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  1. #1
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    Performance Package Availability

    FYI


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    A few preliminary thoughts...

    As I expected, BMW has chosen to use the tried and true approach of a strut brace and tower reinforcement plates to help prevent deformation. While a fully triangulated brace would have been preferable, BMW's brace appears to directly address the frame deformation issue in the area most likely to be affected. While I haven't seen the installation details, I believe the brace will be attached to the exposed box frame rail, not to the tower itself. Since this is the part of the frame which can be bent, this makes perfect sense to me. Please note that the pictures supplied with the announcement have the brace against the tower and I think this is incorrect. The large hole on the mounting plate should provide clearance for the air box mount. To prevent deformation of the tops of the towers, BMW has come up with a substantial (read unbendable) shock tower mount coupled with a reinforcement plate to be installed on top of the tower. Based on my experience with the Dinan caster plates preventing tower deformation, this approach should be more than adequate. Also, as an added bonus, I believe the two pieces will act as a compression sandwich when bolted together and this should flatten out some of the bulging on affected towers. All in all, looks like a good fix to me. I plan to install the brace but will most likely retain the Dinan plates instead of using BMW's. Grease Monkey

  3. #3
    Michael
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    Re: A few preliminary thoughts...

    GM I have a few questions;

    Are there Dinan castor plates for the rear as well?

    How much did you say the ride height was affected?

    If they are planning to rivet the Monte Carlo bar into place, wouln't the rivets need to be drilled each time accecss is needed to get to the upper plenum or air intakes?

  4. #4
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    Re: A few preliminary thoughts...

    The brace is not riveted to the frame. Holes are drilled, then riveted nuts are inserted. So basically the nut is fixed to the frame by riveting.
    The brace is then attached to the frame/nut using torx screws.

  5. #5
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    Re: A few preliminary thoughts...

    Rear suspension does not have caster because the wheels can't be steered, so there are no caster plates made for the rear. The Dinan caster plates for the front raise the ride height app. 1/4" in the front only. As dwz8 said, the "rivets" referred to in the description are captive nuts which are pop riveted into place in the frame tube to provide threaded holes to bolt the strut into. This is a common practice when you don't have access to the back side of a bolt/nut combination and your Z8 already has quite a few of these.Grease Monkey

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    My Dealer says there are 42 Packages available!

    [IMG]

  7. #7
    malibujack
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    National Freze on Performance Package

    Just when we thought it was all over BMW NA thow us another curved ball, they have now put a National Freeze on the distibution of the Performance Package.

  8. #8
    Tristan
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    I was told the same thing by dealer!


  9. #9
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    Re: National Freze on Performance Package

    My Dealer has mine and he is installing it tomorrow or Wednesday.[IMG]

  10. #10
    Tristan
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    Before

    ...your dealer drills holes in your frame to install the PP, I suggest making sure the "freeze" is not because of some problem with the PP or that a newer PP addressing some concerns of owners is not coming out. Just my thoughts.

  11. #11
    FWK-Z3
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    Let me guess

    This was done by the same guy that designed the cup holder

  12. #12
    FWK-Z3
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    I see some real problems with this

    A strut brace is a good idea; howevre this design has some real problems. It does not act directly on the struts, but is offset and tansfers the load from the strut through the sheetmetal of the strut tower.

    The problem addressed by strut braces is that in their absence, there is nothing holding the strut towers apart, except where they are welded into the inner wheel housings. Because the towers are angled, there is a transverse force pushing them in towars one another when they are loaded. This puts the welds holding them to the car in tension, which could cause failure. At the very least, the strut towers can be defoemd ineward.

    Th usual design of a strut brace attaches directly to the upper suspension mounts and holds them at a fixed distance to one another -- reducng the tension on the chassis welds and preventing inward deflection.

    The problem I see inthis design is that the strut brace does not attach directly to the upper suspension mounts, but to the front face of the strut tower. This causes (1) the suspension loading to be transferred to the brace from the upper suspension mount through the relatively weak spring tower, and (2) a bending moment to develop between the suspension mount and the spring tower (the spring tower will react to a load by trying to twist inward at the rear seam. Furthermore, the attaching plates do not appear to have a bearing surface. The load is transferred by pure shear through the rivnuts - a very small area and in a hole prone to elongate.

    Wht is needed is a formed surface, such as a yoke around the top portion of the strut tower, and a brace from the rear of the strut tower attaching to the transverse bar as close to its centre as possible to eliminate the twisting moment.

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    Re: Before

    I just received the following from my Dealer:
    A BULLETIN CAME OUT TODAY ABOUT THE NATIONAL FREEZE ON THE PART.BMWNA IS REVIEWING THE INSTALLATION INSTRUCTIONS.
    I HAVE THE PART BUT I WOULD FEEL MORE COMFORTABLE ABOUT THE INSTALLATION IF THE INSTRUCTIONS WERE APPROVED BY NA.
    (IT'S FUNNY THE PARTS ARE ON FREEZE AND I HAVE THE ONLY ONE IN THE COUNTRY! HOW MUCH DO YOU THINK I CAN GET FOR IT ON EBAY?...
    ONLY KIDDING!!)
    I WOULD PREFER TO WAIT ON THE INSTALLATION...WHAT DO YOU THINK?
    LET ME KNOW.
    I chose to wait. I will keep you all informed. [IMG]

  14. #14
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    BMW has us by the "short and curlies"....

    .....this is the fix....for better or worse. Your assessment of the design make sense to me (but I'm no engineer). However, I'm guessing BMW knows how to make a strut brace and this is, I'm assuming, the best they could do. Given the space constraints, etc., I'm hoping they selected the best option that was feasable.

  15. #15
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    ...please wait....

    ...the freeze is there for a reason. Bill S. told me they have 2 things to do. 1) get the installation instructions in english, and 2 ) make sure they can install properly.

  16. #16
    Grease Monkey
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    Re: I see some real problems with this

    Your analysis is very thorough but let me make a few points. The force transmitted to the strut towers by the suspension is parallel to the suspension's travel. That is why the tops of the towers tend to bulge out around the strut mounting point. BMW's answer is to reinforce the tops of the towers to prevent this deformation from occurring and I believe their new Performane Package parts will accomplish this goal. However, because the suspension has camber and caster built into it, the suspension's travel is not purely vertical. It also has a centerline component (camber) and a rearward component (caster), though these are minor compared to the vertical component. As a result, forces transmitted by the suspension to the strut towers will not only push the towers up but also push the towers towards the car's centerline and towards its rear end. It is this force component which has led to frame rail deformation and the resultant ill-fitting body panels. Now, on the Z8, the rear inclination is greater than the centerline inclination so the best way to counteract the forces acting upon the towers (besides reinforcing the tops) would be to brace the tops of the towers from the firewall. Unfortunately, there does not appear to be a practical way to accomplish this given the location of the air plenum. The same goes for a brace connecting the tops of the two towers in a straight line. Just no room for it under the hood. Another option would be to brace the towers from the front of the car but there really isn't anything with adequate structural integrity there and because of the towers' angles of inclination, this approach would be much less effective. So that leaves BMW's method which attaches a cross brace to one of the frame rails on each side of the engine compartment. The beauty of this approach is that the cross brace is attached directly to the part of the frame most likely to deform since it is the weakest part of the tower support system. The frame rail on the other side of the tower is much more substantial. My guess is, when BMW analyzed the situation, particularly the narrowing panel gaps near the front of the hood, they zeroed in on this particular frame rail since the fenders are directly attached to it so any movement would cause them to shift. As I have stated previously, a triangulated brace (tower top to tower top and tower top to firewall) would be more effective but given the circumstances involved, I believe BMW's engineers came up with a very clever solution to the problem. As far as the brace lacking a bearing surface is concerned, please remember that most top mounted strut tower braces also lack a true bearing surface and rely on the strut mounting bolts to resist movement through shear. Frankly, given the multiple attachment points and the horizontal orientation of the cross brace, I think BMW's brace will be more than capable of resisting the forces involved. Now, your suggestion to add top braces attached to the cross brace has merit and might be worth pursuing but it does present a few problems. There is no direct route to connect to the middle of the cross brace so it would most likely have to be attached towards its outer edges where its ability to resist the tower's movement would be limited by the strength of the brace's attachment flange, definitely not the strongest part. This approach would also require some adjustability in the brace to accomodate tolerance differences from one car to another due to the multiple attachment points and this introduces complications along with the weakness of junction points. So where does that leave us? I believe BMW's engineers have done a thorough job of analyzing the problems involved and have come up with a practical solution. They are certainly in the best position to do so and until proven wrong, I see no reason to doubt their work.

  17. #17
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    !Great postings!


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