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Best rear for FF cobra

Discussion in 'Open Track Racing' started by 598, Apr 1, 2019.

  1. 598

    598 Well-Known Member Established Member

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    Car is only 2200 lbs. 600 hp. Is Thorsen still the best rear for a road course and street, and 28 or 31 spline?
     
  2. biminiLX

    biminiLX never stock Established Member

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    Torsen?
    What rear is in the FF Cobra?
    31-spline Torsens in the ‘13-14 GT500 SVTPPcars and ‘12-13 Laguna Seca Boss Cars are pretty affordable.
    -J
     
  3. railroad

    railroad Well-Known Member Established Member

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    The MkIV edition of the FF roadster uses the IRS carrier from the Mustang. The hubs and brakes are Mustang, but I think the axles are unique to the roadster. These cars are very twitchy and need something that does not lock and unlock abruptly. I think the traction lok with clutches and Torsen do OK in the roadster chassis. DSC03014.JPG DSC03013.JPG
     
  4. Norm Peterson

    Norm Peterson Member Established Member

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    Hmmm . . . sounds like lower bias might be a better choice than high bias.


    Norm
     
  5. 598

    598 Well-Known Member Established Member

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    Its an earlier car with a donor mustang 8.8, 28 spline. No IRS. Am trying to decide if adding the weight of 31 spline axles is necessary because the car is so light. Figuring a Torsen T2R right now, as that works great in my 95 R. but it is a heavier car and has less HP than the kit cobra
     
  6. biminiLX

    biminiLX never stock Established Member

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    I was thinking that too, with the light weight and power planned, I guess it depends how you’ll drive the car.
    If you ever plan to drag the car or launch it on drag radials, the 31s are probably a good bet.
    If it’s just spirited street driving and some road course fun, 28s should be good.
    600hp is a ton in a sub 2500# Cobra, so the rear will get some stress, but I’m guessing you’ll be Traction limited. What tires?
    I’m interested as I’m planning on a Cobra build for my wife sooner than later. She not one for power, so I’m thinking 5.2 Voodoo. Low torque under 4000; great for her. I’ll use the 4000-8250 range :)
    -J
     
  7. Norm Peterson

    Norm Peterson Member Established Member

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    Does the car have the OE Fox's triangulated 4-link rear suspension (aka quadrabind) or FF's later-option 3-link + PHB? The difference in geo roll center heights probably has some influence on the choice of bias ratio, which might not be available in both spline counts.


    Norm
     
  8. railroad

    railroad Well-Known Member Established Member

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    Most of the MkIV's end up tail heavy. The engine sits behind the front axle line. Even with the battery up front, the rear is heavier. I am sure even a stock push rod 302 feels strong. I am running the A50XS, not on the road yet, but about to make a trip out the driveway soon. For tires I am have BFG Rivals 1.5 S in 245/40/18 and 315/30/18s.
     
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  9. 598

    598 Well-Known Member Established Member

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    Has a 3 link + phb. 28 spline c clip. That's another question, should we switch to c clip eliminators. Tires are nitto NT 01s 275/40/17. If we go to the T2R, anyone have a favorite source for unit and axles. I've had great luck with Mosers thru out the years.
     
  10. AustinJ427

    AustinJ427 Well-Known Member Established Member Beer Money Bros.

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    While I don't have any experience with them, it's my understanding that you probably should go to a c clip eliminator if the car sees track time.

    With 600hp, even though the car is light, I would probably be more comfortable with a 31 spline.

    I'm also curious if you will end up going to a wider rear tire if you are currently 275 square. I've been on track with a few cobras and they are lively to say the least.
     
  11. 598

    598 Well-Known Member Established Member

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    Factory 5 said they use the standard ford unit, which was destroyed. We are going with a Yukon clutch type posi and aftermarket axles, with C clip. The C clip eliminator axles are really for drag racing from all I can find.
    Thanks for the input.
     

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