Torsional rigidity test: 67 coupe

Discussion in 'Classic Mustang Specific Tech' started by mustbereel, Oct 8, 2007.


  1. mustbereel

    mustbereel Member

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    Summary

    Thanks for the excellent summary Helmantel. With all the tests it was kind of hard not to get lost along the way.

    Even though some components added nothing to torsional rigidity I'm sure they help in beam strenght. The only part I have little confidence in is the SFC x-brace. It didn't add anything in my tests and I can't see it adding very much to beam strength. I think the idea is sound but it just doesn't seem to work.
    #81
  2. ron67fb

    ron67fb Founding Member

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    It works by lightening your wallet. I myself don't see how it would help in any way. It seems that the floorpan is already doing what the X-brace should be.
    #82
  3. Jimmys66

    Jimmys66 Founding Member

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    I'm sold on the rear seat divider. It will get added to the project list.

    I would have never thought there would be that much improvement.:nice:

    I kinda feel like I'm muching off your results. I don't have the time or the welding skills to do anywhere near your testing, so it's nice to see what works and what doesn't. I really don't want to cage this car so anything I can do helps.

    I would have been upset not to get any real results from the aftermarket bracing, since most of us are on a tight budget anyways. The money could go to well needed places.

    All I can say, is from one very appreciative stangneter, thank you for your time. :hail2:
    #83
  4. 68conv4sp

    68conv4sp New Member

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    Superb Thread! Question: do the coups have the same stock divider set up (panel or lack there of) behind the rear seat? I ask because my vert has a steel panel immediately behind the rear seat that is clearly stock. It comes up about 3/4 of the way to the top of the seat back. Is that in the same plane as the aftermarket add on?
    #84
  5. CraigMBA

    CraigMBA New Member

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    The pannel in your convert is missing in the coupes.
    #85
  6. C0V3R

    C0V3R Member

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    With the rear seat divider, were you using screws or tack welds when you made the measurements?
    #86
  7. blkfrd

    blkfrd Member

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    I have not been following this post until now. When I bought tank armor for my car, the guy told me that some group of oval course racers from some foreign country (can't remember which) liked the tank armor for the added benefit of stiffening the rear of the chassis. When I installed mine, I first welded in 1" x 1/8" steel flat stock all around the gas tank opening and then redrilled the gas tank holes. Then I used grade 8 bolts to install the gas tank and tank armor. It would be interesting to see what kind of improvement that tank armor makes to the chassis.
    #87
  8. mustbereel

    mustbereel Member

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    I used screws (about 16) so I could pull it out. I will probably weld it in place when I'm ready for it.
    #88
  9. mustbereel

    mustbereel Member

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    Since I don't have the gas tank in I could put it back and check before and after. Although not as substantial as the tank armor if the stock gas tank makes any improvent I think the tank armor would only add to it. It will be a while before I'm back to testing. I have to fabricate something to mount the IRS before I get back to testing.

    Keep the suggestions coming.
    #89
  10. SN65

    SN65 New Member

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    Very interesting stuff here. Very similar to our study. Here is my two cents worth on the topic.

    I have been studying a bit of data covering the structural analisys of a NASCAR chassis.

    A lot of it applies to unibody construction.

    For example. The major chassis members are...

    The rockers and central cross brace (on a unibody the rockers and the seat pan that runs from rocker to rocker) are the major lower structural members.

    They tie from the rockers to the frame rails with structural tube. (Torque boxes on a unibody)

    Then they have the frame rails front and back with a cross brace at the front and rear suspension mounting points. That is it for the chassis.

    The major torsional members in order of sensitivity to torsional loads translated from NASCAR to unibody are

    1 the roof structure that runs from the "A" pillars at the windshield to the "B" pillars behind the drivers door.

    2 The strut towers and any reinforcement that runs from the tower to the firewall at the "A" pillar.

    3 The "A" pillars themselves.

    4 The front frame rails from the firewall to the core support.

    5 The rockers and the torque box structure.

    6 The structure at the top of the windshield.

    7 the structure at the botom of the windshield or cowl area.

    8 the frame rail extension that runs from the firewall to the seat pan structure.

    Addressing these 8 areas is where the best bang for your buck will be in reducing torsional deflection.

    I find it interesting that, under torsional loads, the area under the greatest stress is the roof structure at the edge of the roof just over the side windows.

    Of course if the "A" pillars and other areas of the car are not correctly reinforced none of the loads will transfer to the roof, etc, etc, etc...

    We have just about finished all of our modifications (sans roll cage) and we have reduced torsional deflection (applying 750 lbs to the front suspension mounting point) from 1.33" to just over 1/8".

    Bob
    #90
  11. SN65

    SN65 New Member

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    Here is what we have done so far.... The green shows the original structure. Everything else is a modification.

    [​IMG]

    [​IMG]

    Bob
    #91
  12. bnickel

    bnickel Founding Member

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    nice Bob. :nice: how are thefir and ice cars coming along?
    #92
  13. C0V3R

    C0V3R Member

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    One thing I was curious about - do you think adding a series of ribs (similar to the inside of an aircraft) down the floor pan side to side including the transmission tunnel would make a big difference? I would think its effect would be like the seat pans.
    #93
  14. Blue Oval Man

    Blue Oval Man Member

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    As for adding strength to the roof sides from the A pillars to the B pillers, as well as along the top of the windshield and down the A pillars themselves, do you think filling the channel with one of those structural foams like is used in some of the newer luxury sedans would be of any benefit? I do not mean one of those insulating spray foams like you get at Home Depot, but true automotive structural foam.
    #94
  15. C0V3R

    C0V3R Member

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    BOM I toyed with that idea too. It would probably help even more if you did the whole roof and put a laminate sheet on the other side.

    I think a lot of the problem is in the joins at both front and rear pillars more so than in the beams themselves. Just look at where mustangs develop cracks in the paint
    #95
  16. Blue Oval Man

    Blue Oval Man Member

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    I Have no personal experience with the structural foam, just the little I have read about it but it seems if the A pillers and side structure were solid it would probably help where the body joins also.
    I don't know if this would be possible, but could you add a U type channel across the roof from B pillar to B pillar, and another from the B pillar to the opposide A pillar, on each side, therefore creating an X, and fill this with the structural foam? Could this act as a sort of "cage", adding strength and rigidity while still staying under the headliner for a stock look?
    I know this would not be as strong as a true tubular roll cage, but it could be an option for a more stock appearing application. Just throwing some ideas out there.
    #96
  17. bnickel

    bnickel Founding Member

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    structural foam in the windshield pillars and the rocker panels should greatly stiffen the structure, probably the frame rails as well but i'm sure you'd see the same benefit in the rails. i know a lot of 4x4 guys use the structural foam to stiffen up the chassis of their rigs and it also helps to prevent rust as well. i think i would have the car chemically stripped with an alkaline solution before filling anything with foam though just to be on the safe side to help prevent rust from festering. ultimately i'd like to have my car chemically stripped and then EPDM primer dipped and then do the foam stuff but that could get real expensive another alternative could be to have the inside of the rails and stuff powder coated after stripping, i understand this is actually possible now.
    #97
  18. SN65

    SN65 New Member

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    Hi BOM,

    Adding structural foam will increase the strength of the individual item, unfortunatly, the major issue is the joint or connection between the "A" pillar, the roof and the cowl structures. To improve this area of our cars, we are adding gussets between the cage and the existing "A" pillar, cowl and roof structures . Also, if you look at our layout, you will note that we have added additional cage bracing at the roof and "A" pillar intersection.

    Bob
    #98
  19. freddiecougar

    freddiecougar New Member

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    OK, here's a question...wouldn't this all be changed dramatically by having a motor/trans bolted in the car? It's not like it is a stressed member of the chassis, but it would appear to be something like a triangulated brace...bolted to both sides of the engine compartment and the center of the car under the trans tunnel.
    Am I missing something?
    #99
  20. mustbereel

    mustbereel Member

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    I see your point but since all the mounts are flexible I don't think it will add much. I may test this when I test install the engine (soon). If the engine was mounted with a block plate then I think you would see a large improvement.

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