IRS on an '03 GT
 

Hi All,

I am new to these forums as of this morning, but found it while trying to figure out the answer to a question regarding my stang. I have a 2003 GT with no current suspension mods. (Stock springs, shocks, etc.) I bought the car to autocross, and have found it reasonable so far. However, I'm wondering dollar-to-dollar if I would be better off;

A) Lowering the car with a spring/shock change and stiffening it with a Panhard bar and stronger front sway bar

or

B) Trying to find an aftermarket IRS kit. (I thought at one point I found a link to the Bentler IRS units they made OEM on the Cobra's but can't find it anymore.)

Is the IRS change even do-able? Is the IRS worth the thousands it would cost to buy and install? Or am I just better off sticking with simpler mods, tires, and some engine tricks?

I tried searching for this using both the search and by clicking around and couldn't find an answer. Sorry if this is a duplicate post.

Yes it's completely do-able. If you really wanted to go with IRS, you could search around and probably find someone with a 03/04 cobra that wants to trade for a solid axle. I've seen people trade IRS for solid axle plus a little cash. From what I hear it's a pretty simple swap. Wait until R3DN3CK chimes in cause he's gone through a few suspension setups including IRS and solid axle.

Kewl...
 

I heard that the design of the IRS system was such that the parts were built for quick changeovers to the Cobra IRS at the factory, and that could they be swapped, but I never thought of trading with someone... (DuH me...) I would have been back here 2 weeks later selling a solid axle... :-P

I had a stang back in the 80's when I was young and foolish... Now that I'm old and foolish I decided I needed a toy... ;-)

The IRS would be a great option for the rear of the car. I would like to do the same as I Autocross often. Just an IRS would not be the end of your suspension modification needs though. In option A you have plans for the front and rear, option B just being the rear. You will need a blend of both. A good plan would be to do the IRS swap with rear coilover with the proper spring and dampening rates, and coilovers in the front with the proper spring and dampening rates also, using sway bars as a tuning tool. A 3-link SRA would also be a good option with the correct spring and dampening rates, and keeping your steering geometries correct. I will probably end up going with a PHB/Tq. Arm SRA setup unless I come across an IRS.

I say go for the IRS if you can get your hands on one and have the money, but have a plan for the rest of the suspension also. If you go with the more common spring/dampener change, make sure you really help the handling characteristics of your car. If you lower it too much you will make everything worse. And don't forgets about a Watts link.

I'd recommend you not bother with the IRS.

MM Torque arm and panhard bar is a much more durable setup that handles better than the IRS and isn't nearly as expensive to do. I broke my IRS so many times it's not even funny. I poured money into parts and broke it some more. If you beat on them they break, period. Stick axles are way more durable. This weakess is not native to all IRS's but it is native to the SVT IRS found on 99-04 cobras. It was an afterthought and it shows in the design and performance. It's better stock for stock than a solid axle by a long way but it's way behind when you get to serious suspension modification for serious performance.

If you want to eliminate the left/right turn difference from the PHB, look into a watts link. REALLY consider the noise you're willing to live with before you do a watts though.

For a good starting point, I'd go with a MM 4-wheel coil over set with 350-375# front springs and appropriate rears for whatever rear setup you end up with. To start in the rear, you could easily drop in a set of MM RLCA's, and PHB then turn to the front with MM tubular a-arms, upgrade to a better set of sway bars and rock it. You can upgrade to a tq arm later if you want. The difference with just those parts will be light years from what you have now. I drove that combo for almost a year and it rocked. I wanted more grip in the rear to hold the 5.4 down so I put the tq arm in too. That BTW was a good decision on my part.

BTW... I can swap an IRS in in about 4 hours. It's retardedly easy to do. If you decide to go that way and need a set of rear upper cradle brackets, I have a set spare in the garage you can have for cheap. They can be VERY hard to find and sometimes idiotically expensive.

Most IRS's you'll find used are lacking a few critical parts so here's a primer for you. You'll need to have your drive shaft shortened by an inch or get one from A REAL 99-04 cobra, not a GT, a 99-04 cobra cat back or pro-dumps, IRS specific ABS sensor wires (impossible to find last time I looked, go to MPS for that), IRS specific rear shocks and springs. If you need help shoot me a PM.

Stick w/ the solid axle. The Ford IRS was too much of a compromise design due to limitations such as having to fit in stock suspension mounting points and weight (Aluminum case for the diff is not smart, period). Companies like Maximum Motorsports and Evolution Motorsports make great 3 link conversion kits (MM has theirs w/ a panhard bar and torque arm and EM has theirs w/ a single upper link and Watts Linkage). Steeda also has their 5-link system but that requires you to have side exhaust or dumps.

my vote is with beefing up the 8.8...be cheaper

i would recomend doing the swap. you would need a new catback but thats it. everything just swaps over. i dont know what the abs wires that r3d is talking about but when i talked to the mechanic that i fully trust all that needed modification was the ebrake cable.

and get all derlin busings. that is what makes the irs so weak.

This is exactly the information I wanted... I don't want to have to go buy parts every weekend just to keep the rear end going... The sway bars and coil overs are MUCH cheaper even after replacing the shocks/springs... Plus the IRS does nothing for the inherent body roll in that car without doing the rest anyways...

Reliability is extremely important to me, so I know where to start. Thank you for your help.

READ THIS QUOTE
this is a good faq from ac427cobra. he has a lil side business making delrin bushings for the irs. its a real long post but i took what you need to know and posted it here. i would highly suggest reading the whole thing. i know i did a few time over.

http://www.svtperformance.com/forums...d.php?t=260665

irs = autoX and solid = drag? i dunno im lost.

Yeah thats what most use them for.