View Full Version : Teaser on one of my current projects..

Chuck W
01-30-2005, 05:46 PM
Hey guys. Just a couple pics of one of my current projects....an IRS for a Fox-chassied car.

This is the "pre-production" mock-up. We're still getting things added to it and getting all the bends and notch angles, etc sorted out before we build the "real" one (thus the butted together tubes you see). We still have a fair bit to do, and the next task is to get the differential mounts located.

No details on whether we might produce them or not, but we'll make at least 2 ;) (one for my car and one for his). It is a totally new geometry..not a rehashed Cobra set-up. We are planning on making use of the Cobra spindles for now.

Enjoy : :grinno:

Orange Crush
01-30-2005, 06:12 PM
Cool!! :headbang:

01-30-2005, 06:34 PM
pretty awesome...

01-30-2005, 09:38 PM
Cool idea man but wouldn't it be easier to just get the complete irs suspesion from a newer stang?
I read an article(can't remember the site)about the irs from a stang bolting in to the car with just a few mods to the chasis,nothing major just time consuming,you don't need to modify the suspension at all,minor notching and a few holes to be drilled in the frame and it bolts up like factory.

01-30-2005, 09:53 PM
Cool Idea. Here is the site for the IRS SWAP


Chuck W
01-30-2005, 10:13 PM
but wouldn't it be easier to just get the complete irs suspesion from a newer stang?
I was waiting for that...

I'm not looking for the "easy"....I'm looking for the better.

Obviously I could have taken the Cobra route, but I was never that impressed with the Cobra IRS to begin with. It was ok for what it was, but they could have done so much better if they had actually been able to design it the right way. Stock, it is a very compromised set-up as they had to make it fit in place of a stick axle and use all the same mounting points, etc. It's also much heavier than it needs to be by the way they have to beef it up to handle the mongo springs they have to use to get any kind of decent wheel rate out of it.
We are using the Cobra uprights and the diff, but everything else will be new.

Thunder Chicken
01-31-2005, 08:10 AM
Would a Cobra IRS even bolt into one of our cars? If the upper and lower control arms are different (which they are), wouldn't this make it so that the mounting points for the Cobra IRS are all wrong?

Chuck, that is awesome - I only wish I had the resources to do what you arte doing! You could probably make yourself rich if you produce that IRS setup - not only would non-IRS people want it, but Cobra owners would want it as an improvement over their stock setup. Street rod builders would be all over it as well - you should certainly get some patents! Of course if my suggestions above are correct, you might have to build two different ones - a T-Bird/Cougar model and a Mustang model (or have adjustable mounting points)

Chuck W
01-31-2005, 08:30 AM
The Cobra IRS would work under a Fox TBird/Cougar with some mods. Mainly to the attaching points at the old control arm points.

On this one, the only forseen issue is moving the front mounting point forward just a touch to allow it to reach the stock LCA mount in the chassis. The rear upper point is making use if an existing hole on both chassis as a general locator. We're actually attaching through the frame at that point. We're not as concerned about making it TOTALLY bolt-in. A couple small "mods" to the chassis are considered acceptable.

I think my buddy would like to possibly sell them, and if things work out well then we might. It's going to take a step up in the facilities we have to make any more than a couple at a time. We're already going to farm out some of the flats to be lasered and might even have the couple tubes we need bent CNC bent to assure uniformity. The bender works fine, but if we get to "producing" I'd rather not waste time drilling and cutting out brackets and making sure we bet every bend spot on each time.

01-31-2005, 11:41 AM
wow! that's... pretty... insane! wish i had the know how to make another part i deemed inferior. *hat's off* can't wait to see the finished setup. ^_^

01-31-2005, 12:11 PM
That's frickin amazing, I love it! The guy you're working with wouldn't happen to be a big Mark VII nut, would it?

Chuck W
01-31-2005, 01:07 PM
The guy you're working with wouldn't happen to be a big Mark VII nut, would it?

Nah, he's a Mustang guy. Well, not really even a Mustang guy, but a guy who likes to do open tracking and such and the Fox Mustang platform is a cheap base to work with.

Don't get me wrong, the Ford piece is a nice one for the constraints they had to work under, but I'm not hindered by them and thus can do what ever I feel like ;) If they were actually able to run free with it I have no doubt it would have put most to shame....but.....

Thunder Chicken
01-31-2005, 04:01 PM
OK, Chuck - 'nuther few questions: You say you're using Cobra uprights and pumpkin. Would it be possible to use MN12 parts? How 'bout half shafts? There are a lot more MN12's around than Cobras, and V8 MN12's had 8.8" rears (Mark VIII even had an aluminum housing). It would be much cheaper and easier to find an MN12 in the junkyard...

I can tell you this: If you were to produce this thing, and keep the price reasonable (maybe $1500 for the barebones, find-your-own-uprights-and-pumpkin kit) I would make it my goal in life to own one. I don't give a rat's ass about drag racing, I bought my car for its comfort and reasonable handling (given the period it was manufactured). I loved the way my old MN12 handled (heavy as it was) and would love to turn the Fox T-Bird into a better corner-carver. The IRS would be a definite improvement over the live axle on our severly neglected roads, too. Combine that with a tubular K-member and coilover kit , and toss a set of aluminum heads and a 5-speed in and I'm getting all wet thinking about it. Think of the weight loss that would create! Even if your IRS was heavier than the stock live axle, it's weight in the right place

Chuck W
01-31-2005, 04:16 PM
The Lincoln and Cobra center sections are the same. There are also iron Tbird 8.8's (IIRC). The gearing would need to be handled by whatever the person wanted/needed, and since they're Ford 8.8, the possibilties are pretty abundant.
While there might be more MN-12 uprights in the j-yard..they are not what I want (made for a "H" lower and "I" upper arm) and it would be more work to bolt up decent rear brakes and the hubs would have to be modified to accept the different bolt pattern hubs (unless they swap directly, but I don't think they do). You can buy Cobra uprights new if you have to...with new bearings and hubs. Not "cheap", but still cheaper than doing something all new up front.

Manufacturing "new" uprights are a possibilty. The Cobra ones are causing me to have to make a few minor compromises geometry-wise, but even buying new ones are cheaper than trying to design and fab something new up to get the car rolling. In the future we might do different uprights and change the control arms accordingly. I'm also getting bugged to look at a dropped SN-95 type spindle (so as to not loose suspension geometry when lowering the car).

01-31-2005, 10:35 PM
I have a 90 Mustang and I will be installing a 01 Cobra IRS in it. Couple of problems with the factory piece. The bushings throughout are simply like jello. What you need to do is replace the subframe bushings of the IRS with poly's and the control arm bushings with Delrin ones. Problems solved. Next this sucker is HEAVY! Most of us can move a solid axle around but not this thing! The best thing you could do Chuck is make the subframe aluminum and make the control arms out of tubular steel.

Its heavy but the weight factor will give you a close 50/50 weight ratio when you bolt it into a Mustang. Like the link posted earlier, they will bolt right up. Some small welding, cutting and drilling is necessary but for the most part it goes right in.

Chuck if you could make the subframe light or even make lighter, stronger control arms you would have a market for sure. Ir reasonable I would buy them.

Chuck, on your IRS. If you decide to go with an 8.8 center section then you have two choices, 28 or 31 spline. All 01 and up Cobra's have 31. The 99 Cobra has 28. I am not 100% sure but I think the Mark 8 has 28 spline as well. At the bottom of this page, FRPP (http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=225) you will see the footnotes stating the splines.

James :)

Chuck W
01-31-2005, 10:57 PM
James...you bring up two of the "compromises" the factory designers had to work with...NVH issues and the beefiness required because they had to use monster springs in it to get any kind of wheel rate. I've worked with the Cobra IRSs before...

This one will be somewhere between the Cobra IRS and the stick axle in weight I would imagine.

We're going with solid frame mounting points, delrin control arm bushings and poly diff mounts on the initial units.

I'm also aware of the spline differences as well. We'll probably work ours up for 28 spline initially.

01-31-2005, 11:02 PM
Didn't they use the higher rate only because where they could fit the spring to the leverage of the arm?


Chuck W
01-31-2005, 11:18 PM
Yup. Since they had to make them a direct swap for a stick axle...the spring perches in the body had to remain the same. They are in a LOUSY location. The rear spring rates are close to that of the front. That's why all the parts associated with them are so heavy and overbuilt. Aftermarket rear springs are even heavier....

01-31-2005, 11:31 PM
Coilover would be the best route as you already know. I had an idea of welding the subrame to the car to make it as one but I don't know if I can access everything when it is in there permenately.


01-31-2005, 11:33 PM
you bring up a good point chuck, i was looking into that cobra IRS swap for a fox and thats one of the major things i didnt like about it, cauzing everything to be so bulky and comprimized. id like to look into what your makeing now, for a future car im planning on building.

Chuck W
01-31-2005, 11:40 PM
We're not going to weld the subframe into the car, it will be bolted. We are also looking at coil-overs as well. Our control arms are going to be stout though.

We're more worried about what we want out of this and not neccessarily the profitable prospects of it. We're aware that they might be there, but that is a secondary concern.

01-31-2005, 11:41 PM
Nate I'am still going to put the IRS in and see how it does. From talking to people who have an IRS Cobra, they said it has a far better ride qualtiy then the solid axle. If I don't like it I will go back to the solid axle and get a watts link.


Thunder Chicken
02-01-2005, 06:28 PM
We're more worried about what we want out of this and not neccessarily the profitable prospects of it.

Now if only we could get some engineers at Ford (and GM) thinking like that...

Chuck W
02-01-2005, 06:46 PM
The thing is..engnieers do think like that..but they rarely are the ones who get to call the final shots....