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Thread: STR Z4 Coupe "build"

  1. #26
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    The Wavetrac has a preloading clutch that activates in high differentiation situations (like freewheeling). So that is not quite the case. Besides, that is all that fits the budget right now, and every clutch type LSD I have ever driven in autocross, I hated.

  2. #27
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    Quote Originally Posted by illinipo View Post
    The Wavetrac has a preloading clutch that activates in high differentiation situations (like freewheeling). So that is not quite the case. Besides, that is all that fits the budget right now, and every clutch type LSD I have ever driven in autocross, I hated.
    A correctly setup clutch type lsd will be far superior to a gear style diff, the problem is that almost all clutch lsd's are built for roadrace and are far to aggressive for auto-x.

    Main difference is the decel characteristics, in a rr diff you want stability off throttle but in auto-x that causes push. I know Blanton knows what works for auto-x with an E46 diff.

  3. #28
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    The main problems I've had is with the ramps and preload, just way too aggressive. Rather than limiting slip of the inside, the ones I've driven just make the outside spin up when you get the inside spinning. Resulting in instant backwards racing.

    So if I were to get a true LSD it would have to have tunability in the shim/clutch stack and preload springs, like the Giken offers. I really don't want to bother with buying complete case units for top dollar and having to pay freight to send it out all the time for tuning. I just want the diff itself (I can do the R&R) that is tunable.

    There is also budget, a true LSD is not in the cards right now. Maybe next year if we dont like the wavetrac.
    Last edited by illinipo; 12-28-2011 at 10:58 AM.

  4. #29
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    Quote Originally Posted by illinipo View Post
    The main problems I've had is with the ramps and preload, just way too aggressive. Rather than limiting slip of the inside, the ones I've driven just make the outside spin up when you get the inside spinning. Resulting in instant backwards racing.

    So if I were to get a true LSD it would have to have tunability in the shim/clutch stack and preload springs, like the Giken offers. I really don't want to bother with buying complete case units for top dollar and having to pay freight to send it out all the time for tuning. I just want the diff itself (I can do the R&R) that is tunable.

    There is also budget, a true LSD is not in the cards right now. Maybe next year if we dont like the wavetrac.
    I totally agree.

    I know in the past wavetrac was looking for some people to showcase their products (might have been for their Porsche parts), you should call them directly and tell them what you're doing, might help your budget

  5. #30
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    I think we have to beat the S2000's first!

  6. #31
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    I totally agree, whatever diff you get, it's important to work with a builder who understands autocross and what it needs in a diff. My initial diff settings were way too aggressive, as you've experienced, but I've worked with Jim to get it where I need it.

    If you're comfortable doing the install work, that's a huge advantage for you, sounds like it'll save you a bundle of cash!

  7. #32
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    The diff isnt that bad at all. I think I have about a half hour in it so far for full teardown, if you don't count being an idiot about the right side inner race for an hour.

  8. #33
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    Quote Originally Posted by murph1379 View Post
    I totally agree, whatever diff you get, it's important to work with a builder who understands autocross and what it needs in a diff. My initial diff settings were way too aggressive, as you've experienced, but I've worked with Jim to get it where I need it.

    If you're comfortable doing the install work, that's a huge advantage for you, sounds like it'll save you a bundle of cash!
    Murph -- what did you start with and what did you finish with.
    Now in E92 M3 ZCP -- Absolute beast

  9. #34
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    Really not totally sure, unfortunately. I'm still looking for a bit less off-throttle lockup, but it was much better on-throttle in 2011 than in 2009/2010.

  10. #35
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    Well, probably the only way to have less off throttle lock with your current diff would be to reduce the decel ramp wich is much more difficult and expensive than to increase ramps. I did it to one of the ZF diffs I built but my machinist did not like doing it as a one off and charged me for it!!!

  11. #36
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    Whats wrong pete you don't like my m-spin diff?

  12. #37
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    I don't think it likes me either... 3 spins in 4 runs ugh

  13. #38
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    Quote Originally Posted by illinipo View Post
    Rather than limiting slip of the inside, the ones I've driven just make the outside spin up when you get the inside spinning. Resulting in instant backwards racing.
    How in the world is a passive device like an LSD going to stop a wheel without traction from slipping? At best all it can do make both wheels spin at the same speed. It is not going to help a driver trying to apply more torque than the available traction.

    It seems like it should be rather simple to grind the backside ramps square to convert a 2-way LSD into a 1-way LSD.

    Last edited by MatthewH; 12-30-2011 at 10:44 AM.

  14. #39
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    Quote Originally Posted by MatthewH View Post

    It seems like it should be rather simple to grind the backside ramps square to convert a 2-way LSD into a 1-way LSD.

    To make things work right and last you need to cut new ramps rather than grind the old ones, not all that easy to do with the material the compression rings are made out of.

  15. #40
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    Quote Originally Posted by illinipo View Post
    I don't think it likes me either... 3 spins in 4 runs ugh
    blame cold temp, run flat ps2s, but never question the \\\marketing division. Soon I will have some fun parts... you should come up to help with my valve adjustment since jeff seems to have a habit of btm-dropping anything and everything into the engine bay lately. Not to threadjack

    a pic from summer:



    how you like that bb image compression bitch!

  16. #41
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    Quote Originally Posted by MatthewH View Post
    How in the world is a passive device like an LSD going to stop a wheel without traction from slipping? At best all it can do make both wheels spin at the same speed. It is not going to help a driver trying to apply more torque than the available traction.
    This is exactly why I prefer torque sensing, torque biasing differentials.

  17. #42
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    But when you lift a rear wheel, then all the torque goes to the wheel in the air, and instant backward racing. I also know that you don't have to hop curbs to get the inside rear wheel in the air. Thus Torsen's are poor substitutes for a properly set up Salisbury.

  18. #43
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    Quote Originally Posted by Z3racer701 View Post
    But when you lift a rear wheel, then all the torque goes to the wheel in the air, and instant backward racing. I also know that you don't have to hop curbs to get the inside rear wheel in the air. Thus Torsen's are poor substitutes for a properly set up Salisbury.
    This past season with the open diff in this car I basically never spun on corner exit. It was always very progressive and controllable. So no, not instant backwards racing, like it was with the three other cars I drove this season that had true LSDs. The two torsen cars I drove were predictable like the open diff, but better because I could get on more power, sooner, without losing it.

    And the wavetrac has a preloading mechanism for high differentiation. Like a wheel in the air. That is I think the third time I said this in this thread. I appreciate the suggestions, but please read before you regurgitate the internet at me

    Quote Originally Posted by Z3racer701 View Post
    But when you lift a rear wheel, then all the torque goes to the wheel in the air
    And this is a common misconception, there is actually NO torque applied in that situation.

    Also, another thing the internet doesn't seem to get quite right along those lines is that an open diff actually sends equal torque to both wheels at ALL times. It does not "send all the power to one wheel."

    It is all about available traction with TBD's. If you know how to make them work, they can work for you. You do not need to break a wheel loose in order to use its full potential.

    On the flip side, the only thing that an LSD seems to be able to do is overcome the outside wheel's available traction. Plus, it is much less controllable and predictable because it operates on differentiation rather than sensing the available traction. That is, you have to lose traction in order for the LSD to work. In autocross, you may lose traction without anticipating it because of the uneven surface... so it can be a very bad thing if your diff is too aggressively ramped, preloaded, or locked.
    Last edited by illinipo; 12-31-2011 at 01:24 AM. Reason: Automerged Doublepost

  19. #44
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    The gear based LSDs also send no torque to both wheels if one is lifted. Only clutch-packs (and viscous) are going to send any (and all) torque to the non-lifted wheel. Though if your RWD car is lifting a rear wheel on acceleration you certainly have other problems (or you have it setup like a gocart and don't need any differential.)

    I am very pleased with the performance of my factory clutch-pack LSD for autocrossing. The 2-way "problem" can be completely avoided with left-foot braking. Anything that would actually engage the LSD on deceleration on course is most likely a less than ideal driving technique regardless.
    Last edited by MatthewH; 12-31-2011 at 09:27 AM.

  20. #45
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    Quote Originally Posted by MatthewH View Post
    The gear based LSDs also send no torque to both wheels if one is lifted.
    Here, read this if you don't believe me. The Wavetrac has a preloading hub between the side gears so it does not suffer from the zero torque situation.

    http://www.wavetrac.net/technical.htm

  21. #46
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    Quote Originally Posted by MatthewH View Post
    I am very pleased with the performance of my factory clutch-pack LSD for autocrossing. The 2-way "problem" can be completely avoided with left-foot braking. Anything that would actually engage the LSD on deceleration on course is most likely a less than ideal driving technique regardless.
    I agree that the stock diff is fine and a $2.5k diff is overkill for local auto-x and HPDE's bottomline is, if you want to win a national championship in either roadracing or auto-x the stock diff will hold you back.

  22. #47
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    Quote Originally Posted by illinipo View Post
    On the flip side, the only thing that an LSD seems to be able to do is overcome the outside wheel's available traction.
    By LSD you mean a clutch-type? (since a gear-type is an LSD too) Like we've been saying, there are some that are set up well, and others notsomuch. I've never had a problem with outside wheel traction, even when my diff was set up much too aggressively, had more problems with push.

    You've said you were a FWD guy, maybe that's why you've had so much trouble driving RWD cars? Can't just mash the "go" pedal with the steering wheel turned and expect a good outcome. Gotta be smooth.

    Maybe the wavetrac will let you do this? I dunno, hopefully it works well for you, we're just trying to share what's worked for us. You'll note all the STR miata and S2000 guys that have stock gear-type diffs moving to OS Gikens, they're not doing that for their health...

  23. #48
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    At this point I have WAY more experience in RWD than FWD. And believe it or not, FWD is not as simple as point and shoot A properly set up FWD car will drive just like a RWD car. You have to be even easier on the throttle since the driven wheels are turning, too.

    I don't think I've yet said the wavetrac is better than a clutch LSD. The ONLY reason we chose it is it is the lowest cost non-open diff. Nothing else fits in the budget right now.

    The gear-type does not actually limit slip so they are properly termed TBD or ATB but definitely not LSD.
    Last edited by illinipo; 01-02-2012 at 11:57 AM.

  24. #49
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    Why not an OS Giken?

  25. #50
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    Please read... cost is the problem with any of the clutch type differentials since tuning would be costly. This is a never done before unique setup so we are tryingthe least costly route first

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