Cobra IRS in 1st gen Fbody?

[Wall]

Anyone ever done this of know of someone that has installed a IRS out of a 03/04 Cobra? They seem to be pretty common and reasonably priced if you are up for the fab work.

[Buryingthesun]

I've been debating it, it's not going to be bad if you can fabricate

[Wall]

Yeah when you look at the price of a 4-link and compare it to buying one of these IRS units it seems like a good way to go. Most 4-links will run you around $1300 or so but you can get a Cobra IRS unit for around $700 and you get a limited slip diff and usually disc brakes.

I wouldn't mind the fabrication and I even though about taking measurements of my car and the IRS unit so I could do a drawing in Unigraphics. I figure this would at least give me a good starting point and I could get a better idea of the best way to integrate it in to my car.

[adibs]

I am also interested in how this would work, is the track width close?

[Wall]

From what I found searching:

Cobra IRS was 62" wheel mounting surface to wheel mounting surface at ride height

67-69 Firebird rear end is 61.25" end to end


So if that is true it is pretty close.

[Wall]

Well it is looking like the 350Z IRS may be a better option, still researching it though.

[adibs]

i heard the 2004-6 gto irs is cheap

[Build-It-Break-It]

There's a member here who's already started a 350z rear end. Looks cool but lots of work. I attached the link below. Hope this helps your research.


https://www.pro-touring.com/threads/84491-350z-rearend-67-camaro

[Wall]

Thanks man! That is a good thread, I would like to see that car when it's finished! I found another thread also where they were installing a 350z IRS in a 71 camaro. I noticed in both of these threads they installed new frame rails but didn't see if that was necessary or not, I wouldn't be opposed to it if it needs to be done.


adibs, I will also checkout the GTO IRS, I did see a few of those on craigslist.

[Number1]

Why not use a 5th gen camaro irs?

[Bob in St. Louis]

I've wondered if anybody has ever used the IRS out of a Japanese SUV.
Like a Honda, Toyota, etc..etc...

[srh3trinity]

I looked into the Gto rear ends since they are cheap and they didnt seem to have the best aftermarket support. With all of the gen 5 camaros out there now, those should be cheap and you can get Brembo brakes on some and upgrade to z28 or zl1 parts if you are making bi power. Cobra irs should have nice aftermarket support too.

[Buryingthesun]

I've wondered if anybody has ever used the IRS out of a Japanese SUV.
Like a Honda, Toyota, etc..etc...

Have you ever looked at one? They use a 4" diff and pencils for axles. . .

[Bob in St. Louis]

Not up close, just what I can see from sitting behind them at the stop light.
I wasn't meaning the Honda CRV and Toyota Rav4 type mini-SUVs, I was meaning more along the lines of the bigger SUVs.
Are they all still pretty small regardless?

[srh3trinity]

To do IRS, I would think you would want improved geometry and packaging amenable to a swap. I would think suv irs would lack both. Kind of like putting jaguar irs in just to say you have irs. You could do a four link for cheaper and likely have a better handling car. Now, some of the other options mentioned above are intriguing to me.

[Bob in St. Louis]

Well, that makes sense. Now that you mention it, I suppose there's certainly a lack of gear ratio options available in a large Jap truck rear end.
Thanks guys for letting me highjack the original question.

[Wall]

I have been doing more research and will continue to. At some point I will start a new thread with all the information I find. So even I end up going a different route at least a lot of the info will be in one place and possibly save someone else some time if they consider an IRS swap.

Here is a quick rundown of what I have found:


5th Gen Camaro IRS: From what I have seen these are a little more expensive than the alternatives (have seen some for around $1000 without the diffs). I'm not sure if all have the 14in rotors but if they do then you would probably have to run a 20in wheel or swap the rotors and fab up a new caliper bracket. I don't know the width on the IRS but the 5th Gens are BIG compared to a 1st Gen so that could be an issue.

03/04 Cobra IRS: You can find these reasonable ($600-$900). They have limited slip and pretty good brakes. They will handle a good amount of power if you upgrade the bushings. These IRS units did suffer from wheel hop which was mostly caused by binding in the stock control arm bushings. Also the mounts for the diff had a lot of compliance which allowed the diff to move too much during acceleration and could cause the half shafts to be at more extreme angles. But depending on your power levels and what you intend to do with your car this may not be an issue.

350z IRS: Prices on these seem to be pretty good ($300-$700). They can take a good bit of power, not sure the exact amount but I did fined where guys said they were running turbos and sub 10sec 1/4 mi times with stock IRS units. There is a lot of aftermarket support for these IRS units. You will need wheel adapters since these are 5x114.3mm and to fit the cradle in a 1st Gen you will have to modify or possibly fabricate new frame rails.

05/06 GTO IRS: These seem to be reasonable ($500-$750). Looks like it may be relatively easy to install in a 1st Gen. But this IRS is a semi trailing arm setup which isn't horrible but you don't get the benefit of camber gain when the suspension compresses. Camber gain will help keep the tires more evenly planted in the corners.

BMW IRS: I am just now starting to look at these so I don't have much info. I do know that there seem to be a lot of BMWs out there that are being parted out and BMWs tend to handle pretty well so I figure I will see what info I can find.

[k5warwagon]

I'm leaning toward one of the two options below for my '92 S10.

This http://team321.com/truckirs/truckirs.html
with a IRS from a Lincoln Mark III

Or one of these with a C4 D44
http://www.streetrodgarage.com/c4corvetteirsrearcradlekit.aspx

http://team321.com/truckirs/truckirs.html

[adibs]

no camber gain on the gto irs is really off putting to me so i wont go with that

[Wall]

no camber gain on the gto irs is really off putting to me so i wont go with that

Yeah me too. I would hate to go through all the trouble of putting an IRS in and not get the benefit of camber gain.

I did find a Lincoln LS IRS local for a good deal. I am seriously considering it but I will need to take some measurements when I go look at it. The only thing that is making me think twice is the control arms mounting points are forward of the axle center-line and this seems like it would limit wheel/tire width. Here's a reference pic.


101041

[adibs]

yea i see what you mean, but it looks like you got at least 6 or 7 inches of back spacing. however it does look like it would be easy to install! just fab up some mounting points off the rails.

[ace_xp2]

I feel I should add that semi trailing arm suspensions do have camber gain, the issue is that they also toe in at the same time, so their is only so much gain you can get away with before toe becomes a major issue. Packaging them into old suspensions is kind of nice because they're generally low slung. If the handling compromise is worthwile to someone versus the comfort gain, maybe look to the system from the e34 bmw 5 series, it uses an additional tracking link to, I believe, help with toe and allow for more camber gain.

[Wall]

I feel I should add that semi trailing arm suspensions do have camber gain, the issue is that they also toe in at the same time, so their is only so much gain you can get away with before toe becomes a major issue. Packaging them into old suspensions is kind of nice because they're generally low slung. If the handling compromise is worthwile to someone versus the comfort gain, maybe look to the system from the e34 bmw 5 series, it uses an additional tracking link to, I believe, help with toe and allow for more camber gain.


Thanks for the info! That does makes sense, I can see how the trailing mounting point locations would affect camber and toe.

[latamud]

I have been doing more research and will continue to. At some point I will start a new thread with all the information I find. So even I end up going a different route at least a lot of the info will be in one place and possibly save someone else some time if they consider an IRS swap.

Here is a quick rundown of what I have found:


03/04 Cobra IRS: You can find these reasonable ($600-$900). They have limited slip and pretty good brakes. They will handle a good amount of power if you upgrade the bushings. These IRS units did suffer from wheel hop which was mostly caused by binding in the stock control arm bushings. Also the mounts for the diff had a lot of compliance which allowed the diff to move too much during acceleration and could cause the half shafts to be at more extreme angles. But depending on your power levels and what you intend to do with your car this may not be an issue.



I did a lot of research on IRS before I settled for the 03 Cobra setup I did in my 66 mustang. I'm commenting because I did cometo the same conclusion as quoted above. There are fixes for this but agree: the rubber cradle bushings, two forward and two upper rear, the two front diff bushings and tghe rear diff bushing, two each upper and lower control arm bushings allow the IRS to move slightly in every which way that will defeat the benefit of the IRS. There are fixes for this. In a custom setup, I welded in solid mounting points to the Cobra IRS cradle to mate to my frame rails. I added solid front and rear diff bushings as well as a rear diff brace plate. Currently still running the stock rubber control arm bushings but I think that is a clean compromise considering I've statically mounted the cradle and diff, they won't move, so that lets the half shafts and the control arms do their job.

There's also a Poly/Delrin bushing kit from Full Tilt Boogie that will also replace the bushings, but again, in a custom application, you decide how the unit will mount under your car. What I like about the 03/04 IRS kit, it already handles the power and torque you probably want to put through it. After my research, I ended up snagging 4 Cobra IRS drop outs for other projects. The car handles so much smoother. In any case, I don't think you can go wrong with any IRS kit you go with. Each will have its own benefits and flaws.