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post #1 of 15 Old 08-21-2011, 04:04 PM Thread Starter
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More fox IRS Q's....

I'm collecting parts for a Fox IRS swap and I had som questions that I did'nt see covered by the many many pages of info on the search. Great stuff by the way!!

I have some H&R black springs. Are these the springs I want for my fox swap or do I want the steeda 850/1050 springs I have now, and get new pair of rears?

Also I have some koni yellow sa's on the car now, do I want to run the factory 03 Bilstiens, or buy some koni's for the IRS to match my adjustable fronts?

Can I use the front spindles from the 03, or do I need to run the 94/95 spindles?

I got the hydro boost from the car too. Can I run this set-up with instead of the deal I have on my coupe with the 95 booster/v-6 m/c/ willwood prop valve?

Any help is appreciated.


Starting soon: 98 PI Swap/3650, IRS, ABS 6-piston Brembo, (possibly 4-eyed) 92 coupe.
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post #2 of 15 Old 08-21-2011, 06:19 PM
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You will need the 94-5 ft spindles on the front. I think the IRS requires a different shock than the solid axle cars. I have a set of 94-95 spindles that I would work out some kind of a trade for the Konis if you go with the Bilsteins.

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post #3 of 15 Old 08-21-2011, 08:23 PM Thread Starter
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I know the rears are different. I was more wondering if the konis would be better for autocross than the bilstiens. Also if the valving in the fox konis would be match the cobra koni rears. I figure I can sell the bilstiens to help buy the correct rear shocks.

Starting soon: 98 PI Swap/3650, IRS, ABS 6-piston Brembo, (possibly 4-eyed) 92 coupe.
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post #4 of 15 Old 08-21-2011, 09:49 PM
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id stick with bilsteins

u know that the IRS is weaker and heavier than the 8.8 right

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post #5 of 15 Old 08-21-2011, 10:50 PM Thread Starter
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Its out of a an 03 which stock is 400hp, and I'm going to be running a 300hp 302 so i dont think strength is an issue. As for the extra weight, I'm told it's 80lbs heavier. A tourque arm and panhard bar is going to add at least 50lbs.

Starting soon: 98 PI Swap/3650, IRS, ABS 6-piston Brembo, (possibly 4-eyed) 92 coupe.
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post #6 of 15 Old 08-22-2011, 12:10 AM
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A tourque arm and panhard bar is going to add at least 50lbs.
I find it funny that when the debate of SRA vs IRS comes up nobody ever mentions a word about those two components adding weight. I think most forget that adding a quality set of LCA's like a set from MM will actually add a few lbs. When I started kicking the idea around of swapping in an IRS everyone I talked to was real quick to point out the weight issue. After doing the swap finally I look back and wonder why I didnt do it years ago.
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post #7 of 15 Old 08-22-2011, 02:51 PM
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Originally Posted by darkside03gt View Post
I find it funny that when the debate of SRA vs IRS comes up nobody ever mentions a word about those two components adding weight. I think most forget that adding a quality set of LCA's like a set from MM will actually add a few lbs. When I started kicking the idea around of swapping in an IRS everyone I talked to was real quick to point out the weight issue. After doing the swap finally I look back and wonder why I didnt do it years ago.
When I measured the weight of my IRS and the weight of my old 8.8, it was approximately 100lbs heavier. I did this with a bathroom scale, but it seems like an accurate approximation. The biggest thing is even though it adds weight, there's less of it flopping around on the pavement. I don't regret my IRS swap for a second. I'll be removing it from my fox and swapping an 8.8 back in just so I can sell it (the car). The IRS is getting a bushing upgrade then being dropped in my new 94 GT shell

IMO, I'd buy a set of SA konis for the whole car. That way, you can fine tune if you need to. There are times I wish I could get my car to ride a tad bit softer on the street. A friend has SA konis on his Taurus, and it's amazing how he can go to an autocross, turn them up a few notches, run the day, then turn them back down to cruise home in comfort.

FWIW, I haven't had a bit of problem out of the strength of the IRS. It'll wheelhop on certain surfaces (tires affect it a lot too) but if you're already rolling, you're golden. Granted, I'm on stock 93 302 power, but as long as you aren't doing drag strip launches every friday/saturday night, you'll be fine.

Also, I suggest getting a larger front swaybar for your car if you install the IRS. My car was stupidly prone to snap oversteer without it. I installed an eibach front bar after I spun the car on the dragon and at an autox (that was messy). The car became immensely more balanced with a bigger front bar. Higher springrates in the front would do the same thing if you don't feel like swapping bars, but you didn't mention anything about that, so I'm assuming you've got a stock front end.

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post #8 of 15 Old 08-22-2011, 04:14 PM
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A tourque arm and panhard bar is going to add at least 50lbs.

No. With the MM TA / PHB, you remove the pinion snubber, vibration dampener, both upper control arms, both quad shocks and hardware, all of which is ~ 25 lbs.

When all is said and done, the net weight gain is only about 25-30 lbs. Less if you go with coilovers.

The other thing to realize if you are swapping an IRS into a Fox, you cannot run in C Prepared class, which is basically the American Iron equivalent (modified Mustangs and Camaros) for SCCA Solo. Nor can you run in ESP. Which basically leaves you with SM where you'll be competing with modified (and over-boosted) 240's, STI's, Evo's, BMW's, and other imports where it is highly unlikely an IRS Fox will be competitive unless you have a huge trust fund and Tiger Woods level talent (pre-scandal) at driving. But of course, you will still have fun with it, so if that is your only intent, then go for it. This is the biggest reason I put the brakes on the IRS swap. I still have an '04 Cobra IRS sitting in my garage wondering what the hell to do with it. Ebay, anyone?

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post #9 of 15 Old 08-22-2011, 07:12 PM Thread Starter
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I will be pillaging my 92 coupe, my wrecked 90 vert, and the 80 fairmont I just scrapped for the IRS.

My list of parts for the keeping will be the
Koni SA fronts
steeda front sway bar, (which is the thickest I've ever seen!)
fox front LCA's with offset bushings and X2's, r
ear IRS
cobra front brakes, possibly 00' "R" brembos if they'll fit my 01GT wheels
Steeda bumpsteer kit
Steeda CC plates
Strut brace

Unsure what springs, I have "C" springs, steeda comp springs, and the H&R sports that are for the cobra.

The last time I ran my coupe, they had me in the wrong class, and they ran me with STI's running slick's. It was still fun, but it always sucks when you times are 4 seconds slower than most cars in your class.

Starting soon: 98 PI Swap/3650, IRS, ABS 6-piston Brembo, (possibly 4-eyed) 92 coupe.
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post #10 of 15 Old 08-22-2011, 07:43 PM
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I put an IRS in my 93. I think it is just awesome. I did the full tilt boogie racing bushing upgrade and MM bilstein coilovers with a 525# spring rate. It is well worth it but I dont road race the car.


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post #11 of 15 Old 09-21-2011, 11:08 AM
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85 svo+04 irs=amazing improvement overall! will do irs swap on any stang i ever own... our 600 swb benz, 635 bmw, 65 shelby, svo, xj6 jag, even our lil bitty bmw 600; ALL irs, fk straight axles! lol

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post #12 of 15 Old 09-21-2011, 09:25 PM
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I've never really seen the point in IRS swap in solid axle car. It's more expensive, harder to setup, and the performance gains over a torque arm rear are hard to quantify. From what I've properly setup, one works just as well as the other on the track. The way I see it, just modify what your car came with, and call it a day. If I really wanted a comfort, I would not swap IRS over. I would sell the car and get a BMW.

94 Mustang GT. Stock.
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post #13 of 15 Old 10-21-2011, 11:29 PM Thread Starter
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Originally Posted by ReplicaR View Post
I've never really seen the point in IRS swap in solid axle car. It's more expensive, harder to setup, and the performance gains over a torque arm rear are hard to quantify. From what I've properly setup, one works just as well as the other on the track. The way I see it, just modify what your car came with, and call it a day. If I really wanted a comfort, I would not swap IRS over. I would sell the car and get a BMW.

I parted out a fairmont that had the IRS on it. By the time I scrapped thd chassis and sold parts, I ended up with a complete rotor to rotor IRS, cobra front brakes, spindles, rack, booster, bilsteins, h&r sports,
Bump steer kit, and alum diff bush's. All for $850. That's my complete susp and brakes for my four eyed coupe for $850 which wouldn't buy a TA set-up, let alone all the other parts.

That's my reasoning!

Starting soon: 98 PI Swap/3650, IRS, ABS 6-piston Brembo, (possibly 4-eyed) 92 coupe.
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post #14 of 15 Old 10-21-2011, 11:54 PM Thread Starter
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Oh yeah, and the 2.5" IRS exhaust with 2-chambers.

Starting soon: 98 PI Swap/3650, IRS, ABS 6-piston Brembo, (possibly 4-eyed) 92 coupe.
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post #15 of 15 Old 10-22-2011, 03:20 PM
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If you have time to spend, then I'm sure there are ways that you can have IRS in the car cheaper than buying a brand new torque arm. Don't forget that IRS will require a certain amount of modifications as well. I doubt that it will have the traction of torque arm setup right out of the box.

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