear and countershaft.

                  The other option is to install a new WR Super T-10 - 2.64, 1.75, 1.34, 1.00:1.

                  Either way, with a 3.36:1 axle you get an overall first gear that is about the same total reduction as the CR with a 3.70 axle with a top gear that yields fairly relaxed highway cruising - about 2550 revs at 60 MPH with tires that have the same 760 revs/mile as OE.

                  Duke

                  Comment

                  • Tom P.
                    Extremely Frequent Poster
                    • April 1, 1980
                    • 1814

                    #10
                    Re: differiential gear ratios

                    As mentioned, you CAN obtain a much more hiway compatable rpm range, but to do so will render your car NCRS incorrect.
                    So, you kind of have to decide whether you want correctness-----------or practicalness.
                    As mentioned, you can change the internal gears in your T-10 to convert it to a wide ratio, which will work better with a 3.08 or 3.36, or conpletely replace the tranny with a later wide ratio T-10 (or even a Muncie ).
                    I have a wide ratio Muncie and 3.08 posi in the 56, and I wouldn't change back for anything. I enjoy driving it both in town and on the Interstate. For the lower speeds in town, the 3.08 is often too much gear, so I simply compensate by shifting into whichever gear is more compatable.
                    With the 3.08 in the 56 and 225/75R15 radials, at 76mph the rpm is 3000.

                    Also, I feel that a 3.08 or 3.36 would not be a problem in an early Vette with a 283. Remember, the FULL SIZE Chevys with low perf engines got a 3.36 in 57 and then the 3.08 in 59. So, a somewhat lighter Vette should be just fine with a 3.08 or 3.36, even with a base 4bl 283.
                    Last edited by Tom P.; November 9, 2010, 11:47 AM.

                    Comment

                    • John F.
                      Extremely Frequent Poster
                      • March 23, 2008
                      • 2408

                      #11
                      Re: differiential gear ratios

                      Tom, Would a 3.08 be good with the base 3-speed and 250 hp?

                      Comment

                      • Tom P.
                        Extremely Frequent Poster
                        • April 1, 1980
                        • 1814

                        #12
                        Re: differiential gear ratios

                        Yes, it should be fine---------------PROVIDED----------the 3sp isn't the close ratio version. As far as I know, all of the base (or regular) 3spds had a 2.94:1 1st gear which was considerably lower than the wide ratio 4spds.

                        Comment

                        • Donald H.
                          Extremely Frequent Poster
                          • November 2, 2009
                          • 2580

                          #13
                          Re: differiential gear ratios

                          I to am rebuilding my differential. I am using Tom Parson's instructions and installing an Eaton posi unit.

                          I also plan to use 3.08 or given this discussion maybe a 3.36. I don't plan to cruise at 75 MPH, but I would like to be able to crusie at 65 and be taching at say 2,500.

                          I am also rebuilding the T10. It looks like the cluster gear to go to wide ration is about $185 at D&L. So, is it worth the $185?

                          How does a close ration tranny first at 2.20 and say a 3.36 rear compare to a 2.54 first and 3.08 rear as far a low end performance?

                          Also, is there a formula to calculate speed with the various options?
                          Don Harris
                          Current: 67 convertible Marina Blue L79
                          Former: 60 Red/Red, 2x4, 245hp (Regional and National Top Flight 2013), 66 coupe Nassau Blue, L79 (Chapter and Regional Top Flight 2017)

                          Comment

                          • Duke W.
                            Beyond Control Poster
                            • January 1, 1993
                            • 15671

                            #14
                            Re: differiential gear ratios

                            Overall reduction = trans ratio x axle ratio
                            Revs @ 60 = 760 x axle ratio (assuming you have OE revs per mile tires)

                            It's easy to set the whole thing up on a spread sheet to make a gear chart.

                            Duke

                            Comment

                            • Donald H.
                              Extremely Frequent Poster
                              • November 2, 2009
                              • 2580

                              #15
                              Re: differiential gear ratios

                              Originally posted by Duke Williams (22045)
                              Overall reduction = trans ratio x axle ratio
                              Revs @ 60 = 760 x axle ratio (assuming you have OE revs per mile tires)

                              It's easy to set the whole thing up on a spread sheet to make a gear chart.

                              Duke
                              So if I understand this correctly for overall raton:

                              close ration tranny and 3.36 rear = overall 7.4 (2.20 x 3.36)
                              wide ration and 3.08 rear = overall 7.8 (2.54 x 3.08)
                              Original for my 1960 close ration and 3.70 = overall 8.1 (2.20 x 3.70)

                              Is there enough of a difference between the 7.4 and 7.8 as far as low end driveability to make changing from close ration to wide ration worthwhile?

                              For RPM:

                              3.08 @ 60 = 2,340 (760 X 3.08)


                              Duke, where does the 760 number come from?
                              Don Harris
                              Current: 67 convertible Marina Blue L79
                              Former: 60 Red/Red, 2x4, 245hp (Regional and National Top Flight 2013), 66 coupe Nassau Blue, L79 (Chapter and Regional Top Flight 2017)

                              Comment

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