IRS vs. live axle weight diff.

Discussion in 'SVT Tech Forum' started by EXTRPR50, Sep 10, 2006.


  1. EXTRPR50

    EXTRPR50 Founding Member

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    Has anyone done any research on if there is any weight savings going from a Cobra IRS to a live axle? I know there has to be some hardcore guys looking for every bit of weight savings. I was curious since I always read how heavy the 03-04's are.

    And is it cost efficient?

    95 GT, soon to be sold, 03-04 will replace.:nice:
    #1
  2. svtpower

    svtpower New Member

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    its

    A solid axle is 85 lbs lighter than the IRS.
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  3. Uncle Meat

    Uncle Meat Banned

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    I believe the weight savings is actually a lot more than 85lbs. It's closer to 150!

    There's some major benefits in swapping out the IRS for an 8.8 axle out of a GT. Disadvantage is you will lose a small amount of ride quality. Whether it's cost effective is another thing. Are you wanting this weight savings because you drag race the car, or because you want to cut through the twisties? Here is a detailed thread on performing the swap:


    http://www.svtperformance.com/forum...914 b6bda9a3eae1b4c6f722a82058&threadid=94768

    U.M.
    #3
  4. EXTRPR50

    EXTRPR50 Founding Member

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    Thanx, Meat.
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  5. svtpower

    svtpower New Member

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    strange.

    Thats very strange all the articles I have read say about 80-85lbs.

    "The Cobra IRS arrives already assembled and aligned at Ford's River Rouge Mustang factory in Dearborn, Michigan. Ford even uses the same machine to lift it into place that the solid-axle Mustangs use. The IRS assembly weighs about 80 pounds more than the solid-axle setup on the Mustang GT, but it allows a 125-lb reduction in unsprung suspension weight. To compensate for the heavier rear end, the engineers lightened the front end by 95 pounds, providing the 1999 Cobra with an improved 55/45 percent weight distribution, compared to last year's 57/43 percent."

    Taken from: http://www.thecarconnection.com/Veh...es/1999_Ford_SVT_Mustang_Cobra.S184.A763.html

    or

    http://www.edmunds.com/insideline/do/Drives/FullTests/articleId=44115

    U.M. knows his **** though, so this information may be incorrect, I am just not sure why there would be such a large discrepency.
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  6. Uncle Meat

    Uncle Meat Banned

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    I know of a few guys over on ModularFords.com who have actually weighed them side-by-side and are reporting the savings at 150lbs. Maybe the 03/04 IRS is heavier than previous years? :shrug:

    U.M.
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  7. bditty50

    bditty50 New Member

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    Hello I'm looking to swap my solid axle from my 1989 notchback to a cobra irs. I think its well worth it in handling even though I have all the maximum motorsport 3 link rear parts and torque arm. I want to step it up to an IRS for handling and put all the kenny brown tubular parts. These parts are said to have a 40% weight decrease on an IRS. Then if you go with the level 5 halfshafts they can handle 1000 hp. They have been able to handle cars in the 9's. The research in weight difference never seems to be sure I cant figure it out either I've asked everyone. I think the live axle so I heard weighs 150lbs so if the IRS weighs 150 more do the math. The IRS is more expensive in the parts department but, I think its totally worth it.
    #7
  8. Uncle Meat

    Uncle Meat Banned

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    Cobra's have only been coming with an IRS rear since 1999. Are you sure you can even adapt an IRS into your 89 without major modifications? Additionally, the level 5's are rated at 950RWHP. :D

    Picture of an 8.8 sitting next to a IRS from an '03 Cobra. I can see 150lb difference...

    [​IMG]

    U.M.
    #8
  9. Dope 97GT

    Dope 97GT New Member

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    what kind of power can the IRS hold well...thats why i thought most people swapped them out because they are not as strong and cheaper to upgrade?
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  10. Uncle Meat

    Uncle Meat Banned

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    Which IRS are you wanting to know about? The pre-03/04 Cobra IRS? A stock 03/04 IRS? A modified IRS?

    Most people swap them out because they are costly to upgrade for high HP cars. They are also heavy and of course prone to wheel hop. If a Cobra owner wants to drag race his car a lot then a straight axle is the way to go.

    U.M.
    #10
  11. Dope 97GT

    Dope 97GT New Member

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    well im planning on getting a 03/04 cobra in the spring and will prolly just do exhaust tune cai and pulley...so i was just wondering if the IRS in the 03/04s were reliable for around 450-500hp.
    #11
  12. Uncle Meat

    Uncle Meat Banned

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    Depends on how bad you let it wheel hop. :D

    If you plan on running it at the track occasionally you might want to think about an IRS brace so you don't bust up your differential cover.

    This part...
    [​IMG]


    Helps prevent this problem!
    [​IMG]

    Now there are guys who've been beating the snot out of their stock half-shafts with 500 or mor RWHP and never had a problem. There are also some poeple out there who have snapped the stock half-shafts with a stock Terminator on the street. :eek:

    U.M.
    #12
  13. 95 yellow 5 0

    95 yellow 5 0 Founding Member

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    mines not an 03/04 but the rear feels "solid" (pun!!) after the mods i did to it. i get the handling and ride of IRS with some added strength and dependability. unless you're constantly going to the track, there's no need to switch to solid. you won't even feel the weight difference anyway.
    #13
  14. bditty50

    bditty50 New Member

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    You can make an IRS weigh almost the same and not have any wheel hop with the right parts. The control freak kits weigh only 4 pounds more then a solid axle and have no wheel hop. Kenny Brown tubular parts do the same as well.
    #14
  15. Uncle Meat

    Uncle Meat Banned

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    Never heard of control freak kits before, got a link? As for the Kenny Brown stuff where you gonna buy it? Kenny Brown is temporarily out of business.

    U.M.
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  16. bditty50

    bditty50 New Member

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    Well I emailed Kenny Brown and they say they can still ship parts so I dont know whats the deal. I read the article in MM&FF and they installed a Control Freak IRS into a 2005 mustang. I contacted them to see if they had fox chasis stuff and they will produce it because of alot of requests. The problem is their kit is almost 10,000 because they do a low production of parts and they pay alot of attention even going to lengths of cryogenically freezing metal parts for strength. The only part that they have to swap to a stock IRS is their own differential. Their differential by itself is rated at 750+hp which is great and has more meat around the pinion where people normally have problems. It also has a forged aluminum cap. So I'm thinking about using their diff. for my swap and getting Kenny Brown tubular parts. This should make for a good setup. Another thing with IRS is to keep the diff. cool they get very hot.

    Control Freak http://www.bluemooncars.com/bmm-store-catg-cfs_tubulararms.htm
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  17. Uncle Meat

    Uncle Meat Banned

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    Unfortunately bditty50 your solution is probably not what he's looking for...

    U.M.
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  18. bditty50

    bditty50 New Member

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    I've read from various suspension technical guys that the extra 75lbs you get with the IRS over the Solid axle makes the weight transfer alot better in the mustang.
    #18
  19. Kilgore Trout

    Kilgore Trout Fried or Broiled ?

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    If you put a gun to my head and said; "You have to do the solid axle swap on your Cobra!" I would say; "Shoot me..."
    #19
  20. spyne

    spyne New Member

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    U.M., I don't think you are comparing apples to apples in this photo. The 8.8 in the pic shown doesn't have brakes, shocks or upper and lower control arms, all of which are on the IRS piece. That's not to say that the solid axle isn't lighter, it is, I just don't think this picture gives an accurate representation of the differences.
    #20

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