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Thread: STR Z4 Coupe "build"

  1. #1
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    STR Z4 Coupe "build"

    We will see how she does, was running SCCA B stock with 245 40 17 v710s, but the camber limitation was just too much to overcome.

    Current set up still needs to be shaken down and consists of

    RE Rear Shock Mounts
    Ground Control Street Plates
    Koni Sports
    H&R Sport Springs
    17x8 OZ ultraleggs
    245 40 17 R-S3
    K&N Drop In filter

    Any feedback would be appreciated.

  2. #2
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    Jeff -- you will need to bag the H&R sports for something stiffer in the rear, get wider wheels and fine tune the alignment. We'll talk at the next event.
    Now in E92 M3 ZCP -- Absolute beast

  3. #3
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    I am not sure how serious this build is for STR but with the weight of the car you are going to want to run the 17x9 with 255/40/17 tires. I know they will fit on the rear but might have a little more trouble with the fronts if you dont have coil overs for more space inboard and some camber. I would highly recommend AST and Vorshlag for many of the parts you need. Motor mounts, Trans, mounts, RTAB limiters, wheel studs, and shocks / coil overs.
    Christopher
    STX 197
    1997 328is

  4. #4
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    Cool, you should have a fun time with a Z4 Coupe in STR.

    As others have said, you need 9" wheels and probably 255s. You also need to a lot "more" suspension if you are serious and want to catch the Miatas and S2000s. I'd also ditch the GC camber plates, they are noisy and not as robust as Vorshlag plates.

  5. #5
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    Quote Originally Posted by cledbetter View Post
    I am not sure how serious this build is for STR but with the weight of the car you are going to want to run the 17x9 with 255/40/17 tires. I know they will fit on the rear but might have a little more trouble with the fronts if you dont have coil overs for more space inboard and some camber. I would highly recommend AST and Vorshlag for many of the parts you need. Motor mounts, Trans, mounts, RTAB limiters, wheel studs, and shocks / coil overs.
    I would love to install RTAB limiters BUT:

    "If the Stock bushing accommodated multi-axis
    motion via compliance of the component material(s), the replacement bushing may not be changed to accommodate such motion
    via a change in bushing type, for example to a spherical bearing or
    similar component involving internal moving parts. Pins or keys may
    be used to prevent the rotation of alternate bushings, but may serve
    no other purpose than that of retaining the bushing in the desired
    position.
    "

    Given that the RTAB limiters limit the movement of the bushing, but do not serve to retain it, the SEB says this is not legal.


    Motor/transmission mounts are not necessary as the stock pieces are not compliant at all


    The issue with tire/wheel combo is not strut clearance but rather clearance with the fenderwell, and I cannot remove the liner since the SEB doesnt say its legal.

    Wheel studs are a matter of personal preference, but the stock bolts are lighter than the stud/nut combo, and really are just dress up parts that should be replaced yearly at a significant expense.


    The car was surprisingly neutral at the limit in stock class, until the tire was over-driven on the fronts due to a lack of camber (using outside quarter of the tread) and tire temps indicated such.

    As said before the car still needs to be shaken down on an autox course, but preliminary testing indicates that the relatively stiff springs in the rear compared to the front rates, in addition to the added camber (going from -.5 to -3.5 makes a world of difference) puts more grip on the pavement with a PS2 than stock configuration on a v710.

  6. #6
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    I've thought about this, but I just don't have the budget for it. Plus our cars are probably just too heavy. What do you have in mind for the diff? 9" rims should fit if you have close to a 40/42 offset. I have 17x8.5's and could easily fit a 255 in the front. Also you're going to need MUCH higher spring rates to be competitive.

  7. #7
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    Quote Originally Posted by wassup61 View Post
    I would love to install RTAB limiters BUT:

    "If the Stock bushing accommodated multi-axis
    motion via compliance of the component material(s), the replacement bushing may not be changed to accommodate such motion
    via a change in bushing type, for example to a spherical bearing or
    similar component involving internal moving parts. Pins or keys may
    be used to prevent the rotation of alternate bushings, but may serve
    no other purpose than that of retaining the bushing in the desired
    position.
    "

    Given that the RTAB limiters limit the movement of the bushing, but do not serve to retain it, the SEB says this is not legal.
    RTAB limiters limit the movement of the bushing is true but you are not changing the bushing type. You are not replacing it with a spherical bushing. You can change the bushing to whatever material you want as long as they fit in the original location and does not increase the metal content. They are legal if they are not metal.

    Quote Originally Posted by wassup61 View Post
    The issue with tire/wheel combo is not strut clearance but rather clearance with the fenderwell, and I cannot remove the liner since the SEB doesnt say its legal.
    Think you should go read 14.2.F again. Looks like you can modify fender liners to me for tire clearance and lip rolling (but cant change contour..) I had my 17x9 with 255 on my mom's Z4 coupe and think they would fit well with a roll and some camber. Her car is stock.

    Quote Originally Posted by wassup61 View Post
    Wheel studs are a matter of personal preference, but the stock bolts are lighter than the stud/nut combo, and really are just dress up parts that should be replaced yearly at a significant expense.
    Just makes my life easier changing tires all the time especially with spacers.

    I forgot to mention that some type of limited slip is going to make a huge difference on getting power down out of corners. It did in my STX 328is and you have more power than me!
    Christopher
    STX 197
    1997 328is

  8. #8
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    Friend of mine is going to stop running his Z4 in STR, he has it well prepped and is selling his parts.

    Here is the link.

    http://forums.bimmerforums.com/forum....php?t=1669933

    Joe

  9. #9
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    Too bad his LSD does not fit the Z3 as I'd be pretty interested in picking that up.
    Now in E92 M3 ZCP -- Absolute beast

  10. #10
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    OP - you ask for advice, and then try to argue with us?

    Listen to these guys, they know how to set up a BMW to win.

    Stiffer springs, may I recommend something in the 550/650 or 600/750 range.

    Stiffer bars, not sure what works on a Z4.

    Bigger wheels with 255's.

    Better camber plates and better shocks wouldn't hurt.

    You might think your driveline isn't sloppy, but when you upgrade your subframe, diff, tranny, and motor mounts, you'll be shocked at the difference.

    The biggest difference will be taking weight out of that pig. Seats, battery, custom exhaust will all help.

  11. #11
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    Team Engineer and Codriver checking in.

    It was a fun year and the budget build accomplished exactly what we wanted it to. We got a ton of seat time and determined whether it would be worth it to properly build this car, BMW tax and all. In just my 2nd year of regular autocrossing I earned 4 top ten overall PAX in 14 events locally, where we typically have around 40-60 drivers. Three of those results were top 5's and one was FTD in the rain, beating out an SM WRX by 0.5 seconds on raw time. We attended both of our first real SCCA event in Chicago on worn, heat cycled tires, and I placed 7th in a class of 12 and 52nd out of 145 overall. 2nd and 8th were separated by only 1 second, so this is a pretty close class with great competition to look forward to next year.

    Despite these successes, we were consistently about 0.5-1.0 seconds behind z3papa and a well-prepared S2000 with a good driver and codriver. The STR class in our local club is quite competitive, as one event I was 4th in class but 7th overall. With a little more driver training and a lot more car prep, we should be able to at least not DFL at a tour event next year.

    Now some comments on setup.

    255's will not quite fit with the current wheels, 17x8.5 et42 K1's. At the last event this year, the right front rubbed really hard on the inner body, enough to cause concern. And the tire is really really close to rubbing the fender, so I don't want to use spacers. Besides, over on s2ki, there is a heated debate about the crisp response and light weight of the 245 being worth it for some drivers over the max lateral grip of the 255. For the time being, we'll have to stick to 245's.

    The car now has Powerflex FCAB and Rogue RTAB, both made a HUGE difference in being able to control the car at the limit, especially on bumpy courses. Diff and trans are next on the list for bushings. We will also get the race bushings for the Rogue RSM's. At this time I cannot justify the $160 for the AST RSM's, over the $10 for Rogue race bushings.

    Now for weight. The driver seat was swapped out for the last event of the year. What a huge difference. Not only the 50lb weight loss, but in how easy it is to pilot the car. It is hilarious to watch video of the passenger moving around so much, while the driver stays put. We should be able to get it really close to min weight for the class which is 25lbs. On a grain scale the car weighed out at 2995lbs with this seat. So with the other seat and the 25lb muffler we chopped off that night, and maybe some other stuff here and there, we can get pretty close to 2900. We don't want to change out the battery due to all the electric-run components like oil pump, water pump, steering, etc... With the alternator off for the majority of the run, it would really suck to lose oil pressure because we wanted to drop 20lbs off the rear of the front-biased car.

    AST4200 with the vorshlag plates will be on order pretty soon once I nail down the rates we want. I measured the motion ratios of the springs and bars and found the front MR to be really low for a strut setup, probably due to BMW's tight packaging and the camber plates inclining the strut beyond what is usually done. I also want to drop the rear bar for weight and also to help the droop travel for the inside wheel (no $$$ for an LSD yet). Anyway, here are the MR's:

    Front shock/spring .897
    Front bar .861
    Rear spring .723
    Rear shock 1.18
    Rear bar .554

    So you can see the rear spring MR is a little higher than the commonly quoted e46 value spread out all over the forums, and the front MR is pretty low due to the strut inclinaton. With this in mind, assuming a 52/48 weight bias, 200lb driver, and 80lbs front 50lbs rear unsprung weight, I get the following wheel rates and suspension frequencies without the front/rear bars:

    500/650 is a 403/348 wheel rate at 2.26/2.22hz without the front or rear bar
    600/750 is a 483/402 wheel rate at 2.48/2.39hz without the front or rear bar

    So once you add the front bar in we'll have a bit of front frequency bias which is good. But I'm not sure I want to run 2.5hz on bumpy courses like our local place. Anyone else that speaks that language, I could use some advice.

    The car is also currently dumped to the ground which is really screwing with the rear camber both static and dynamic. So I will be measuring the camber curves to determine the ride height we want, but just to hazard a guess it will be about an inch higher front and 2 inches higher rear than it is now. Without considering correction for cross weight and F/R bias.

    Thanks for reading. Some parting photographs:






    IMG_0277 by pstynoski, on Flickr


    IMG_0320 by pstynoski, on Flickr


    IMG_0308 by pstynoski, on Flickr
    Last edited by illinipo; 01-28-2012 at 11:18 PM.

  12. #12
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    Quote Originally Posted by illinipo View Post
    80lbs front 50lbs rear unsprung weight
    Your front unsprung looks right but the rears should be in the 110-140 range.

    Top running cars on R-Comps and slicks run in the high 2's to low 3's in Hz depending on aero, I don't know how much lower you need to be on street tires but Lincoln is pretty smoth and grippy so I think you can probably be in the mid 2's.

    Rake is a lot less important for Auto-x than for track since the speeds and aero effects are lower, you might find a different set up could benefit you....

  13. #13
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    FWIW a lot of the top S2000's in the class run in the mid 2's and the local guy we have been chasing is switching from 2.1/2.2 this year to 2.3/2.5 next year (those calcs both without bars, but he is running a front and rear bar).

    Here are some numbers with the updated weights. I thought rear unsprung might be lower due to the brakes but I guess I was wrong... This is with 52/48, 2925lbs with 200lb driver, perfect cross weight :sigh:, and 80f/110r unsprung.

    500/650 is a 403/348 wheel rate at 2.32/2.30hz without the front or rear bar
    600/750 is a 483/402 wheel rate at 2.54/2.48hz without the front or rear bar

    Thanks for your comments
    Last edited by illinipo; 12-01-2011 at 11:20 PM.

  14. #14
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    You're likely to want less rear Hz than an S2000 due to the extra torque you're putting down, but yeah I'd think either of those setups should be close enough for you. I've been faster in testing with rates near your proposed high end, with a really big front bar, but I think it actually generated more grip near your proposed low end. So I plan to do some (more) experimenting next year to see if I can make the softer setup work better for me. (side bonus that it's more comfy on the street!)

  15. #15
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    Alright, thanks. To be honest I'm leaning to the 500/650 setup, it is going to be a huge change in the way we have to drive it so I would rather make an incremental change than make it a completely different car right away. If we end up going to the 2.5hz next season so be it, but maybe from a driver education standpoint we would be better off starting at 2.3.

  16. #16
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    Quote Originally Posted by murph1379 View Post
    You're likely to want less rear Hz than an S2000 due to the extra torque you're putting down, but yeah I'd think either of those setups should be close enough for you. I've been faster in testing with rates near your proposed high end, with a really big front bar, but I think it actually generated more grip near your proposed low end. So I plan to do some (more) experimenting next year to see if I can make the softer setup work better for me. (side bonus that it's more comfy on the street!)
    Softer rear springs with a rear bar is the way to go for Pro-Solos.

  17. #17
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    I miss my car.... the RTAB are rogue engineering... also... i miss my car... also rear end coming out next weekend for full bushing/mount overhaul and guibo/center support bearing replacement.

  18. #18
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    dub'd
    Last edited by illinipo; 12-10-2011 at 03:55 AM.

  19. #19
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    Getting there...


    IMG_0450 by pstynoski, on Flickr


    The center support bushing was TOAST.
    Last edited by illinipo; 12-10-2011 at 03:54 AM.

  20. #20
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    IMO the perfect car for STR, but you will need to get much more serious with the build in order to beat the S2000s; maximum performance parts and absolute minimum weight. The typical off the shelf parts aren't going to cut it.

  21. #21
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    see post 11 for details on "more serious build"

    The driver matters more than anything.

  22. #22
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    Some progress to report.






    Last edited by illinipo; 10-18-2012 at 11:03 PM.

  23. #23
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    On the 11th day of Christmas, Bimmerworld gave to me, two Group N motormounts at a massive discount!

    http://store.bimmerworld.com/2012-12...nts-p1754.aspx
    Last edited by illinipo; 12-22-2011 at 03:11 PM.

  24. #24
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    Holy cow those mounts are stiff! They came in today nicely packaged... Bimmerworld sure does know their packing tape

    We also got the inner races off the diff finally...



    The right side one gave me a lot of trouble trying to do it alone. Needed one guy on the fire and one guy on the chisel. But once we got about 1/8" of gap between the race and diff, they popped right off with an A/C clutch puller pushing on a bolt/washer over the axle stub hole. Here are two threads about e46 and newer diff DIY if anyone is into that kind of thing.

    http://www.e90post.com/forums/showthread.php?t=365404
    http://www.e90post.com/forums/showthread.php?t=513544

    Now patiently awaiting the Wavetrac. And a truly monumental Tischer order. And a visit to AKG for a chat and some bushings. And a season's worth of R-S3 from Tirerack. And a little order from Rogue. And a BIG order from Vorshlag
    Last edited by illinipo; 10-18-2012 at 11:03 PM.

  25. #25
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    You know the wavetrac is a gear-type, right? I'd cancel that order and replace it with a gear type. Call performance gearing or diffsonline. The gear type will have essentially the same performance of an open diff in an autocross application.

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