IRS swap here I come!

Prime Lord · Mar 10, 2013

Quick turn around on the SN classifieds netted me this from RdRunner:

I start disassembly of the existing rear next weekend.

Let the fun begin!

What this also means is that I'll have some North Cobra brackets, axle shafts, & MM LCAs for sale reasonably soon.

mob · Mar 10, 2013

I WANT!! how difficult is this swap?

madspeed · Mar 10, 2013

friend of mine recently bought an irs setup to put in his 240z. Think he paid $600 for everything

aar0s · Mar 10, 2013

I remember a while back there was an piece in one of the magazines about a fox with IRS out of (i think) a Thunderbird. If i remember right the guy had to make a couple of brackets but they made it sound like it was damn near bolt in. This is a swap I always thought would be cool, good luck!

Prime Lord · Mar 11, 2013

Yeah, the Cobra IRS rear is essentially bolt in. Just have to drill some holes in the frame rails for the rear side brackets. Plus I need to source brake lines and replace some of the rubber with poly.

84Ttop · Mar 11, 2013

Awesome swap, we have a few cars running around South Jersey swapped to IRS and they handle incredibly well. Good luck!

89gtstalker · Mar 11, 2013

I put an IRS in my car. It is not too difficult. You have to drill from the lower frame rail into the trunk area for the top mounts, and either drill and sleave, or modify the third shock mount. The cobra frame rails have two holes straight across from each other, and the fox third shock mount is offset, so the side bracket holes only line up in one spot.
For the bottom two rear mount holes into the trunk space, I had two plates made(3/8" steel), about 3"x6" with holes to match the lower frame rail mount, that sit in the trunk and span the frame rails, for added support. I also sleaved the frame rail between the plate in the trunk and inside the frame rail. You can read some information here.

http://www.mouthbreather.net/IRSSWAP.HTML

RacEoHolic330 · Mar 11, 2013

Reinforcing the frame rail is probably the most important part of the swap. Without some kind of sleeve or tubular reinforcement, you'll damage the frame rail by collapsing it.

It also really helps if you strip the subframe down. The IRS is a real bitch to mock up when it's all together. If you can swing it, I suggest using delrin for as may bushings as possible. It's not cheap or easy to install the delrin bushings, but it definitely makes a difference as far as wheel hop is concerned.

I think my favorite part about the IRS is the look of the tailpipes behind the car. So sexy.

Mustang5L5 · Mar 11, 2013

Nice!!

I remember passing up an IRS a few years back because I had noplace to store it. Guy wanted $600 for it. I still kick myself.

One day....

Prime Lord · Mar 11, 2013

I was looking on the Maximum Motorsports website and they have a bushing/bolt set that is appropriately sized to bolt the IRS up to the fox chassis. I don't plan on ever drag racing it so I'm not too bent out of shape about wheel hop. Poly bushings and braces are all I'm really concerned with. I'm also going to get the stainless brake lines. It has no brake lines at all right now. I just need to source the correct T fitting for the hard brake line.

Mike,

I couldn't pass on the deal. Got it for $750 and since I already have the vented cobra brakes out back and I only put those on 6 months ago, that stuff is a direct swap with no additional cost.

Scott,

Stripping down the module is something I hadn't really considered. But I can see how that would make it a LOT easier. Does it make more sense to sleeve and reinforce the frame horn or just weld the bracket up and not drill any holes?

Mustang5L5 · Mar 11, 2013

you can prob recoop some cost from the sale of parts you remove. Axle, exhaust, misc hardware, etc.

I'd be doing a happy dance right now if i had one of those laying around. It does add a little weight, but it adds it in the right spot. Take off a little weight from the nose and you are getting pretty damn close to 50/50 weight distribution and losing that annoying axle skip in a hard turn

RacEoHolic330 · Mar 11, 2013

Prime Lord said:
Scott,

Stripping down the module is something I hadn't really considered. But I can see how that would make it a LOT easier. Does it make more sense to sleeve and reinforce the frame horn or just weld the bracket up and not drill any holes?

Here's what I did. Starts about 1/4 down the page.

http://www.stangnet.com/mustang-for...n-thread-dart-331-turbo-irs-etc.848816/page-5

Welding the bracket is probably an option, but it makes things very permanent. It would also eliminate the 'wiggle room' that you have when removing and installing the subframe. Being able to have the bracket loosely in place while you're manuvering the subframe into position really makes the install easier. I would also suggest using a threaded rod, nuts, and washers to open up the lower torque boxes on the car. Greasing up the lower subframe mounts on the IRS also helps. It's a very tight fit.

What wheels are you going with? The 3" wider track really narrows the available wheel selection. Rolling the fenders is pretty much mandatory with the IRS.

Prime Lord · Mar 11, 2013

Right now I've got the American muscle clones of the 2012 GT500 wheels. They are 18x9 w/ a +30mm offset. I'm hoping I can go to a pair of legit GT500 wheels in the rear which are 18x9.5 and have a +45mm offset. I just bought the wheels less than a year ago along with brand new 245/275 shoes and I really don't want to change all 4 again. The tires probably have 100 miles on them. Plus I love the way they look.

RacEoHolic330 · Mar 11, 2013

Any S197 wheel should be a good fit, especially with 45mm of BS. The 94-04 wheels are not as backspacing friendly as the 05+ ones. I think you'll be fine.

stykthyn · Mar 11, 2013

I was always worried about finding wheels that fit. s197 wheels are a good match? I would love to keep my fr500s and if an s197 offset will work that would be tits.

RacEoHolic330 · Mar 11, 2013

A 45mm offset wheel will definitely fit nicely. 45mm is the stock offset for the S197 wheels (possibly all of them, but don't quote me). My '01 Cobra wheels are 30mm offset, so they will stick out a tiny bit more, but luckily there is camber adjustment with the IRS, so the wheels can be tucked to offset the offset .

I don't think a 9.5" wheel with 30mm offset will fit without rubbing the subframe mount. 45mm should do it though. I would say the main downside to the IRS is that tire sizes over 275 are just about impossible without major modifications to the subframe or fender flaring

Prime Lord · Mar 11, 2013

I'm good w/ keeping the 275s that I have now. Its just a question if going from a 9" rim w/ +30mm offset to a 9.5" rim w/ +45mm offset will make enough of a difference.

Good point on the camber:

But srsly, if I have to take in a few degrees of negative to make them fit, I'm good with it.

I just had a chance to read through your description/pictures in reference to the plates and tubes on the frame rail. I need to be able to buy these. hehe. I completely understand what you did there, but I also completely lack the ability/tools to fab them myself. Do you have the dimensions on the bolts that you put in? Are they the same specs as the factory bolts? because I have all of those.

IRS swap here I come!

Prime Lord

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mob

the guy who hits on his mom

madspeed

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aar0s

Prime Lord

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84Ttop

They make new pistons every day, so why worry?

89gtstalker

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RacEoHolic330

I like to dress like a pretty girl

Mustang5L5

That is…until I whipped out my Bissell

Prime Lord

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Mustang5L5

That is…until I whipped out my Bissell

RacEoHolic330

I like to dress like a pretty girl

Prime Lord

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RacEoHolic330

I like to dress like a pretty girl

stykthyn

I want to measure mine. It doesn't look that tall.

RacEoHolic330

I like to dress like a pretty girl

Prime Lord

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