im getting a complete irs out of a 99-01 cobra for $400 with 373s and ebaich springs. but i want to know how strong this is? its stock 28 spline. what kind of hp levels will this take with some mickey et street tires? and ya some clutch dumping? how fast have you gone on urs?
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1990 5.0 Mustang LX, SBF 357 (.030), Speed Pro Hyper Pistons (for now, 427 later ), Camshaft? well its changed again, Nicely Ported Pro Comp 210cc Heads, Edlebrock Super Victor Intake, Barry Grant 850 Demon Carb, MAC 1 3/4 Long Tubes, TKO 500, Spec Stage 3 Clutch, 3 row radiater , Black Magic Elec. Fan, 6 point roll cage , Custom throught floor sub-frame connectors, 5 lug conversion, Rear disk brake conversion, and some Mickey Thompson ET Streests. AKA YOUR BASIC DAILY DRIVER
I own a 2001 Cobra Convertible with the IRS, it has been modified with the Vortech and dyno readings of 479 HP 456 Torgue, the only issue I have is wheel hop, terrible on dead end take offs. Fixing to put in Poly bushings that will eliminate the hop(Brothers Performance). Hope this helps, IF I had a choice, I would have gotten the live axle instead of IRS.
P.S. make certain your differential gasket is good before installing, Ford wants $700.00 to replace one, they have to drop the fuel tank and remove the rearend to change it, when in doubt, replace; while it is out of the vehicle.
The 01's had 31 spline haft shafts, so if your is 28 Spline it's a '99 IRS. A buddy of mine has a '99 thats been pushing 500 RWHP for over 2 years now and just bumped up to 550 RWHP and JUST broke his first haftshaft.
Wheelhop is basicly eliminated with a set of DR's.
Yup normally aspirated 99-01's have 28 spline, 31's started in 03.
And Ford definitely had handling in mind with the introduction of the IRS, they weren't developed for 5000 RPM launches on Slicks, so there's always a risk of breaking an Axle Shaft. I've yet to do a wheelstand burnout in mine, why chance it, haha!!
I read somewhere that they didn't put the 31 splines in till the 03 model.
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Yup normally aspirated 99-01's have 28 spline, 31's started in 03.
And Ford definitely had handling in mind with the introduction of the IRS, they weren't developed for 5000 RPM launches on Slicks, so there's always a risk of breaking an Axle Shaft. I've yet to do a wheelstand burnout in mine, why chance it, haha!
Nope sorry 2001 was the year
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While the 2001 Cobra shares almost all the same components of the 1999, some changes were made. The changes included:
The engine block was changed from the Teksid block to the Windsor Aluminum Plant or WAP block. The WAP block is regarded to be weaker than the previous Teksid block. Some 2001s received the Teksid, either from the factory or as a replacement motor
Newer revision cylinder heads.
Cobra-specific seats with a combination of leather and alcantara [suede-like microfiber] inserts - 1999 Cobras had normal Mustang seats.
A rear bumper that reads "COBRA", instead of "MUSTANG", as the 1999 Cobra had.
A rear badge on the trunklid was changed to say "SVT" instead of "SVT Cobra" as the 1999 Cobra had.
The wheels for the 1999 and 2001 are 17x8. The '99 & '01 were sold with silver powdercoated aluminum wheels. The 2001 had the option of polished wheels in the same style.
The T-45 transmission in the 1999 model was replaced by the 3650 in the 2001 model.
The IRS halfshafts and differential were changed from 28 splines in 1999 to 31 splines in 2001.
The spoiler was redesigned.
The CD player was upgraded to a 6 disc unit.
The center console and trim were redesigned.
The emergency brake was fitted with a 'boot' of leather to cover the hole in the console where it protrudes.
The headlights were changed from a chrome background to a black background. The newer headlights are sometimes referred a "smoked" or "tinted" but this only refers to the black background. The actual lenses are clear and identical to that of the 1999.
The color of the odometer digits was slightly changed, and the color of the instrument cluster lighting was slightly changed as well.
Here's a few threads that also covers the differences.
How strong is a stock 99-01 irs? 
), Camshaft? well its changed again, Nicely Ported Pro Comp 210cc Heads, Edlebrock Super Victor Intake, Barry Grant 850 Demon Carb, MAC 1 3/4 Long Tubes, TKO 500, Spec Stage 3 Clutch, 3 row radiater , Black Magic Elec. Fan, 6 point roll cage , Custom throught floor sub-frame connectors, 5 lug conversion, Rear disk brake conversion, and some Mickey Thompson ET Streests. AKA YOUR BASIC DAILY DRIVER
2001 was the year 
