Cobra IRS Swap
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OnyxCobra
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ReplicaR :notworthy: 
ccasion14:
ccasion14:Goindeafonmtx
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I've done the swap, but for completely different reasons. My suggestions, go test drive a 99-04 Cobra, preferably in stock form. Pay attention particularly how it rides. I know my impression is how smooth they are. If I were looking for comfort, there is nothing better than the IRS.
The install is really not bad. The hardest part is the brake lines. I'm using stock style lines, but I bent them to fit and I had to relocate the mounting point on the subframe rail to avoid being crushed by the upper control arm under compression. Make sure you take you time, and have a friend to help. Its a heavy unit and you don't want to hurt yourself. You don't need to drop the gas tank completely. You just need to move it enough to drill 1 hole for the rear mounting bracket.
As far as performance, I am very pleased with my results so far. I have only used the car for autocrossing so far, so my experiences don't speak to open tracking. I installed Bruce's complete bushing kit before I put the IRS in the car. I also ran MM sport valved Bilsteins with a 650lb spring, so the rear is very stiff. So stiff to the point you would never know that the IRS is even in the car while on the street. As far as autocrossing, adding the IRS is the best thing I have ever added to the car. Their is an SN95 car with a complete t/a, ph bar setup, and MM style K at the local autocross events. It is bona fide race car with nothing but a seat and a steering wheel; no interior, nothing. The guy driving used to drive in NASA and is the chapter driving instructor, so he is no slouch. My car is a complete street legal car with complete interior, stock K and is at least a second faster at every event. I might be missing something, but to me, the IRS can be made to be a superior to that of a built SRA and that is proof. And it was a pretty damn easy and cheap.
The install is really not bad. The hardest part is the brake lines. I'm using stock style lines, but I bent them to fit and I had to relocate the mounting point on the subframe rail to avoid being crushed by the upper control arm under compression. Make sure you take you time, and have a friend to help. Its a heavy unit and you don't want to hurt yourself. You don't need to drop the gas tank completely. You just need to move it enough to drill 1 hole for the rear mounting bracket.
As far as performance, I am very pleased with my results so far. I have only used the car for autocrossing so far, so my experiences don't speak to open tracking. I installed Bruce's complete bushing kit before I put the IRS in the car. I also ran MM sport valved Bilsteins with a 650lb spring, so the rear is very stiff. So stiff to the point you would never know that the IRS is even in the car while on the street. As far as autocrossing, adding the IRS is the best thing I have ever added to the car. Their is an SN95 car with a complete t/a, ph bar setup, and MM style K at the local autocross events. It is bona fide race car with nothing but a seat and a steering wheel; no interior, nothing. The guy driving used to drive in NASA and is the chapter driving instructor, so he is no slouch. My car is a complete street legal car with complete interior, stock K and is at least a second faster at every event. I might be missing something, but to me, the IRS can be made to be a superior to that of a built SRA and that is proof. And it was a pretty damn easy and cheap.
While your comparison may be valid to some, I think there are a quite a few massive pitfalls in your logic. You are comparing the cars that are completely different. You did not mention what tires are you and your competitor running, what classes the cars are in (I seriously doubt that a "bona fide" race car and a street car will be running in the same class), how modified is the engine (power to weight), and more importantly, the driver difference. I'm running with NASA as well, and I instruct for two groups myself. I've never once done autoX, and I've got a feeling that if I'd ever try it, I'd suck, because I'd probably get lost in the cones.
Unless there is a test where an IRS is swapped and tuned into a solid axle car, and that reduces times or picks up grip, I really doubt that under same conditions (read: same vehicle) IRS will outperform a Torque Arm car. Another thing I'd like to bring up to your attention is the fact that just about every car that's running AIX and AI is running a solid rear. Think about it for a second. These are cars that cost somewhere around 70k per car to make, and there are virtually no limitations. Why would most of those cars, including people who took nationals, regionals and set track records run SRA?
Unless there is a test where an IRS is swapped and tuned into a solid axle car, and that reduces times or picks up grip, I really doubt that under same conditions (read: same vehicle) IRS will outperform a Torque Arm car. Another thing I'd like to bring up to your attention is the fact that just about every car that's running AIX and AI is running a solid rear. Think about it for a second. These are cars that cost somewhere around 70k per car to make, and there are virtually no limitations. Why would most of those cars, including people who took nationals, regionals and set track records run SRA?
+1 ReplicaR :notworthy: ccasion14: and WMM FTW!!!!
ccasion14: and WMM FTW!!!!Goindeafonmtx
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Well, most of what you find a pitfall in my logic I left out due to time(past my bedtime) and I was trying to be brief. So to start with, both cars on street tires. Although, mine were a little more aggressive. As far as classes, he runs his car in C prepared, I run Street Modified. His class is dominated by "bonafide" purpose built race cars, mine street cars. As far as drivers, he is no doubt a better driver than me, simple as that. In my opinion, I'm still green to autocrossing as I just completed my first full year. If I remember right, his car is around 2600-2800lbs with a 302 ran on megasquirt. Mine is around 3400-3500lb I'm guessing by looking at others, and a completely stock b headed dohc(dynoed at 293 last year). His car has all the advantages.
You are completely right as far as the best comparo would to take the exact car and set it up one way then the trying the other. But that is money and most of us are not made of it. It really comes down to preference and how comfortable one gets with a particular setup. I need to bring to your attention to the fact that every "real" performance car(I say real because you and I both know Mustangs were not designed to be used in the manner in which we use them) has an IRS and not a stick axle. Just because people do not use an IRS doesn't mean it isn't a viable performance option. People do what they know, and shun everything else they don't understand. The Mustang road racing crowd has millions of dollars and 40+ years invested in developing the stick axle. I see it as a way of saving face and just condemning something they don't understand or want others to understand.
You are completely right as far as the best comparo would to take the exact car and set it up one way then the trying the other. But that is money and most of us are not made of it. It really comes down to preference and how comfortable one gets with a particular setup. I need to bring to your attention to the fact that every "real" performance car(I say real because you and I both know Mustangs were not designed to be used in the manner in which we use them) has an IRS and not a stick axle. Just because people do not use an IRS doesn't mean it isn't a viable performance option. People do what they know, and shun everything else they don't understand. The Mustang road racing crowd has millions of dollars and 40+ years invested in developing the stick axle. I see it as a way of saving face and just condemning something they don't understand or want others to understand.
Goindeafonmtx said:
This is why I find it so hard to believe. To me there are only two possible explanations for that. Either, you can drive better than him, or you have a MUCH more aggressive tire. Tires are responsible for most handling anyway. There is no way in hell IRS would compensate for a 700lbs difference, and a car that's very well setup with proven performance parts (currect AIX national champ Chris Griswold is running MM)
I never once said that a well designed IRS rear would be outperformed by a solid axle. As a matter of fact, I did mention that BMW has a much better designed rear suspension than both of Ford's rears. Believe me, if I could afford to run a competitive BMW, I would have never bothered with Mustang in the first place. What I said was that the cars in American Iron and American Iron Extreme (Camaros, Mustangs, FFR) have more success with the solid axle. There are people who are running IRS on some mustangs, but they don't do nearly as well as solid axle guys.
Ford is capable of designing a bitching IRS and a really good chassis. They've done so many times in Europe with cars like Escort (old generation, newer Cosworth), Sierra Cosworth, and even Falcon back in the 60s was a great car. I'm just saying that as far as the Mustang goes, IRS is not the most proven setup.
I think the most important thing if you're going to be racing is, Know how to drive, Know your setup and don't go cheap when you mod. The most important thing is to know how to drive. :0) Second most important thing is to know the modifications and it's limitations. The ford IRS design pretty much sucks (They should have taken a cue from their brother Jag) but it can be made to do what you want. I road raced my 73 Nova with a Jaguar IRS for years and loved every corner of it. :0)
ReplicaR said:
OP
OP
I like potatoes and appreciate everyone participating in my thread..... group hug :boxing:
Goindeafonmtx said:
I agree with this 100%. Some guys can probably drive the crap out of an IRS car, and some others will be better with a solid axle setup. To each his own.
I would go with the most cost effective route, either way.
pp_puncher
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I had a 04 cobra before I lost my job last year, and at first the IRS was a pain. I seemed to wheel hop every time I spun the tires. After a moth or so, I put sub frame connectors on (welded) and no more wheel hop. If you do decide to do the swap I recommend doing gears, IRS bushings, IRS 8.8 girdle, and sub frame connectors at the time of install. Also keep in mind that the 99 cobra has 28 spline axles and 01+ have 31 spline. With all of that being said, it was nice when I had it, but I don't miss it.
