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    LSD vs Open Diff

    Considering an LSD for the M140i for Supersprints/Time Attack events but the BMW Luxury tax is expensive in these things.

    Looking at Queef around $4k.

    Do they really improve Lap times or just make it easier to achieve consistency?

    Smooth, early, progressive throttle input is obviously the goal exiting corners, but in theory seems much harder to achieve for the average amateur driver with an Open diff.

    Even braking with slight steering input seemed more controllable with a better rear diff tying the rear end down in previous LSD swaps I have had done.

    Exiting corners now I find I have to get on and off the throttle at corner exit with one wheel spinning. It's possible to get it perfect, just more difficult.
    Attached Files
    BMW M140i daily. Honda Odyssey family car.





    Wakefield 1.07.386 (FG Falcon - Street Tyres 1.08.8) Marulan Short FG Falcon 43.4 SMP GP FG Falcon 1.48.1 Winton FG Falcon 1.35.4

    #2
    I fitted Quaife's to both my cars, not because I like the Quaife specifically, but because there is no other option, they are the only LSD available for the Jags.

    Fucking expensive, but worth every cent, in my opinion anyhow.

    I can't give you a direct comparison with & without LSD on the track, but last year I had the unique opportunity of two more or less identical cars side by side, same tyres, same engine tune / power, just one with a Quaife, one with the stock open diff.



    So there was a chance to road test them back to back a few times, and wow the LSD makes a huge difference on the street (in these cars).

    With the open diff, in left turns, the inside (left) lights up with anything more than gentle throttle, then the DSC kicks in which makes you go no-where, so you turn off the DSC and then you are just single pegging everywhere.
    With the Quaife you can actually accelerate through a left turn, without the DSC intervening, or not nearly as much.

    So with the Quaife you can leave the traction control / DSC on, it is far less intrusive, which makes a huge difference in how the car moves, and you still have the safety net of DSC should you push it too far.
    You'd hope a new BMW has a smarter DSC system than the ~2006 system which is in these cars, so may not be such a noticeable improvement, I don't know.
    Presumably the M140i is the same setup as the M240i, which i have driven, not on the track though, but I did find it to be a bit of a letdown, the DSC intervention being part of that let down.

    I'd say putting an LSD in can only make it better. If that better is worth $4k in the M140i I couldn't tell you, but it was in my cars.

    Are there any other options apart from Quaife for this BMW?
    Jaguar XJR, Freelander 2 HSE, Jaguar XKR, MINI Cooper S
    Originally posted by nutttr
    People must assume you are some sort of drug dealer with all these nice cars turning up to a fibro home

    Comment


      #3
      In terms of pure lap time, itís prolly no more than a 0.5s improvement, but youíll enjoy it a shitload more.
      Japanese Nostalgic Car - Dedicated to classic japanese cars

      Comment


        #4
        As far as your lap times as above a touch quicker but the big difference I find is knowing that the rear end is going to act 100x more predictably in the even that the arse steps out. Being able to steer on the throttle and know you'll have positive drive is worth the money in itself. Nothing worse than having it step out and then start to single peg and snap back.

        For a M140i. I wouldn't hesitate. Would I chuck a $4k in a $4k car ? Nah.
        - Gary

        97 Mitsubishi Lancer Coupe 1.8 (cheap and cheerful motoring)
        16 Honda Grom (MSX125) Snail racing would be faster

        Comment


          #5
          I'd be mighty tempted to run a spool/minispool/welded up diff for a while.

          Comment


            #6
            As above, I think you will find it noticeably quicker and a lot more fun. That was the case with the Yellow Peril, but we used a Cusco one way.

            If you are baulking at the $$, Roadsailingís idea of a spool or CIG Locker isnít a bad alternative. If you go down this route, LMK and Iíll give you some pointers on how to set up the suspension to address the shortcomings.

            Comment


              #7
              Originally posted by Roadsailing View Post
              I'd be mighty tempted to run a spool/minispool/welded up diff for a while.
              Minispool or CIG Locker can be a bit of a handful on a wet road in DD mode ............

              OP - be aware that a Quaife will single-spin when one rear wheel is off the deck ... better to use a KAAZ or WaveTrac (if they are made for your vehicle)

              Comment


                #8
                From me, a big no to a CIG locker/minispool

                As to which type of LSD ? All I can say is that the ZF cam and pawl in my F1 rear end is not something I'd recommend.
                " Racing cars don't have doors. Toilets have doors" : Keke Rosberg

                Comment


                  #9
                  What's the reasoning behind these being open diff as standard?
                  Originally posted by E-Z
                  If TK told me to close my eyes and bend over, I would.

                  Comment


                    #10
                    Originally posted by Panda I give no fuck View Post
                    What's the reasoning behind these being open diff as standard?
                    LSD (Clutch pack type) was not an option for the early M140i's from BMW factory prior to purchase.
                    Reasoning was German logic to distance the M-lites from the proper M cars in terms of performance.
                    BMW M140i daily. Honda Odyssey family car.





                    Wakefield 1.07.386 (FG Falcon - Street Tyres 1.08.8) Marulan Short FG Falcon 43.4 SMP GP FG Falcon 1.48.1 Winton FG Falcon 1.35.4

                    Comment

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