IRS an advantage for Drifting/Autocross/Open Track? Disadv. @ Drag Strip?

Justin_Bradley · Apr 2, 2007

I am trying to build a 5.0 up that can have respectable performance everywhere and in any type of competition I may want to enter. I know I'm going to have to reach a median performance level with things such as gearing, clutches, springs and shocks (may actually have different sets of these for each type of competition), etc.

This is not what this thread is about. I have read that there are major gains in traction and predicting the driveability of a car with an IRS system during road course and drifting events over one with a solid read axle. I have also heard there are major drawbacks when it comes to drag racing with this system. However, I've read of numerous street '03-'04 Cobras going well into the nines, which is about 1-2 seconds quicker than I want my street Stang to be able to go. I would be pulling the system from an '03-'04 Cobra and putting it into a '94 5.0.

So, is the swap worth the $XXXX it's going to cost? Also, is this something that will bolt right up (I assume the chassis of a Cobra is no different than a GT)?...

Dalamar · Apr 3, 2007

well Justin, I'm not an expert on this, but will explain what I know.

The IRS is nice for moderate driving and moderate power levels. It is a smoother ride for sure.
A lot of drag guys, swap out their IRS for solid rears BC hard launching will mash the bushings.
MM makes better bushings for it you can swap out, but it's more $$. and you still get wheel hop.
you also have to re rought your exhaust if you swap to an IRS.

Keep in mind the stock suspension setup, IRS or 4-link has problems.
the 4-link uppers cause bind and there is too much sway from the stock bushings.
they were not desgned for racing. they were designed for 2-300 hp street driving.

Suspension is a complex subject.
If your goal is drag racing, a beefed up solid axle would probably be best.
If you want all around performance, I'd look at the Torque arm, 3-link design. that's what I put on my car.

I also suggest you call Maximum Motorsports and talk it over with them. they KNOW suspension

Thomas_W · Apr 3, 2007

I swapped the solid rear out of my 96 for a 03 cobra rear FOR FREE. if you look enough you'll find someone who will swap straight out w/ no or little $$$ invovled. That said. I will NOT go back to a solid axle. turns that i couldn't take at 70mph before w/ the solid i take at 90-95 mph now w/ the IRS. It rides better, it handles curves better. Hell it does everything better that i have thrown at it. There are many guys cutting 1.6 60' on the IRS also, you just have to learn to drive the car again to do so. And if you upgrade to DSS level 5 1/2 shafts its even better.

Lightning Struck · Apr 3, 2007

Dalamar said:
well Justin, I'm not an expert on this, but will explain what I know.

The IRS is nice for moderate driving and moderate power levels. It is a smoother ride for sure.
A lot of drag guys, swap out their IRS for solid rears BC hard launching will mash the bushings.
MM makes better bushings for it you can swap out, but it's more $$. and you still get wheel hop.
you also have to re rought your exhaust if you swap to an IRS.

Keep in mind the stock suspension setup, IRS or 4-link has problems.
the 4-link uppers cause bind and there is too much sway from the stock bushings.
they were not desgned for racing. they were designed for 2-300 hp street driving.

Suspension is a complex subject.
If your goal is drag racing, a beefed up solid axle would probably be best.
If you want all around performance, I'd look at the Torque arm, 3-link design. that's what I put on my car.

I also suggest you call Maximum Motorsports and talk it over with them. they KNOW suspension

Jeff gave a good account for the IRS, but I would like to add that you CAN make the IRS wheel hop free. You just have to get the right parts to do it with, then if you still have stock axles you risk breaking them, so you should step up to some srong aftermarket ones. The IRS is what I would run on a street car that will not be a NORMAL track car, or one that you plan on beating on, on a pretty regular basis. Mine is fine in my 99 Cobra because I dont dog it and it only sees full throttle once in a blue moon.

Justin_Bradley · Apr 3, 2007

So I don't have to search around forever, I have two quick questions:

Dalamar:

Does the Torque arm take the place of the upper control arms or lower control arms on a solid rear? Or Both? Or neither?

Thomas_W:

Was the swap pure bolt in or did you have to weld in some mounting brackets?

Dalamar · Apr 3, 2007

the torque arm replaces the uppers.
the lowers stay.

Hybridbird · Apr 4, 2007

I saw a GOOD tech article where two guys bolted a Cobra IRS into a Fox Mustang.I don't *remember* any cutting or welding,just a BFH for clearance in a spot or two and drilling a few new holes for bolts.I don't see why it couldn't be done in one of our cars if they did it in a Fox. :dunno: I will see if I can dig up a link for you,if it's still around.Here ya be....

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

Justin_Bradley · Apr 4, 2007

Hybridbird said:
I saw a GOOD tech article where two guys bolted a Cobra IRS into a Fox Mustang.I don't *remember* any cutting or welding,just a BFH for clearance in a spot or two and drilling a few new holes for bolts.I don't see why it couldn't be done in one of our cars if they did it in a Fox. :dunno: I will see if I can dig up a link for you,if it's still around.Here ya be....

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

Good article. Appears to be a lot easier than I thought it would be.

Thomas_W · Apr 4, 2007

Justin_Bradley said:
So I don't have to search around forever, I have two quick questions:

Dalamar:

Does the Torque arm take the place of the upper control arms or lower control arms on a solid rear? Or Both? Or neither?

Thomas_W:

Was the swap pure bolt in or did you have to weld in some mounting brackets?

It was a straight bolt in for 99% of it. The 94-98 cars dont have 2 of the bolt holes for the rear IRS subframe mounting brackets. So you can either 1. Drill these holes and bolt the bracket in place. or 2. Bolt the bracket into place w/ the 2 bolt holes you do have (which are also the quadshock mounting bracket bolts). And then weld the lower portion of the bracket in place. This is the route i took b/c i dont plan on removing the IRS.