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3:73 in a US 5 speed?

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  • 3:73 in a US 5 speed?

    Anyone here ever ran a 3:73 diff with an OD 5 speed?

    Plugged in 3.83, 2.20, 1.40, 1.00, 0.81 into a few
    calculators using 4.10 and 3.73 w 225 50 15's.
    Reason I am asking is to me 1st and 2nd seem
    pretty short / come up pretty quick.
    I did search, and most felt it would be a "downgrade"
    Just curious if anyone here has actually tried this on an M3.

    Thanks!
    Last edited by NSXM3; 05-14-2007, 03:08 AM.

  • #2
    No, b/c it is a downgrade.

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    • #3
      What are you optimizing for?

      The E30 M3 has never been about starts from a stoplight; it's about 2nd through 4th gear.

      The only reason i can see to make that swap would be to improve your gas mileage.
      Seattle, WA
      currently:
      1988 M3, ex j-stock
      1984 911, RoW 3.2
      1990 Peugeot 205 GTI 1.9
      http://cars.g93.net

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      • #4
        I have that diff in my car with an OD tranny. Purely by numbers, it should theorically make the car slower on tracks because it doesn't accelerate as much as with the 4.1, but in fact it can be more properly geared for slower corners where the 2nd gear and 4.1 diff can otherwise lead straight into the rev limiter, while the longer 3.74 diff allows to keep the revs down and keep full acceleration in 2nd gear, not requiring to upshift to 3rd and its lowere revs.

        This weekend, there was another M3 at a track event, and specific corners were more favorable to the 3.74 diff allowing to keep 2nd gear, while my friend had to go to 3rd and ended up getting slower.

        To sum it up, it is great on highways as the engine is less buzzy, but it depends on which track you drive.
        Last edited by LeeVuong; 05-14-2007, 04:47 AM.


        [email protected]

        1969 2002 racecar
        1989 M3 racecar
        e39 Touring

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        • #5
          I just put in a 4.45 if that tells you anything

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          • #6
            I get it...........
            Just not used to having a 1st gear that feels like a granny gear.:lostme:

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            • #7
              do whatever you think you will like. if you don't like it you can always change it back. the car will still be awesome with 3.74 gears and you may love it even more like that. i say go for it. i also agree with leevuong.

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              • #8
                LeeVuongI have that diff in my car with an OD tranny. Purely by numbers, it should theorically make the car slower on tracks because it doesn't accelerate as much as with the 4.1, but in fact it can be more properly geared for slower corners where the 2nd gear and 4.1 diff can otherwise lead straight into the rev limiter, while the longer 3.74 diff allows to keep the revs down and keep full acceleration in 2nd gear, not requiring to upshift to 3rd and its lowere revs.

                This weekend, there was another M3 at a track event, and specific corners were more favorable to the 3.74 diff allowing to keep 2nd gear, while my friend had to go to 3rd and ended up getting slower.

                To sum it up, it is great on highways as the engine is less buzzy, but it depends on which track you drive.
                Give it a shot, you got nothing but money to lose.:ha:


                I know on certain turns I runs out of gears and rev to the moon, like just before west bend at Lime Rock or Down the laces of the boot at the Watkins. Wrong place to shift up then down.

                I guess it would make first something more useful than a smoke em out of the hole gear.

                Bet you'd see 30mpg at 70 in 5th...

                Any one run one 3.74 at either of the tracks mentioned with a 2.3 and taller gears?


                Where would the power band be with those gears? I'd assume it's gotta narrower since it requires more torque down low. Downshifts below 4K to keep it in the sweetspot is my guess.






                Hmmph, interesting thread.

                Comment


                • #9
                  I had that diff in my E30 M3. It was horrible. I drove another E30 with the stock 4.10 and it felt like it had another 30hp. I immediately went out and bought a 4.10 to replace the 3.73 that was in the car and it feels 10x better.

                  To give you an idea how slow a US E30 M3 is with a 3.73, when I test drove my car I hadn't driven an E30 M3 in more than a year and I thought it was dog slow. Turns out it was the 3.73 diff. If I can tell a difference even without a reference point, you know that the car is SLOW.

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                  • #10
                    What's the top end with the 3.73???
                    1988 Diamantschwarz



                    "The original M3 is utterly brilliant in ways the people at M have either forgotten about or choose to ignore."

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                    • #11
                      It all depends on what you are tuning for. I want to see how much better I can make the highway MPG over 70 mph. I didn't buy an M3 to drag race, and I want to cut noise and revs at speed. Before I install the 3.73 I have, I am going to Dynamat the trunk and rear seatback. If that gets it to point I can hear my kids trying to talk to me from the back, I might leave the 4.10 in, but as an experimant, it's a pretty cheap one.

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                      • #12
                        At 70 mph, with 23.5" tires (225 50 15's) you will drop about 300 RPM
                        at 70 mph from the 4.10. It was a good idea, but not what I am looking for.
                        Here is a very simple caulculator.
                        Many to choose from on the net.
                        http://www.richmondgear.com/streetcalculators.html

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                        • #13
                          Originally posted by NSXM3 View Post
                          At 70 mph, with 23.5" tires (225 50 15's) you will drop about 300 RPM
                          at 70 mph from the 4.10. It was a good idea, but not what I am looking for.
                          Here is a very simple caulculator.
                          Many to choose from on the net.
                          http://www.richmondgear.com/streetcalculators.html
                          That calc seems screwy! Enter 4.1 for the diff on the left side, enter the numbers it gives into the right side and it says you have a 3.32 diff!

                          Anyway, it looks like about a 6-7mph difference at a given RPM in 5th. Mine will be in this weekend if all goes well, and I'll letcha know what it's like. Might suck, but I won't know 'til I try it.....

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                          • #14
                            That is a very simple example.
                            The one on the right is using 1to1 as a final drive
                            rather than .81

                            Here is another, page down to RPM
                            Looks the same, 70 MPH.
                            4.10 with a .81 OD = 3324
                            3.73 with a .81 OD = 3024
                            http://2.3liter.com/Calc1.htm#RPMInGear

                            Cant find my old favorite, will keep looking.......
                            Your right on the 6-7mph. 6 mph at 3000 RPM.
                            Your tire size also plays an important role here.......
                            (Also I may have gooFed a bit. Have been using 3.73 where it might really be a 3.74)
                            Last edited by NSXM3; 05-21-2007, 02:37 PM.

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                            • #15
                              "What's the top end with the 3.73???"

                              At 7000 RPM with 23.5" 225 50 15's a 3.73 in 5th (.81) would be 162mph, 4.10 = 147 MPH.

                              Not sure my M3 is ready for that!

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