FIRST LOOK at the S550 IRS !!

Discussion in '2015+ S550 Mustang 5.0L Tech' started by [email protected], Sep 5, 2014.

  1. BMR Tech

    BMR Tech Traction Vendor

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    The S550 IRS Subframe alone/bare bones, weighs 55lbs. Just thought I would share that. ;)

    As for the IRS in general, our 2010 Camaro has cut MANY low 1.3, high 1.2 sixties. We did recently break a halfshaft. We discovered it was one of the early GForce units....and was not rated much above 800HP. We have been making 900+ftlbs for 3 years. lol!!! Rest assured, we now have the Outlaw Shafts from Gforce.

    On that note, I do have some GForce/FRPP Halfshafts on the way for my 15. I was more than excited when GForce told me they were building their baddest of bad halfshafts for the FRPP pieces. Those shafts are withstanding 1500HP, and have never seen a failure. That is astounding.
     
  2. RED09GT

    RED09GT Senior Member

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    That time frame does change things but really since the late 80's most rear wheel drive "performance" cars have been IRS, it really is only the mustang, camaro, and trans am (or firebird, whatever) that were the holdouts to this. RX7's, BMW 3 series, corvettes, 300ZX's, supras, even 89 and up t-bird SC's had independent rears.

    I can't comment on the 60's and 70's but the automobile has come a long way since then chassis-wise in general.
     
  3. BMR Tech

    BMR Tech Traction Vendor

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    Some other things to note:

    The bearings in this piece are very nice. Sealed spherical bearings all over the place.

    The forward mount support plates are pathetic. Rest assured, we are already developing some new ones....that are thicker, with tighter than Ford tolerances. These plates should help drastically with subframe fore/aft shifting...and will be great for those not looking for much NVH increase. Of course, they will be very good for those looking for maximized IRS rigidity too.

    Camber - haven't seen a way to adjust it. We are already looking into making an adjustable relocated upper arm. It is very complex, though.

    Toe - the toe rods are actually pretty damn good. We have already built some prototypes though, that are very strong...and lighter. Yes, it is possible! They also allow for more adjustment. The OEM design features an eccentric bolt...but I prefer using a solid mount over the eccentric with a truly adjustable arm/rod, personally. On the other IRS Platforms we support, we have seen too much inconsistency with eccentrics when really being put to use.

    [​IMG]

    The spindles, lower arms, etc (all the aluminum) are very nice. Engineered nicely, and unfortunately....there won't be any reason for the aftermarket to make these pieces (other than what I mention below about wheels)

    The brakes, are great. The clearance is VERY good...as the outer portion of the calipers only protrude from the mating surface of the rotor by 5/8" - someone was thinking about the drag racers when making these, kinda.

    The combination of the larger rear brakes, the spindles, and the RLCA make it impossible to run a wheel smaller than 17" for the drag racers. It is not like the old days, when I could spend 6 hours in my shop finely grinding away here and there, to get my 15" wheels to fit my '04 Cobra IRS and Brakes...

    There is a REALLY good chance that we will be offering a 15" wheel conversion kit, like we do for the 2010+ Camaros. The question is, will the Ford market accept and pay $4000 for it, like the GM market? LOL

    Shocks and springs.....the shocks seem to have a ton of compression stiffness. The springs seem to be very stiff as well. Makes sense. I hope to have some spring data (rates) as well as shock dynos very soon to share. We always get this data for engineering our BMR brand components, as every company should. And of course, I will definitely share anything I find out. For example, the front Sway Bar on the 2015 GT is 433lb/in. Even though it is substantially smaller in diameter than the 11-14 cars, it is only 3lb/in away from the 11+ 436lb/in..

    The shock and spring design could be better in my opinion, in terms of placement / and aftermarket. As in, it is going to be much more difficult offering a coilover kit for this car, from what I can see. If you place a C/O kit where the shock is, you will have Wheel/Tire clearance issues....and if you run it where the spring is, well, you will only have a 5" tall C/O Kit. ha!

    Fingers are tired. Wife bought this new keyboard and it feels like pressing down on a solid floor.
     
  4. Norm Peterson

    Norm Peterson corner barstool sitter

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    I've seen the video . . . and I have to wonder if your crew had some reason to expect it to break just in time to record it happening. Some have commented that the shaft didn't appear to be running true in the burnout box just before it died at the line.


    I guess you could call the Mustangs and F-bodies "holdouts", although that's more because whether you look at the original muscle cars for being RWD or for their performance the last of them went MIA when the RWD Monte Carlos and the turbo Buicks went out of production. I'm not getting the feeling that the current crop of "performance sedans" (G8, GTO, Charger, SS) is quite there yet, either, so the kind of rear suspension they're using is still a rather moot point.


    Norm
     
    Last edited: Nov 12, 2014
  5. FL BILL

    FL BILL Junior Member

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    Irs rear ends

    I never liked the way my C5 Corvette handled accelerating out of turns when the traction control was turned off. It could get out of shape in a hurry. I wonder how the '15s handle coming out of a turn under full throttle?
     
  6. DRock

    DRock Senior Member

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    so....where are the swap parts? Anyone?
     
  7. warmmilk

    warmmilk Junior Member

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    can someone explain how the whole vertical link thing works? it seams to me like it just adds weight and complexity... I don't see how the suspension would move any differently if the vertical link wasn't there and the lower control arm just connected to the hub at the bottom
     
  8. Norm Peterson

    Norm Peterson corner barstool sitter

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    Without it, the suspension would not be a stable mechanism. The UCA (perhaps aka "camber link") cannot positively locate the upper end of the hub carrier because it has only a single pivot at each of its ends. Think fore/aft direction as seen in side view for the kind of movement that it cannot control.

    The integral link does resist that kind of motion by tying the upper end of the hub carrier back to the LCA so that the hub carrier cannot rotate (at least not uncontrollably) about its lower end connection point [to the LCA].


    Norm
     
    Last edited: Jul 16, 2015
  9. warmmilk

    warmmilk Junior Member

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    fore/aft as in inside of the car to outside of the car? side to side if looking at the car from the front or behind? I'm assuming this is what you're talking about as the bushings aren't arranged correctly for front to back motion...

    there are plenty of other cars (well I can think of only one right now actually, S2000) with a single upper arm... isn't that standard double wishbone setup for rwd? upper arm, lower arm, and a toe arm somewhere in the mix?
     
  10. Norm Peterson

    Norm Peterson corner barstool sitter

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    Side view

    [​IMG]

    In the case of the S550, without the IL, the independently sprung rear wheel would only be held against forward/rearward displacement by the LCA. That leaves freedom for the wheel to flop back and forth about the hub carrier to LCA pivot.

    Mathematically, an independent suspension needs to provide geometric wheel control in exactly 5 of the 6 degrees of freedom. So when you see an IRS described as a "5-link", it's exactly correct and proper. Not just an attempt to impress by using as big a number as possible.

    In a S550 with its IL removed, only four DOFs would be under control (by the UCA, LCA, and toe link either individually or in combination with each other).

    If you swapped the IL for a UCA with two pivots on the chassis side, you'd have a "conventional" SLA arrangement that's easier to understand. So maybe think of the IL as being an unusual substitution for the second chassis side pivot?


    Norm
     
  11. warmmilk

    warmmilk Junior Member

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    oh ok, that making some sense now..

    so whats the advantage of using an IL over a more conventional setup?
     
  12. Norm Peterson

    Norm Peterson corner barstool sitter

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    Space requirements - not just fitting it in statically but avoiding everything else in the vicinity over the entire range of suspension travel. Everything out near the hub carrier is connected to it and more or less moves along with it. So whatever static clearance you have tends to not change much. Unlike, say, a frame member/subframe/exhaust pipe/spare tire well/etc. that you'd have to make a "real UCA" stay clear of.

    I think it can be used to tweak the anti-squat % a bit (working in conjunction with the LCA's chassis-side pivot locations, and it appears to allow a more comfortable compromise between anti-squat and rearward wheel compliance going over bumps (slight rearward travel takes out some of the "sting").


    Norm
     
  13. warmmilk

    warmmilk Junior Member

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    thanks for the education :D
     

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