99 Cobra IRS in 33 Hot Rod?

[99Cobra2HotRod]

I'm retiring my 99 Mustang Cobra (I'm original owner) and plan to use as many parts from it as possible for a 33 Hot Rod kit. Aside from the engine, transmission and some under-the-hood components, would it be possible for me to use the 99 Cobra IRS? It is not listed among the supported configurations on the kit order form. You may view a labeled drawing at www.drivingenthusiast.net/sec-ford/FMC-products/platform-sn95/1999-cobra/specs/99irs-02.jpg . I understand it's not as desirable as the 2015 version but I already own it and this would be a street cruiser with no hard cornering or drag-type starts anticipated. Excerpting a drivingenthusiast.net quote of Eric Zinkosky, Suspension Systems/Development Engineer-Mustang Vehicle Engineering from that era, "The independent rear suspension’s springs and Monroe shocks attach to the Cobra exactly where they did with the solid axle set-up. The only difference between the two systems is the addition of two bolt holes and "weld nuts" near the former Quad-Shock mounting holes. This four-bolt mounting system attaches the subframe mounting brackets to the underbody in a very secure way. And it’s such a match to the assembly tooling that the same machine that lifts the solid-axle suspension for V-6 and GT Mustangs also raises the IRS into place." (Entire article may be viewed at www.drivingenthusiast.net/sec-ford/FMC-products/platform-sn95/1999-cobra/specs/irs.htm .) My primary goal would be to save money, since I already own it. Thank you in advanced for any answers, opinions, suggestions, etc., anyone may like to share.

[Svtfreak]

First let me say that I've had 3 mustangs with that irs and got them all working ok. Two where 500+ whp terminators.
Yes. You could bolt it in and make it work. Selecting wheels will take a little more research to ensure proper fitment. But the basic 4 mounting points for the IRS are there on the FFR mk4 and hot rod chassis. Just order it set up for mustang 8.8" with stock style 4 link.

That's said, I wouldn't do it unless it was strictly to save time and money because it is what you have. That irs was a bandaid to be able to say "it's got an IRS" and needed lots of work. If you do it, minimum, get better bushings at the 4 mount points, diff bushings and add a plate to the rear mount points to sandwich the bushings. All thus minimizes he number of moveable points and helps to lessen wheelhop. Too many dynamic parts was one of the problems with those. Next is springs. You'll definitely want something lighter than for the mustang. That, I've never tackled so can't advise there.

Now, would it be cool? Although a bit clunky and massive, it would be cool. It may ride better than live axle but wouldnever perform or ride like a true IRS system. But it does sound like, I'm your case, if you want a budget build that would be the way to go.

Edit: the quad shock mount plates may not be there on the hot rod chassis, but they would be easy easy to add if not.

[99Cobra2HotRod]

Thank you SVTFreak for making my day! At minimum, I'll retain my IRS when getting rid of the rest of the Mustang and doing my research. I'll have to try to compare images to understand your "chunky and massive" comment (possibly good for street looks?) and will look into the quad shock mount plates issue. Thanks also for the great suggestions for the better bushings and plate for the rear mount points. I may have a friend who can help me on the spring rates. I have not interacted at all with FFR yet. Do you think they'll work with me or should I just assume I make the changes myself, as they sound fairly straight forward by your comments?

[Svtfreak]

When I say chinky and massive, I mean it's just big. Lots of parts and lots of mass. So it's not svelt and trim. If someone looks under the car, it'll look big and bulky, and the parts that are seen may appear larger. Remember the old jaguar irs in t buckets? Same idea.

Anytime on the advice. And yes, it should be a very easy install actually. I don't think FFR would be much help. They pretty much stick to what they design for, and that's understandable. They where not much help when I asked about the teams I want to run. But they can't plan and design for every possible part or build style someone may want. And making the change on the frame yourself would be easy. You can buy all the parts from places such as maximum motorsports or LRS or American muscle might still deal in 99-04 irs parts and follow their instructions. The one off the beaten oth will be the quad shock mounts and that's literally two flat square plates with a couple holes drilled in it. You can get the sandwich places, maybe get 2 sets and build your mount for the IRS with those.

Oh! And buy the bushing removal and installation tool. It will save your Christianity, and quite possibly your marriage, knuckles, sanity, and lower your drinking bill the day you actually address those.