The "Mustang II" IFS Real Info & Debate Thread

Discussion in 'Classic Mustang Specific Tech' started by reenmachine, Sep 17, 2007.


  1. 69gmachine

    69gmachine Member

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    Question for those of you with the Boss 302 manual: Are any of the structural mods applicable to a street car, or does it pretty much have to be a gutted race car? I might get a copy if there's something I can use, but I have a very clean and complete interior I don't plan to part with.

    Rather than just speculate, how about a real life comparison of some different suspension designs in real street legal cars. In order to keep a level playing field, we need to try to get cars that are similar dimensionally (67-70 body styles) with full interiors, DOT tires, registered, inspected and insured to drive on the street.

    I think we need at least two volunteers who have different MII mods to square off against a more stock 67-70 with simple upgrades such as open tracker bolt on perches, and also try to get as many of the different complete set ups as we can get together: Air Ride, Total Control, Unique Performance, Global West, RRS, etc. and any brave souls who have designed their own suspension such as myself. The goal would be to evaluate the suspension, not the driver, so we would either have to swap cars and average everyones lap times, or use a handful of seasoned drivers and average their lap times.

    I'm in the final stages of getting my car back on the road but my funds are extremely limited at the moment so if anything goes wrong (I rebuilt the tranny myself) I'll be sidelined for a while. I may be counting my chickens before they hatch, but assuming I can get my car on the road sometime next week or so, I'm willing to drive anywhere east of the Missisippi, and from Tennesse to the north. It would be more of a learning experience than an all out competition with the goal of determining how well the MII design hangs with other designs in a real street car. We could also (attempt to) compare things like cost, installation, and ease of maintenance. I suspect that if the cars are similar dimensionally (including weight) that no one design will dominate in a street car, but there's really only one way to find out.

    Anyone up for a challenge?
    #81
  2. Cobra5.0Jeep

    Cobra5.0Jeep Member

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    i am not sure the moroso will fit on my 532 :(
    #82
  3. bnickel

    bnickel Founding Member

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    the only thing i can think of in the boss chassis guide that wouldn't be applicable on a street car would be the cage install. pretty much everything applies. especially if you have stock type steering, you can use the boss crossmember mod that keeps the LCA eccentric from moving around and the the LCA mount too for that matter.
    #83
  4. rbohm

    rbohm Founding Member

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    that is what i was going to say. and with a little ingenuity, you can even keep the ability to adjust the camber setting from the lower control arm if you like. just use the same pro motorsports kit designed for the 65-66 stangs.
    #84
  5. bnickel

    bnickel Founding Member

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    if you get the Cobra Automotive or Delta Bay boss style crossmember they are still fully adjustable.
    #85
  6. lauras70mach1

    lauras70mach1 Member

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    How is the Mustang II "shock tower" different from the stock shock tower? Is that too basic a question?:shrug:
    #86
  7. reenmachine

    reenmachine Active Member

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    It's really no different in principle, just about a foot shorter. This difference somewhat changes the way the loads are carried by the car though, which is what sparked this discussion.
    #87
  8. mrmustangman357

    mrmustangman357 Member

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    Has anyone considered the possible twisting effect (as viewed looking directly at the frame rail) it may have on the frame rails? considering the stock setup has the moment higher and more in-line with the rail, and with export braces etc providing support against whatever moment it has, and the MII has the forces at a farther moment arm to the frame rail (spaced outboard of the frame), with the crossmember as support. Any ideas?
    #88
  9. reenmachine

    reenmachine Active Member

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    The steel is so thick and so well supported/gusseted that I see absolutely no area for concern.
    #89
  10. jbuening

    jbuening Member

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    Out of curiosity, do you have any engineering education? I am a structural engineer, which is why i'm asking as you seem to know a bit about statics. It seems that you are concerned about the torsional effects on the frame rails considering all of the force from the suspension is applied on the frame rail. The supplied MII crossmember prevents/eliminates any torsional fatigued caused by the suspension loads. And to you guys bickering about if the shock towers/cowl take any load, yes there is a triangulation effect on these cars but the actual forces are likely not very high in comparison to the loads placed on the frame rails. The forces from the spindle to the upper shock mount are not vertical, so there is some torsion applied to the original frame rails. Torsion is also resulted from the location of the mounting points of the upper and lower control arm. This torsion will cause your shock towers to deflect inward, which is where the export braces come into play. They are to provide some support to prevent excess deflections. Unfortunately they aren't the best solution in two-piece form, which is why shock towers sag and there are 1-piece export braces. I have always wanted to put strain gauges on the monte carlo bar and export brace just to see exactly what loads these members are subjected to. There will be some compressive force on the rear inner fenders, but again minimal compared to other forces. I wouldn't build a car without them though :p

    And to the guy that put in new frame from the tapered section forward. That really only provided a miminal effect on the rigidity of your frame (strictly speaking on what is visible in the pictures). From the suspension mount to the front of the car pretty much receives only dead loading from the body panels. If you have that tubing running from the end of the front frame rails to the rear frame rails then you should be good to go, assuming they start at the end of the tapered frame section. The tapered section now becomes the weaker link, depending on your tubing wall thickness. You did help reduce any torsion effects with the thicker front crossmember at the ends of the rails, but this would be taken care of with the crossmember for the MII suspension.

    I am not a suspension design engineer, so i don't have much to say about the design of the MII vs stock Mustang. I do know that there are numerous Mustang's out there on road races and tracks that are kicking some newer car's butts. They retained the same suspension geometry but have modified members (boxed upper and lower arms as well as other mods) to withstand the higher loads. In my OPINION, i think it is a crap shoot on which suspension handles better when comparing a MODIFIED classic suspension to the MII suspension. They both have their pro's and con's, but i agree with Reen that there is no structural worries ASSUMING you have the crossmember welded in correctly and with the correct electrode and fillet size. In laymen terms, no wire feed welder with a small weld :D Let me know if i can explain anything further, and hopefully i'm not overlooking something as i'm in a hurry to write this (end of the workday :D ).


    Edit: I just noticed that he does have the strengthened frame as subframe connectors. Curious as to why you didn't make your own tapered sections for tie the front frame and subframe connectors together?
    #90
  11. 68GT500KR_Vert

    68GT500KR_Vert Member

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    jbuening

    If you are talking about my car, the new frame rails go through the old ones back into the extensions into the TCP subframe conectors, rather then cut away the old back half of the frame rails we left them because they were in really good shape and that section of the car was strong. Anymore and we might as well have just built a complete frame.


    It's strong as hell anyway. My car is for the street and occasional strip/autocross.
    #91
  12. NasaGT

    NasaGT Founding Member

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    An excellent comment, this is what I have been thinking as I mulled over this as well.
    #92
  13. jbuening

    jbuening Member

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    Yeah sorry bout that, i didn't get the chance to read this entire thread at the time and just saw you pictures. Wasn't trying to point you out, just making an observation in case other's get ideas to replace their frame rails without anything between the front and rears.
    #93
  14. mrmustangman357

    mrmustangman357 Member

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    using strain gauges? I think there would be more movement than what a strain gauge would measure. I recall seeing XV motorsport's development testing on a mopar. They used two pieces of masking tape, attached in an X fashion across the entire engine bay. When subjected to normal street driving with bumps, one piece of tape would bend as much as an inch.

    Jbuening, I am a 3rd yr engineering student, working at a major aerospace manufacturer right now. Leaves plenty of time to work on projects
    #94
  15. jbuening

    jbuening Member

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    Did this Mopar have any engine bay bracing? I would be amazed if our panels deflected that much, because we would have fatigue problems at those little spot weld locations. Remember that the strain gauges only check for elongation or shrinking of the material and not bending/deflection. A foil strain gauge placed on the center of the monte carlo bar will measure how much the bar compresses and you can get the strain, which eventually will give you a rough estimate of the compressive force on the bar. Same goes with the export brace. Place one gauge on the expected compressive side and one gauge on the expected tensile side of the brace. Hopefully this makes some sense. I'm 4 years out of college (preparing for my SE exam), so it's been a little while since i've messed with these strain gauges. Sounds like you have your foot in the door at that place (i assume you are an intern there).
    #95
  16. mrmustangman357

    mrmustangman357 Member

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    It was on dream car garage on speed channel. It was a mopar B body I believe (70 barracuda). It was the stock config with no factory bracing, completely stock. Here was the setup:
    http://xvmotorsports.com/engineering/sus_proc_fourpost.cfm

    it doesn't show the tape thing. Not to get off the point, flex does occur in these vehicles. Remember raising the car up on a jack on the crossmember, then putting jackstands right underneath the torqboxes (installed on my coupe) then letting off the jack. You will notice the front end drops considerably after the car is bottomed on the stands, compared to the rear of the car rising on the new pivot. I realize now in this discussion that this moment force should be of much greater consideration than a possible twisting force on the frame rails (as viewed from the front - see earlier post). This isn't inclusive to the MII setup, but just a general location of flex for most all musclecars, camaros, mustangs, ramblers, IIs, chevelles, etc all didn't have triangulation in the front, contributing to this flex. Is it significant? probably not. But because this thread is attempting to deal with the loading effects of the MII setup, it may be worthwhile to also consider both the MII and original design's opportunities for improvement. The only triangulation the factory Mustang setup had was those stamped steel braces (which did little anyway) and the angle-bent sheetmetal the fender attaches to. After reading this thread, I now realize from some very smart people that the MII makes up for this slight bracing with the additional reinforcement to the frame rails. Will it work forever on a street car? probably. The only one available with triang. is the martz kit, which is marketed to drag racers that need absolutely zero chassis flex, and would run a down bar off their cage to that location anyway, regardless of whether an MII or original suspension was there
    #96
  17. jbuening

    jbuening Member

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    The majority of the flex is caused by the unibody system on these cars. In stock form, if you jack up the car under one tire the car will flex an inch or two and eventually the other tire will come off the ground. If you add sturdy subframe connectors, you can jack up under one side of the car and the other side will come up with it without that large deflection. Granted there will definitely be some deflection, but not as pronounced. My point was that there "should" not be a large deflection of the shock towers when you have the one piece export brace and monte carlo bar (which was where those strain gauges would go).

    Back on topic, i think even the stock mustang would benefit with something like the Boss 302 crossmember that had plates that tied into the lower control arm mounts to stiffen that area up.

    It appears that the MII suspension lowers the mounting points of the control arms based on the mounting location on the crossmember. I don't have the measurements between the mounting location of the upper arm and lower arm, but if the distance is less than the stock mustang suspension then there is less of a moment arm; therefore less torsion applied to the frame rail. This crossmember will take up most of the torsion applied to the frame rail (causing bending in the crossmember). The stock mustang suspension relies on the torsional rigidity of the frame rails, which is where the export brace and monte carlo bar help tie things together.
    #97
  18. 1320stang

    1320stang Founding Member

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    I guess what we need is for someone (who's planning a MII conversion) to volunteer to remove their front and rear side pans and leave the stock styled suspension in the car, keep the export brace and go to a track day somewhere and tell us how it performs.
    #98
  19. mustbereel

    mustbereel Member

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    That would be an interesting experiment. It would be fun to do it without the hood so you could see any movement.

    However, it has nothing to do with the MII conversion since the front and rear sidepans are retained.
    #99
  20. lauras70mach1

    lauras70mach1 Member

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    WTF :rlaugh:

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