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Stock M42 for street: 3.73 or 4.10

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    #1

    Stock M42 for street: 3.73 or 4.10

    So, I got ahead of myself and started asking for any 4.10 LsD for sale but have since realized I may be better off going to a 3.73. (Thanks for the feedback on WTB btw)

    Im looking for some specific feedback from those that have experienced stock 318 with 3.73 or better yet, those that have experience with both 3.73 and 4.10.

    I have found some posts recommending the 3.73, but more related to the 325 m20, which is not a good comparison, and a lot of discussion related to autox.

    For me, I use my 318is for street only, some city, mostly highway driving (25 minute drive to work) and occasional long trips ~500 miles one way to visit family.

    Knowing a 3.73 is probably a better match for my driving style (better mpg would be nice too), I do want to make sure I'm not going to hate driving her after going to 3.73. I do enjoy opening it up now and then.

    Thanks!
    Last edited by mjimport; 01-16-2016, 06:36 AM. Reason: More
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    #2
    I think you would be happy with a small case 3.91 gear differential. It lowers the rpm's a little for freeway driving and you won't feel as much of a torque loss. With the 3.73 diff I think you would actually hurt your Mpg because the M42's rpm's would be to low and would have to work harder to move the car along.

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      #3
      go 5mph less on the highway and shift 500rpms earlier and you can keep the same economy of a 3.73 while maintaining a 4.10. Ask me how I know.....
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      BMWCCA #398608
      IG @yagayo38

      "The Best E30's were built with two camshafts four cylinders and sixteen valves!".

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        #4
        I had a 4.10 previously and now had a 3.91 and I actually notice a decent difference. Maybe it's just in my head but I definitely recommend staying with the 4.10


        Sent from my iPhone using Tapatalk
        E30 is life :finger:

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          #5
          Originally posted by getouth View Post
          go 5mph less on the highway and shift 500rpms earlier and you can keep the same economy of a 3.73 while maintaining a 4.10. Ask me how I know.....
          Agreed. I should mention that I typically shift between 3000 and 3500, and cruise around 2500, which I think is on the low side for the m42. I don't think it could stand to shift another 500 lower. Perhaps maybe when I'm 70, LoL

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            #6
            I have ran both 4.10, and now I run 3.73. I do a lot of driving on the hwy so the 3.73 is perfect. If you make long drives often, then I recommend 3.73. I have a 318is btw

            Sent from my Samsung Note 4
            '91 318i (Alpine) - daily
            '88 325ix (Zinno) - drive here and there!

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              #7
              I don't have an m42 car with a 4.10 but I have a 325iX with a 4.10 and an m42 with a medium case 3.73.

              I like the 3.73 for highway as it seems to let the car cruise along with little throttle. The only problem with the 3.73 is when I hit hills in 5th (at about 3300 rpm I'm at like 75) it doesn't have enough torque to pull me up so I either lose speed or have to downshift to get up and over.

              Also keep in mind this is regularly between 5000-7000 feet so I am losing about 3% power per 1000 feet of elevation so I am running on 15% less power than the sea level guys but my car is stripped out so it probably evens out.

              I would say i doubt you will be unhappy with either but you feel the difference in the taller gears. There isnt as much torque to turn the wheels and the just car feels slower. I rode back to back in my 3.73 318is car and a 4.10 318is (also stripped out) car and the 4.10 car felt faster to 100 mph on the highway, almost as if it were easier for the car to get there and it had more oomph at 100 mph than mine did. That being said you can hit almost 90 before having to shift out of third with the 3.73.

              It is like a 10% difference in gearing so it wont be that noticeable. At 3000 rpm on the highway in the 3.73 you will be running at about 3300 rpm in the 4.10 to achieve the same speed. Obviously at lower rpm the difference is less rpm and at 6000 rpm the difference would be about 600 rpm. Not really a huge difference unless you have the engine to turn the taller gears.
              318iS Track Rat :nice: www.drive4corners.com
              '86 325iX 3.1 Stroker Turbo '86 S38B36 325

              No one makes this car anymore. The government won't allow them, normal people won't buy them. So it's up to us: the freaks, the weirdos, the informed. To buy them, to appreciate them, and most importantly, to drive them.

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                #8
                a 3.73 with a m42 is like my 325es with 2.93. It'll be a dog but give fantastic economy.

                Stick with a 4.10 and enjoy the ride :)

                FYI If you have a 325i M20 and run a 4.10, (vs stock 3.73) you can spank stock e30 m3's

                ...true story
                If it's got tits or tires, it's gonna cost ya!

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                  #9
                  I drive 25 minutes through some hilly roads to get to work, I can see the 373 getting annoying if it can't maintain cruising speed without downshifting.

                  4.10 it is. Thank you all for the input!

                  Comment

                    #10
                    I drive 25 minutes through some hilly roads to get to work, I can see the 373 getting annoying if it can't maintain cruising speed without downshifting.

                    4.10 it is. Thank you all for the input!

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