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Discussion Starter #1
I will soon be running my 00 GT with an 01 IRS at the local SCCA gatherings, and I was curious about the IRS. Any special needs? Any "free" tricks for improvements? Any way to get some negative camber out of it? Anything to watch for? I will also soon add some 03 springs and Bilsteins.

For those of you running the IRS in Auto-X, what are your impressions?

Thanks in advance!
 

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I put an 03 IRS in my 97 Cobra and love it. I don't auto-x it but I open track it. Here is what I have done with it. MM urethane IRS bushings and a-arm bushings (upper and lower), Aluminum front diff bushings, delrin rear diff bushing, MJ's/Billet Flow's diff brace, 4.30 gears, bilsteins with MM coil overs at all 4 corners, 03 Cobra drive shaft. There isn't enough adjustment to get the amount of negative camber I would like for the track. I am thinking about custom a-arms with rod ends for that reason. I still want to ugrade to DSS level 5 half shafts.

As it is it works real well. By all means do the bushing while you have ithe IRS out already. They are a major pain in the butt to install.
 

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Discussion Starter #3
Did the bushings provide a noticeble difference? I've read posts comparing the improvements to adding a panhard bar to a live axle.

When lowering, any thing to watch out for?
 

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I did all of my mods to the IRS before I installed it so I can't compare it to the stock IRS setup. I can tell you that mine corners really flat and on the road it rides better than it did with the stick rear.
 

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coleman2kgt said:
Any way to get some negative camber out of it? Anything to watch for?
With the stock arms you can dial-in about 1.5degrees of negative camber. It varies from car to car. I would recommend negative camber even if you don't open track or autocross the car. You tires will thank you. The factory settings do a number on the outside edges of the rear tires.
 

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Discussion Starter #7
Thanks for all the great advice! What else? What about running sticky tires, any breakage issues?
 

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I have been unable to get anything near 1 degree negative with the stock a-arms. In fact it only gives me slightly less than .5 degrees. I'd love to be able to dial in -1.5.
 

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I haven't heard of any breakage issues in road racing or auto-x, only hard drag launches. If you want to be extra safe DSS level 2 half shafts should be plenty strong for all but serious drag racing.
 

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DSS is The Drive Shaft Shop. They make 2 different setups for our IRS. The level 5 stuff is indestructible. There are folks doing full drag launches on slicks with 700hp+ cars and I haven't heard of any breaking. The level 2's are plenty for a road racer though.

http://www.driveshaftshop.com/MUSTANGC.V..ivnu
 

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Discussion Starter #13
Well, sad to say, I have a stock SOHC for the time being. But that will change with time. Thanks for the link. So the shafts are the weak link in the IRS? I remember reading something about the knuckles breaking. Don't remember the senarios.
 

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The shafts are the first weak link then the outer cv's. The level 2's address the shafts and the level 5's include redesigned beefier outer cv's. The Level 5's are just awesome but probably not necessary for road racing. I still run the stock shafts in my 03 IRS. Everything else has been redone. If I break the stockers then I'll upgrade them. To date I've never had my Cobra on the drag strip, a road course is much more fun.
 

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Discussion Starter #16
Nothing better than nailing an apex!

Slightly off subject, but any of you guys had any luck dialing out the vibrations if the typical mustang IRS?
 

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Veeerrrryyy careful alignment of the driveshaft and pinion angle plus clocking the driveshaft. That should get you almost vibration free. A carbon fiber driveshaft will take the last little bit out. I tried a heavier driveshaft and it made things worse. You really have to play with it and can't rely on factory specs. especially if you change gears like I did. Going with 4.30's you just forget the dogbone.
 

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I'd be interested to know that as well or anybody running the KB modified subframe.
 
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