Torsional rigidity test: 67 coupe

Discussion in 'Classic Mustang Specific Tech' started by mustbereel, Oct 7, 2007.

  1. How do the outer rails tie into the car?
  2. The outer rails are welded to the flange at the bottom of the rocker panels.
  3. With all the heim joints, the TCP braces can only aborb push/pull forces along their length. That is of course the main job of these type of reinforcements and that's what gives the main contribution to the strength, but I don't really see the point of making a brace that's free to pivot in all directions. I mean, you don't make a roll cage with heim joints either. Even though the strenght comes from the triangulation, the welded connections also contribute a little.

    The factory Export brace also resists upward forces a little, due to the W shape of the arms. When I installed one on my car, I had to lenghten my home made Monte Carlo bar by an inch. That tells me that the Export brace also forms a very stiff "V" and that it takes a lot of force to pull the shock tower ends towards each other.

    The TCP Monte Carlo bar also attaches rather far from the shock tower (in a more flexible area), rather than just in front of the tower like a conventional one.
  4. mustbereel: I now have just one question. Did you finish the backyard, yet?
  5. With 3 Mustang projects at once I bet you know the answer to that question. The deck is falling apart and trees are dying. The yard can wait. Anyone know where I can find a 69 fastback project car?
  6. More tests

    I've just finished installing and testing all of the new braces. These include the firewall to frame braces, export brace style diagonals, jacking rails and rear seat divider.

    I also cutout and made a custom firewall since the last test. This is to allow me to move the big 4.6 DOHC back as far as possible. It looks real clean too.

    Testing method is the same as before. Place car on three jackstands, sit on 10ft bar mounted to the MII A-arm mount and measure deflection at the right front corner where the frame meets the radiator support.

    New baseline: 0.44"
    Install and weld in braces from firewall to subframe: 0.42". I expected more.
    Weld braces in previous step to aprons and weld shock tower repair panels: 0.41"
    Install export brace style diagonals: 0.36" Big improvement but I expected more.
    Bolt in SFC. 0.36" like last time, no benefit to torsional rigidity.
    Weld in SFC. 0.36"
    Bolt in SFC X-brace. 0.36" Do these do anything?
    Weld jacking rails to outer rocker panels: 0.35" That's all?
    Add steel rear seat divider (screws, will weld later): 0.31". Definately worth it.

    Just for kicks I moved the 10ft bar back to the radiator support to compare with my orginal tests: 0.40". That's better than the best combo before (0.475") but I had neither the rear seat divider nor the jacking rails last time.

    Bottom line: it's more rigid now than with any combination when the shock towers were still there. I suspect that with the addition of the rear seat divider and jacking rails there would be little difference between stock and MII arrangements.

    Reinforcement braces and repair panels welded in. The braces have aditional structure to provide a mounting point for the export brace style diagonals.

    New firewall, repair panels and diagonal braces.

    Rear seat divider. 16ga steel screwed in for now.

    I don't have any more modifcations to test until I install the IRS. I'm open to testing other ideas this weekend before I dismantle the setup. This is assuming it's something I can fabricate easily and it's reverseable.

    Attached Files:

  7. the next thing you should try is solid welding all the panels instead of just relying on the spot welds or doubling the amount of spot welds. either way i think you'd be very surprised at the results.
  8. where your front shock tower brace goes, you might want to use some steel welded to the side panels to layer the stresses better
  9. you might think about taking the rear seat divider into a sheet metal shop and have some ribs rolled into it. even if it didn't add any to being rigid it would not act like a big bass drum.

    jake, i am the new guy :)
  10. It would be interesting to see how much difference it makes. I'll sleep on it but right now I'm pretty tired of welding.
  11. It's kind of hard to see in the pictures but where the braces attach there is a piece of 10ga steel that is welded directly to the frame reinforcement tubing. The whole structure is very strong and the idea is that the load is transfered directly to the frame and not the inner apron pannels. Without this structure and the firewall to frame tubing there would be nothing for the export braces to push against when loaded.


    In this picture you can see some of the metal behind the aprons. At the cowl I have reinforced the attachment point with a 10ga. angle.

    Attached Files:

  12. Hi Jake,

    Wecome to Stangnet and thank's for the suggestion. I plan to use Dynamat or something similar to dampen any bass drum effect.
  13. Suprised because it doesn't change at all?
  14. newer unibody cars have about three times the spot welds an old mustang has and they are much stiffer. that was one of the old T/A tricks to stiffening up the unibody as well. it will make a big difference.
  15. A few more tests this morning.

    To help isolate the remaining flex I repeated an experiment from my last round of testing. I moved the right rear jackstand from the rear spring mount to the front spring mount. This effectively eliminates the back 1/3 of the chassis from the test. Last time I did this I was amazed at the difference and achieved a best (least) deflection of 0.35". With the same setup, but with all of the new mods in place, I measured 0.19". This means I've reduced flex forward of the front leaf spring mount by about 45%.

    Next I removed the sfc x-brace 0.19". Still no noticeable difference.
    Then I removed the steel rear seat divider: 0.23". Wow. About a 20% change.
    Since I have to remove the seat pans to move them back and lower them I thought I would see if they made any difference: 0.23". Nothing.

    I don't recommend removing the seat pans completely because they do reinforce the floor for the weight of the occupants.

    Seam welding will have to wait until another time because I've dismantled the test rig for now. Time to clean up and rest for work tomorrow.
  16. Apples to oranges. I contend that the newer unibody cars are stiffer, but NOT because of the number of welds.

    I recognize T/A teams did it. I don't think it matters for a non track car that doesn't have to conform to an obscure rulebook.

    I'll bet you a dollar ($1 US) it will not make a big difference. How much improvment (in %) do you consider a 'big difference'?

    Here is some seam welding tech:

  17. now, let's make what i'm talking about clear here. i'm talking about seam welding or doubling the spot welds in pretty much the entire car, not just a couple places. i'd consider a "big difference" between 5 and 10% maybe more.
  18. The rear seat divider is a better deal then: 13% improvement and you can make it on a rainy afternoon.
  19. I made a summary :)

    The improvemens in % are the relative changes compared to the previous step, so the for the Export Brace: (0.64-0.48)/0.64 = 25%


    Baseline 0.66"
    Factory crossmember 0.64" 3%
    Export Brace 0.48" 25%
    Monte Carlo bar 0.48" 0%
    Passenger torque box 0.48" 0%
    Subframe connectors 0.48" 0%
    Subframe X brace 0.475" 1%


    Baseline 0.67"
    Cut shock towers 0.69" -3%
    MII cross member 0.63" 9%
    Subframe connectors 0.63" 0%
    Subframe X brace 0.61" 3%


    Baseline 0.62"
    rear mounting point forward 0.52" 16%
    front mounting point rearward 0.35" 33%

    Baseline 0.44"
    Firewall to subframe braces 0.42" 5%
    Weld braces to aprons and
    shock tower panels 0.41" 2%
    Diagonals ("Export Brace") 0.36" 12%
    SFC 0.36" 0%
    SFC X brace 0.36" 0%
    Jacking rails 0.35" 3%
    Rear seat divider 0.31" 11%

    Baseline 0.35"
    rear mounting point forward 0.19" 46%
    Removed SFC X brace 0.19" 0%
    Removed seat divider 0.23" -21%
    Removed seat pans 0.23" 0%
    Front mounting point forward 0.40" -0.74%

    Most effective changes

    Export Brace 25%
    Diagonals 12%
    Rear seat divider 11%
    MII cross member 9%
    Firewall to subframe braces 5%
    Subframe X brace 3%
    Factory crossmember 3%
    Jacking rails 3%
    Weld braces to aprons and
    shock tower panels 2%
    Monte Carlo bar 0%
    Passenger torque box 0%
    Subframe connectors 0%

    It's interesting to see that the simplest mods seem to have the greatest effect. But, as mentioned before, one should keep in mind that although some mods showed little to no improvement in this particular test, it doesn't necessarily mean that they are therefore worthless.
  20. I guess so too, because that's a 16% improvement and the rails and seat divider were a 14% improvement.