Ideal IRS System Discussion

fastsc92

Registered User
I'd like to hear people's thoughts on an "ideal" IRS system. If you could have any features for an aftermarket system, what would they be?

All new tubular components?
Utilizing all stock component?
A mix between the two?

Upper control arm with two mounts to the frame?
Using Cobra Rear Spindles?
Coil-over system?
Additional camber adjustment?
Improved Roll Center?

I'd like the hear everyone's thoughts and get a serious discussion going...
 
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One would be a replacement tubular IRS cage..That would cater to most

The other would be an all out one for handelling. New tubular everything..

Now if we could adjust for bumpsteer that be niicceee
 
chrome-moly subframe that will fit stock control arms with the option of tubular steel upper and lower control arms, possibly switching to a a-arm for the upper control arm, if it can be made to work. Get some stabilization in the upper part of the knuckle.
 
Pretty much what has been said already.

Tubular irs subframe, tubular upper A arms, double adjustable, lower tubular arms, adjustable on all 4 corners, coil overs. Solid mounting of subframe and diff. Shorter sway bar end links that are adjustable. I guess the biggest thing is being able to adjust caster, camber, toe, bump steer and all the other suspension measurements I don't understand. Half shafts are available now as well as a diff cover with girdle built in.

How about shorter half shafts and control arms to pull the spindle in to fit a wider tire? A mini tub kit would be nice too. Some type of bolt in or even weld in subframe connector. All of this commercially available is what I mean. I could go on and on.
 
A bolt-in design is key. I have my thoughts from an engineering point of view on what features it should contain, but I'm still looking to hear what others might want.

It's possible that their might be two designs. One that could be used for general purpose, geared towards handling, and the other geared towarded straight line performance. The instant centers of each suspension could be different. Both solutions would be able to fully adjust for camber and toe. Theoretically, anything can be designed, but I'm more interested in the majority vote here.
 
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My thoughts are if you want to go straight, for the money you will put into tubular, adjustable irs components you could build one heck of a straight axle.

I think the market would be much bigger for something suited more for handling or street driving, just because there are more mn12 owners in that category. I also think that a well designed suspension should be able to have some adjustment built in to tune it for the drag strip.

I can tell you that my next mn12 build will be set up more for road racing/autocross and handling than my last one which was set up more for the drag strip.
 
I would not be interested in a setup that deviated drastically from the stock setup. Ford put a lot of effort into the system and we'd be fooling ourselves if we thought we could improve on it just that easily. I would want a tubular setup that accepts all the stock mounting points and upper/lower control arms. I would even like the option of running the toe link.
 
A bolt in stock everything IRS cage like I said would sell best. Upgraded componants to fit that cage could then be fabbed that may even be able to be used with the stock frame. You would sell the most that way...

Regardless the you wouldnt be wasting your time fabbing a stock replcement cage and could probably sell as many as you can make.

Now Ford had a few variations of the rear IRS setup from what I understand and what we have in teh mn12 is a product of value engineering. Duffy may have more info on this or one of his buddies. Why engineer something when something that has already been tested and known to work can be fabbed up.
 
good info...thanks guys

I would not be interested in a setup that deviated drastically from the stock setup. Ford put a lot of effort into the system and we'd be fooling ourselves if we thought we could improve on it just that easily. I would want a tubular setup that accepts all the stock mounting points and upper/lower control arms. I would even like the option of running the toe link.

Ford def. put in the time during design. Comparing our IRS to that of a Cobra, I feel that we have a better design. Mainly because ford was tasked with fitting an IRS subframe into a car with pre-designed mounting points for a solid axle.

What I think might be beneficial is using the same relative position of the upper CA mount, but make it an a-arm design. How camber is adjusted...who knows. Possibly switch to a set-up that uses an ecentric bushing in the knuckle, or another clever design that makes adjustment easy without unbolting rod ends.

Personally, I think that the lower arms are fine in their stock state. Making something tubular with the strength required, spring pocket, etc. would most likely result in a heavier set-up than stock, and with the availability of aluminum arms, i would like to see it go that route. Coil-overs could be an option, but I'd like to see the upper shock mount area strengthened before installing a set.
 
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I will go out on a limb here and say it. A STABLE upper arm that reduces the for and aft movement of the upper arm. I am building a trailing arm system for mine to eliminate the hop. I am also cutting/slicing the main rails and welding them solid to make it lighter and stronger at the same time.

Also if a coil over could mount in the stock position with a ligher LCA, that would be noice.

SWS
 
I think a coil over shock would work better where the spring is now and eliminate the outboard shock. I think by removing the upper spring perch a bolt on shock mount could be installed and it would work better than the outboard shock position. You would also gain a ton of tire clearance. It would take some time and careful measuring and a good shock catalog with dimensions but it wouldn't be that hard
 
My only interest would be in a kit to convert over to the larger diameter Cobra half shafts, but still retian the existing bolt pattern and rear brakes.

David
 
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Although an upper A-arm would be a benefit with the stock rubber bushings, I doubt that you'll be able to fit one with the correct geometry, without interference from the body (the reason the stock upper arm is curved). Perhaps a curved upper A-arm would be possible, with an outer threaded adjustment for camber.

With improvements that are already available, the stock suspension is far better than the Cobra IRS (which had to be shoe-horned into the available space).

A tubular replacement, with significant weight savings, using the stock geometry and attachment points would be nice. Better body mount bushings would also be helpful.
 
My only interest would be ion a kit to convert over to the larger diameter Cobra half shafts, but still retian the existing bolt pattern and rear brakes.

David

It would def. be nice to stuff a set of cobra half shafts in there. This seems like it would push the hubs inward by .9" on each side. I know the measurement differences between the SC and cobra shafts are floating around here somewhere....

DLF,

Yes, the upper arms would have to be curved in order to clear the frame during its travel. The cobra guys have this option available for tubular uppers. I guess it could be possible to do something similar and have a single threaded adjustment/turnbuckle right before it attatches to the knuckle.

m5lp_0609_irs_10_z+irs_fox_body_mustang+control_arm_test_fit.jpg
 
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Or more

Looks like the Cobra half-shafts are more like 1.75" shorter....
 

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A previous post already pointed out that cobra half shafts could be used by some adjustment to the CV joint locations. Here is the thread:
http://www.sccoa.com/forums/showthread.php?t=52799

If you noticed in a recent hot rod issue, they discussed what GM did with the Camaro rear subframe to curb wheel hop. The driver's side half-shaft is shorter than the passenger side half shaft. Some pictures are in this thread, as well as discussion http://www.camaro5.com/forums/showthread.php?p=271188

if you do it right, you may also be able to sell something like this to Factory Five folks who have used MN12 IRS assemblies in the past.

Consider also replacing subframe bushings with this process so we can tighten things up.
 
- I haven't installed the Delrin in my car yet, but based on what Doug and Damon have testified to, there shouldn't be any real need to use an A-arm on top. The lower control arm design, if we retain that, is strong enough to control oscillation motion without an upper arm for support. I like this idea, keeping the heavy control arm down low and leaving the upper relatively light weight.

- I like the OE camber bushing. It is low friction and easy to obtain precise adjustment. I do feel that additional camber adjustment is needed on lowered cars. This could easily be achieved with a custom upper arm. A piece of curved chrome moly would be sweet here. It could have an adjusting nut in it for rough setting and then the OE bushing used for final setting. The CM arm could be very lightweight and an add-on for those who wish to spend the extra.

- I don't feel any need for bushings in the subframe mounts. I have welded those solid in the past and it does not cause noticeable NVH. Because the IRS subframe is currently bushing mounted, it has to have enough structural rigidity to retain shape under load without body support, and the body likewise cannot rely on the subframe for support. By making the IRS subframe solid to the car's frame you can greatly strengthen both. I think this is a BIG available benefit. Again, solid bushings do NOT result in noticeable increases in NVH.

- Rear sway bar mounts could obviously be strengthened.

- More room for exhaust routing would be a plus.

- Using the Cobra axles doesn't seem like much of a plus to me. As far as I know the outer hubs are the same as ours, they just have the 31 spline inners, and without changing the track of the rear there just isn't any way to use the axles themselves without stretching out the joints as Doug pointed out. I don't think the hub end of a Cobra axle is any different than ours.

- I'd like to see a provision for axle loops. I believe these are required on IRS cars in the 9's.
 
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