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M6x differential ratios?

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    M6x differential ratios?

    My m62 swapped e30 is running a 5 speed box from a 530i. The current differential is a s2.93 and I'm still pulling 3800 rpms and 80mph. I feel this is a bit high for prolonged periods of time. I guess I will have to opt for a 6 speed transmission in the future to bring down the rpms. Anyone else running high rpms at highway speeds?
    1987 325i-M60b44 swap

    #2
    I think if you did a 6 the gears might be too short. Have you considered a different diff?

    edit, first in a 6 might be useless if you go that route.
    Originally posted by wholepailofwater
    Q
    :devil:


    WTB: Dove Grey e36 Front Door Panels (2 door)

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      #3
      Have you counted turns on that diff? 3800 @ 80, even with a 1:1 5th doesn't line up.
      2006 GMC Sierra 2500HD 4WD LBZ/Allison
      2002 BMW M3 Alpinweiß/Black
      1999 323i GTS2 Alpinweiß
      1995 M3 Dakargelb/Black
      - S50B32/S6S420G/3.91
      1990 325is Brilliantrot/Tan
      1989 M3 Alpinweiß/Black

      Hers: 1996 Porsche 911 Turbo Black/Black
      Hers: 1988 325iX Coupe Diamantschwartz/Black 5spd

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        #4
        Yeah, that's not correct. Your speedo is wrong, your tach is wrong, or you do not have a 2.93. What are you using for tach calibration?

        With a 2.93 and ZF320, 80mph is 2700 rpm's in 5th.

        A 4.10 diff would have you at about 82mph at 3800 RPM's.


        Also, to the other posters point, the Getrag 420g and ZF320 have the exact same gearing for the first 5 gears, the 420g just has an additional .82:1 overdrive gear.
        Last edited by JGood; 03-28-2017, 04:10 AM.
        85 325e m60b44 6 speed / 89 535i
        e30 restoration and V8 swap
        24 Hours of Lemons e30 build

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          #5
          I'm rolling the 6 speed with a 3.24, and I'm running at about 3k at 75 IIRC....
          I agree with Jgood, something is off....
          Dumpster Fire Pilot

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            #6
            Solved!

            Originally posted by nrubenstein View Post
            Have you counted turns on that diff? 3800 @ 80, even with a 1:1 5th doesn't line up.
            Yes. I made sure to double check the diff tag and manually count the rotations when I pulled the rear subframe.

            Originally posted by JGood View Post
            Yeah, that's not correct. Your speedo is wrong, your tach is wrong, or you do not have a 2.93. What are you using for tach calibration?

            Originally posted by delamaize View Post
            I agree with Jgood, something is off....
            Bingo. Jgood nailed it on the head. Double checked my speed via gps on the way home, all good. When and check the Dakota Digital Rpm signal converter that hasn't been touched in a year (so I thought). Input set for 8cyl, output set for 7 cylinders! I don't know why I didn't think of this as getting bumped in the glove box, especially with us wiring and swapping ecus.

            So thank you Jgood(again) and everyone else that answered. I feel like an idiot but sometimes you need a second opinion. Rpms are much lower now. Thinking I should be around 3k at 80mph. Now I glad I didn't sell my S3.25 diff so I can install it.
            1987 325i-M60b44 swap

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