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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    The main problem with a structure that is "too" stiff is that instead of the energy of the collision being absorbed by the crush zone it is passed on to the occupants. This means there is more energy for the secondary collision - you and the steering wheel or shoulder belts, etc...

    To this end SN65 hasn't extended anythinig past the shock tower.
    Reem made his strut so that it will bend in a frontal collision.
    My strut ends just forward of the front suspension.

    A strut that reaches all the way to the front of the frame would be stronger but it also eliminates the "crush zone" although I don't think it was engineered as such in 1964.

    The idea is to survive the collison, not save the car.
     
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  2. bnickel

    bnickel Founding Member

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    exactly what i was talking about. no, there was no crush zone engineered into these cars originally however, by ending the reinforcements at the shock tower or just forward of it or using a curved down bar, mounted in such a way that it deflects the impact away from the chassis, like a curved down tube that reaches al the way to the front but is welded at 45 degrees or so to the frame rail so that the impact will, in effect, deflect outward from the car and down.

    personally i wouldn't add the tubes any further forward of the shock towers, now keep in mind we are talking about a car with shock towers, not a car with a MII type suspension which needs the down bars all the to the front of the frame for stability and strength that is lost by removing the shock towers.

    by the way, i have very rarely seen a frontal collission on an early mustang where the impact weny much further than the shock towers and the ones that did had the front frame sections bent down after the towers, so whether it was engineered that way or not there is some, not a lot, but some crush area to these cars, unfortunately it's the main are we're trying to strengthen here, so we need to put that back somewhere, so just move it forward of the towers
     
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  3. lauras70mach1

    lauras70mach1 Member

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    Didn't later years have a notch in the front aprons that was supposed to help the apron collapse on impact?
     
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  4. 70vert

    70vert New Member

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    Extremely ugly/quickly drawn proposed SN65+Reen combo

    Hey all,
    Please critique the attached (ugly, crudely drawn) image. The shock tower outer cover/spring cover would be a thicker material than stock. The tube drawn in red would go straight through the shock tower and would most likely be tubular and inserted through a circular hole cut with a same-diameter hole saw through the coil spring cover then welded around that hole once it is in place.
    Not sure how the SN65 tubes behind it would end up looking or attaching to this tube. I ended it just forward of the shock tower to minimize concerns about crush zone. I added the down tube from the junction just behind the shock tower since I have a convertible and have no roof to support the structure, so I need to attach to as much sheet metal as practical.
    The tube could be curved up front or cut and welded in sections, whichever is cheaper to fabricate. Front attachment would be boxed in around the frame rail. Rear attachment would be a solid plate with a corner bolted or welded through the frame rail on one side and on the other side extended to the to the vertical tube SN65 has there. This plate would help tie frame to rockers around that corner and the whole structure tied into a bunch of sheet metal would be a cowl shake killer and shock tower reinforcement.
     

    Attached Files:

    #144
  5. 01ragtop

    01ragtop Member

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    I'm no engineer so keep that in mind with my response. I grabbed a piece of tubing and bent it in a similar shape to your picture and looked for weak spots. (not real scientific I know) I seems like to me it will put stress on the shock covers, and as you noted you would beef them up pretty good, but I think I would add a connection to the down tube both front and back at the bottom of the shock cover or maybe a little lower if possible as well. This would stiffen it up a bit more as well as give it more support. With mounting it low on the firewall you will give it a lever to pull away from and push toward the top of the shocks. You probably already have it, but a monte carlo bar would be a must, and I would use grade 8 bolts to mount your new shock cover. (not sure what they were stock)

    You might even consider tying in the down tube to a sn65 style bracing as well.

    Again I am no engineer!
     
    #145
  6. mustbereel

    mustbereel Member

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    70vert,

    Don't worry about the drawing it's still effectively shows your idea.

    I doubt the tube running from the shock tower to the torque box will add much more that extra weight. Instead I would use that extra weight to reinforce the area aft of the firewall. All the extra reinforcement in the front is just going to pass the stress down the line.

    If you haven't already done so go to http://www.sn65.com/Fire & Ice unibody reinforcement.htm and really study the chassis modifications they've made. They've done far more testing than I did and found that the original convertible structure worked better than adding subframe connectors. They just modified that structure a few places such as tying the front subframe into the seat pan reinforcements. Of course you're working without a roof so full length subframe connectors tied into the original convertible reinforcements can't hurt.
     
    #146
  7. 70vert

    70vert New Member

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    01ragtop, thanks for going and bending a piece of tube just for the idea, hope you didn't go to a lot of trouble and hope you can use that tube for something! I do have a MC bar and a Boss 302-style crossmember and, after the engine is installed, plan to go with either a Maier-style export brace that goes over the engine or a Global West with an additional custom piece going over the engine. I am not convinced that the stock export brace does as much work as it could be doing attached to a thin piece of sheetmetal. The way SN65 (by way of a square bar or Global West (by way of attachments through firewall) reinforce their connections to the firewall seem more effective. With a crossbar like Maier's and a reinforced connection to firewall my tube may be overkill, but the main reason I want it to send the force down the line, as mustbereel observed.

    Mustbereel, that's exactly what I'm looking for! :D I've read SN's stuff pretty extensively on C-C.com and on the Fire and Ice builds. The way my car feels now, as a convertible with a stiff rear end, subframes-through-the-convertible-floor type of ride, is that everything is rigid except for the shock towers, cowl, and everything ahead of the firewall basically. Jacking up from the rear, the same side front comes right up, but when I hit a pothole with my front left tire, say, the entire front end shakes and throws the suspension off. That's what I'm trying to avoid. I'm trying to:

    •Strengthen the cowl/firewall area - SN65 has paved the way here!
    •Provide a more direct attachment of the shock tower to the rockers and subframe connectors - the twin spars that add strength to the floor and are connected midspan with the convertible subfloor. Important since I don't have a roof.
    •Spread the load across more frame rail and send the load over to the other shock tower with help of the Maier-style brace in addition to the MC bar. I believe that the frame rail twists under load from one shock tower (think of the leverage from top of shock tower) and giving it some extra help from elsewhere on the rail and the rocker/cowl/subframe area may help. Or I might end up with a square plate tearing off from the rocker. In which case I KNOW it's doing something and a bigger plate goes in there. :D

    I'm sensitive to weight, but if you took a ride in my car you'd be able to see what I'm up against as far as front end shake not harmonizing with the rest of the car. :nonono:
     
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  8. 01ragtop

    01ragtop Member

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    Oh crap! I just re-read my post and I see the confusion. I didn't bend a piece of tube in the same size and diameter that you would be using. The fenders just happen to be off my car so I took some vague measurements and made a smaller piece of tubing to scale or as close as I could. I am sorry for the confusion this is completely my fault.

    I got the idea from a post over at the C-C forum where a guy made a model of the vintage mustang body. I have tried to find it again to post in this thread, but have not had any luck.

    Again very sorry for the confusion.
     
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  9. bnickel

    bnickel Founding Member

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    do a search on BossBill, he made that post, it was a few years though, so it may not be available anymore.

    70 vert, i think what you may be experiencing is actually bumpsteer and not as much cowl shake as you think. i had the same problem with my 69 coupe and it was mostly due to the cracked shock tower, once the crack was fixed it no longer did the front end shake. what shake it did have left was mostly removed by the roller perches and the small amount that is still there is entirely bump steer, in my case there isn't much because the ride height of the car is only slightly lower than stock, maybe 1/2-3/4 inch.

    before you go and do all that chassis reinforcement I'd highly suggest spending a few bucks to get the parts to measure the bumpsteer on your car and use those adjustable Steeroids tie rods to remove as much of it as possible. once you have that done you can then decide just how much "cowl shake" you have left.

    you might also consider adding one of the shelby style rollbars with a good tie-in to the chassis to help with some of the torsional twist you were speaking of as well as TCP style subframe X-brace. another thing you might consider is adding a GW type jacking rail/rocker reinforcement kit too, if you're going to do all the other reinforcements.

    and don't underestimate that Boss 302 shock tower brace mod i spoke of earlier. it gets welded into the "trough" in the shock tower under the UCA.
     
    #149
  10. 01ragtop

    01ragtop Member

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    Thank you. I found it.
     
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  11. development1

    development1 New Member

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    Is it possible to get the measurements and angles for the bars from the firewalls to the frame rails?
     
    #151
  12. 65wildstang

    65wildstang Member

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    mustbereel, I've been reading over this older thread for awhile now and wondering how your car came out. I plan on doing a mini tub shortly and need alot done as far as chassis stiffening while we have it in the shop. My major drawback is the car is already painted , so we will be limited to what we can weld to. We have already welded in the tinman sfc's and I was looking into the x brace. I don't see why we can't add the torque boxs without issue? I will definetly be adding the panel to the back seat as recommended. I am open for everyones suggestions on this topic. Thanks
     
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  13. mustbereel

    mustbereel Member

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    Has it really been five years since I started this thread? To look at the car, you wouldn't think so. Alas, I haven't had much time to work on it. I've also changed directions a few times, opting to sell the Terminator and replace it with a stock 2007 4.6l. I've made slow progress on the fuel, AC and braking systems but very little else. Notice four years of dust on the new paint.

    [​IMG]

    Before you make any other changes, I recommend researching convertible rockers and related structural components (including torque boxes). Since you are already planning a mini tub and torque boxes, this is a great time to tie everything together. The rockers can be added without affecting your exterior paint and will probably be the best improvement you can make. If I could start over, that's the one change I would make.
     
    #153
  14. 65wildstang

    65wildstang Member

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    I am trying to keep from welding on the lower rocker pinch weld. I'm worried the heat from welding will transfer through and cause the paint lift or crack on the outside of the rocker where it is seen. I actually thought about welding everything on the inner rails except the lower area and bond it with adhesive. I agree the rockers and torque boxs definetly are needed. Just trying to see how the best way of going about it is. Thanks
     
    #154

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