IRS equipped 83. Need rear swaybar/coil over options.

[Mr Joshua]

Coming this close to finishing my IRS swap in the 83 with the full compliments of FTBR's bushing setup. I need to find a worthwhile swaybar and coil over setup for the car. I've searched and searched to see what swaybars and coil over setups people have used. As far as swaybars go I haven't found any real concrete evidence of anyone using anything but stockers. What would be the best swaybar to use on AI/X courses and the like for my car(see sig). I'd guess (as I haven't weighed the car) that it'd be somewhere close to 3200. Alum headed 357W(437hp/419ftlbs), T56, IRS(3.55/3.27??), SS fuel tank, dash, sans interior plastics, sans door panels, sans sound deadner, factory front carpet, PS, non/AC. It does not have a cage or subframe connectors at this point (held off trying to decide between PHB/TA and IRS). I plan on doing through the floor subframes and a professionally custom bent compliant cage. I also have a burning passion to do either a Griggs or Agent 47 SLA front end or MM/Griggs SLA combo. So I’ll more than likely be switching to an adjustable front swaybar or possibly an SN-95 front swaybar. As clearance in the front might become an issue.
Now as far as coil over’s go, it seems to be between MM and Griggs. I'd prefer to go with Griggs for the coil over’s as they use a heim joint on the lower attachment point where MM uses a bushing style lower attachment point. But, if I can get some decent info about one vs. the other it'd be greatly appreciated. I.E. shocks are wear item's and you'd need to replace the shock long before the bushing wore out, etc..
I'm sure the info I’m looking for is sparse as the IRS swap crowd is in the minority. But I’m hoping people can chime in using the rough weight, power, etc. information I have given, if there is more information required please let me know so I can provide it.
Thanks.

[wraithracing]

One thing to keep in mind that as you strengthen the chassis and balance out the suspension on a Fox Mustang your "anti-roll" bar needs will change. The larger bars are needed on stock cars or mildly modified to combat the huge compliance built into the suspension and the body. Install a NASA/SCCA compliant cage and subframe connectors and suddenly the Mustang flexi flyer is no longer quite so mushy! A perfect example of improved handling with a smaller front bar is the OEM 93 Cobra setup. Although I know your setup is far past the capabilities of a stock 93 Cobra, I use that as an example of where the use of a smaller bar allows better handling.

I personally have not seen much in the availability of rear bars for the IRS. I am sure this is for a few reasons, most street drivers don't care, drag racers swap out the IRS for a Solid Axle, and last not that many guys are running the IRS in road racing competition. The bar is simple enough to have a custom bar made if needed, but I would bet that the stock one will be just fine most of the time. Sort out the rest of the car and then see if a different bar is even needed, IMHO.

As for rear coil overs. IMHO, the Bilstein setup from MM is the best option. I am actually about to order a set for my 79 PC with the IRS in back to improve my handling and ride quality on the street. I don't plan to use my PC in competition, but I may use it a bit for some TT or HPDE if the opportunity arises. IMHO, the biggest benefit to a heim joint over a bushing set up is the ability to tolerate mismatched alignment or angle difference. I don't see this being much of issue with the CO in the IRS. I could be mistaken, but from my experience, the alignment is pretty good and I don't see any reason for the heim joint. I am sure you are aware of it, but I will mention it just in case. MM does include a different bushing in the CO kit for the Bilstein IRS application that is a much harder bushing IIRC, than the stock IRS non/CO bushing.

Hope that helps!

Trey

[Mr Joshua]

One thing to keep in mind that as you strengthen the chassis and balance out the suspension on a Fox Mustang your "anti-roll" bar needs will change. The larger bars are needed on stock cars or mildly modified to combat the huge compliance built into the suspension and the body. Install a NASA/SCCA compliant cage and subframe connectors and suddenly the Mustang flexi flyer is no longer quite so mushy! A perfect example of improved handling with a smaller front bar is the OEM 93 Cobra setup. Although I know your setup is far past the capabilities of a stock 93 Cobra, I use that as an example of where the use of a smaller bar allows better handling.

I personally have not seen much in the availability of rear bars for the IRS. I am sure this is for a few reasons, most street drivers don't care, drag racers swap out the IRS for a Solid Axle, and last not that many guys are running the IRS in road racing competition. The bar is simple enough to have a custom bar made if needed, but I would bet that the stock one will be just fine most of the time. Sort out the rest of the car and then see if a different bar is even needed, IMHO.

As for rear coil overs. IMHO, the Bilstein setup from MM is the best option. I am actually about to order a set for my 79 PC with the IRS in back to improve my handling and ride quality on the street. I don't plan to use my PC in competition, but I may use it a bit for some TT or HPDE if the opportunity arises. IMHO, the biggest benefit to a heim joint over a bushing set up is the ability to tolerate mismatched alignment or angle difference. I don't see this being much of issue with the CO in the IRS. I could be mistaken, but from my experience, the alignment is pretty good and I don't see any reason for the heim joint. I am sure you are aware of it, but I will mention it just in case. MM does include a different bushing in the CO kit for the Bilstein IRS application that is a much harder bushing IIRC, than the stock IRS non/CO bushing.

Hope that helps!

Trey

True.
The only one I’d probably trust is the one offered on MM’s website.
http://www.maximummotorsports.com/st...roducts_id=986
I’ve found an Eibach 03/04 rear NIB , so I’m thinking of picking that up as a spare. Powdercoating the stock one, and putting that in with upgraded swaybar bushings from MM for the time being. Till I get the front sorted out and move on to subframe connectors and a cage.
Why the Bilstein’s over the Koni adjustables? I’m also curious if the valving/rebound of the shocks offered by MM with their CO kits would be properly setup for the weight of a fox hatch/coupe. Would the weights be that similar that you could use the stock 03/04 Bilstein’s with MM’s kit(not that I would). It seems that if so the stock 03/04 shocks on a fox would also present the above issue of valving/rebound as well.
If that’s the only reason to use a heim joint in this particular application and the IRS setup has nearly no alignment issue’s with the shocks then I’d tend to think the MM CO kits would work just fine, either Bilstein or Koni when paired w/ this MM kit.
http://www.maximummotorsports.com/st...oducts_id=1089
Also temporarily combining that with a shock tower cross brace until the subframes and cage go in.
I wasn’t aware of that little tidbit of info, thanks.

[wraithracing]

True.
The only one I’d probably trust is the one offered on MM’s website.
http://www.maximummotorsports.com/st...roducts_id=986
I’ve found an Eibach 03/04 rear NIB , so I’m thinking of picking that up as a spare. Powdercoating the stock one, and putting that in with upgraded swaybar bushings from MM for the time being. Till I get the front sorted out and move on to subframe connectors and a cage.
Why the Bilstein’s over the Koni adjustables? I’m also curious if the valving/rebound of the shocks offered by MM with their CO kits would be properly setup for the weight of a fox hatch/coupe. Would the weights be that similar that you could use the stock 03/04 Bilstein’s with MM’s kit(not that I would). It seems that if so the stock 03/04 shocks on a fox would also present the above issue of valving/rebound as well.
If that’s the only reason to use a heim joint in this particular application and the IRS setup has nearly no alignment issue’s with the shocks then I’d tend to think the MM CO kits would work just fine, either Bilstein or Koni when paired w/ this MM kit.
http://www.maximummotorsports.com/st...oducts_id=1089
Also temporarily combining that with a shock tower cross brace until the subframes and cage go in.
I wasn’t aware of that little tidbit of info, thanks.

I forgot about the Eibach unit for the IRS. Sorry!

The main reason I would use the MM Bilstein setup over the Koni is that IMHO MM has more experience and knowledge in setting up the shocks and struts than I do. The Koni are excellent shocks and struts and have excellent adjustablility. Unfortunately I have seen too many people chasing their own problems because of that same adjustability. They began to adjust shocks, springs, etc without realizing what effect that has on other areas of the car. Then when that adjustment doesn't work, they make more, and more, and more and before they know it the car runs worse than ever before and they blame it all on the parts, the car, the track, or anything but themselves. Of course, I have never been guilty of doing such a thing myself! If you have the skills, the knowledge, and the experience on how and where to make the adjustments, then a set of adjustable shocks/struts can be a huge advantage. I don't personally have that . . . yet! Besides there are alot of guys running MM Race spec Bilstein strut/shock setup in AI/AIX and others and are top running guys. I am not going to argue with that for having them setup pretty well.
As for the weight difference between the OEM Cobra and your Fox in the rear, the difference may not be as much as you think. The vert Cobra is definitely heavier in the rear, but most of the extra Cobra weight is up front compared to a Fox. I would check with MM and get their opinion, but I believe you will be just fine with their valving as is.
I do believe the upper shock mounts and a rear shock tower brace makes a great improvement to the Fox too. Overall it's not an expesive option either.

Good Luck!

Trey

[Mr Joshua]

I think after researching all my options, I'll start with the OEM sta-bar and call MM or maybe Jack will chime in on shock recommendations.
I can use that as a base reference and change things in the future, once I have a known starting point.

[85asc239]

I have the mm valved rear bilsteins with coil over on my 98. It rides really well on the street and is very predictable on track. I prefer the ride of bilsteins over konis- also adjusting konis can be pain.

Another great coil over to check out are KW's. Take a look at SVT performance there are a few people that have put them on and loved them.

As far as the rear sway bar goes, if you get the adjustable rear sway links from FTBR you can tighten or losen the bar. A friend raced an 00R in the contental challege and ran the stock rear sway bar.

Hope this helps.


Jeremy

[wraithracing]

I just finished talking to Jack about my PC with the IRS.

His recommendation was either the stock Cobra coupe shocks/struts (essentially same as the MM Sport Bilsteins) with 350lbs/in 2.5" X 10" front springs and 575lbs/in 2.25" X 8" rear springs.

If you use the Cobra convertible struts/shocks (essentially same as the MM HD Bilsteins) the recommendation was 300lbs/in 2.5" X 10" front springs and 500lbs/in 2.25" X 8" rear springs.

Your setup is a bit more hardcore than mine I believe so you would most likely use the Sport setup as a minimum. Which in that case means you might also look at the race valving Bilsteins, but they are generally not recommended for street duty. This will also bump your front springs into the 400-425 range and the rear to 600-650

Send Jack an email. He's a great guy to deal with and very helpful. They stay pretty busy so it may take a day or two for the first response. After that he will get back to you extremely quick. Again can't say enough good things about Maximum Motorsports and or Jack!

Trey

[Jack Hidley]

In a perfect world, both the top and bottom of a shock absorber would be mounted with a spherical bearing. There are two reasons for this.

1) Friction. when the suspension compresses and extends, the angle of the shock changes a little bit on two different axii. It requires some force to deform the bushings at each end of the shock to cause this angle change. This means that a reaction force must also appear between the shock shaft and guide bushing, and the shock piston and cylinder walls. This radial force causes increased friction. Any friction here is bad for ride quality and handling as it keeps the suspension from making small movements.

2) Damping. When the suspension moves up and down very small amounts, if the ends are mounted in a compliant material, it is possible for the piston to never move in the cylinder. The bushings at the top and bottom just deform instead. This means that the shock is not providing any damping. This isn't good for ride or handling.

Any of our rear coilover kits come with an upper mount that is incompressible and has reasonably low friction. Any of these kits can also be mounted with a spherical bearing to get even lower friction.

I'm fairly certain that we can also install a spherical bearing in the lower eyelet of any of these shocks. I'm not sure what the cost or time involved would be.

The main problem with spherical bearings is this. After a certain number of miles, they will develop play in them. How quickly they develop play is a function of the peak loads on them and their size. Once they develop play, they will make very audible noise since they are moving in a 1:1 ratio with the suspension motion here. The upper bearing will last much longer than the lower bearing. The lower bearing is exposed to dirt, water, etc. The vast majority of our street customers, won't accept the life or the noise so we sell almost all of the kits with polyurethane bushings in the lower eyelet and a Delrin/Aluminum ball/socket arrangement at the top.

Having the adjustment on the Koni is an advantage, if you are willing to take the time to adjust it correctly. With the IRS, you are already going to have to deal with all of the rear alignment possibilities. One significant disadvantage of the Konis when used on a track car is that they are a twin tube shock. This means that the oil in them stays hotter, which causes them to loose damping over a track session much more than a mono tube shock (Bilstein). If you run the car at the track near 100% for a full 25 minute session and it is hot out, that can be a problem. The mono tube construction of the Bilstein also allows the use of a larger piston which makes the shock function better at lower suspension displacements.

Step one is to determine what your front suspension will be. Step two is to determine the front and rear tire and wheel sizes. Step three is to figure out how much of a track car versus street car you want it to be. The more track oriented it is, the faster you want it to respond to control inputs. This is the car's transient response. The faster the transient response needed, the higher the spring rates and damping needs to be. Pick the spring rates based on #1, #2 and #3 and then pick the dampers to match the spring rates and car masses.

[Mr Joshua]

Thanks for taking the time to respond Jack!
If I end up going with the MM rear IRS coil overs, (which i am 95% certain I will), I'd be using the spherical upper conversion kit.
I'd wager the time/cost would be great when compared with the actual benefits that I might not even see. To state my uses for this car would be almost all street time, with near 99% of that on sunny warm/hot days which there is a low percentage of those in the North East. The NVH I wouldn't be as concerned with for the above usage reasons.
Are you inferring that the adjustment features and design of the Koni's lead them to be more of a sport shock that when properly tuned that might be more at home on a performance oriented street car than for all out race situation? I'm not sure what you mean by low suspension displacement, could you clarify?
For front suspension, I would like to use a properly setup SLA and it's up in the air between Griggs and Agent 47, both have their pro's and cons. If I run into issues with either of those setups then I would be using a full McPherson coil over setup from MM.
As far as tire sizes, they would be at the bare minimum of 245's on 17 or 18's depending on clearance needed for brake rotor/caliper sizing. This would also change in the future due to the widening of the front and rear fenders to a size not yet determined. More than likely it would be determined by final tire/wheel/brake selection. I feel that the car, even though it's planned use up till this point has been primarily street use, I would like it to respond quickly to it's given inputs. Given my direction over the course of this project, it will more than likely end up at a track in it's future.

[Jack Hidley]

I wasn't trying to imply anything about the Koni's. There are advantages to certain aspects of the Koni design and there are certain advantages to the Bilstein design. The same goes for disadvantages. I'm just trying to point out the pros and cons of each.

That said, the Koni is definitely more oriented towards someone who will use it on track car, since it is adjustable. When used by someone who takes the time to learn to adjust them, this can be a significant benefit. When used by someone who doesn't take the time to learn to adjust them, or worse adjusts them badly, it can result in a car that handles worse than having no adjustment at all. It is a lot like having a carburetor on an engine.

An ideal shock for a track car, is an inverted monotube with double or triple adjustments. This has the better heat dissipation characteristics, with the reduced unsprung weight of an inverted shock and the advantage of damping adjustments at different shock velocities. These are available, but they are very expensive.

By "low suspension displacement", I mean the suspension is only moving up and down a small distance, maybe 0.125"-0.25".

The ratio of front to rear tire/wheel size greatly affects the amount of cornering grip available at each end of the car. This greatly affects the choice of optimum front and rear spring rates, as the spring ratio affects the amount of work that the tires at each end of the car need to do.

[Mr Joshua]

Just clarifying on Koni vs Bilstein.

As I'd expect with any adjustable part in the car, poorly adjusted, car performs poorly.

I've looked at Afco before. I believe they have something that matches an "inverted monotube with double or triple adjustments." It just wouldn't be off the shelf piece, bolt on and go. More custom work to look forward to if i went that route. Also it's one of the only names I've discovered so far. I'm sure there are more, and I just haven't looked hard enough. Something tells me that type of jump should be better left to further down the road where I end up actually needing something of that caliber, and would notice the improvement they make vs a Koni, Bilstein, etc.

I should have thought more about that before asking. Seems so obvious now that I see it in front of my face.

There's no reason I can't start off with 245x45x17 then transition to something larger later on, I'd just have to change out the shocks, springs, etc.. so they'd be matched, correct?

In the end I think that i'd be better off with a Bilstein based coil over setup. Then work my way into the advanced components when I learn more about effectively tuning the components I have.

[Mr Joshua]

I've decided to use MM for the IRS coilovers on my 83 Project. What I need is some assistance in choosing the proper spring rate and shocks for the car. The project specs are in the link in my sig.But here's the basics, stripped 83 mustang GT w/ T-tops, 357W, T-56, IRS, no cage, SS fuel tank. Going to be using it primarily on the street for now.
It appears that MM sells the coilover kit separately from the shocks, as well as Shock eye replacement bushings as well as Racing upper mounts.
I'd like to go with Bilstiens for now.

Shocks & Struts
http://www.maximummotorsports.com/st...ath=514_23_377

Shock eye replacement bushings
http://www.maximummotorsports.com/st...roducts_id=790

Coil Over Kit
http://www.maximummotorsports.com/st...roducts_id=511

Racing Rear Upper Shock Mount, Bilstein
http://www.maximummotorsports.com/st...oducts_id=1089

I'd appreciate any help.

[wraithracing]

The recommendations that Jack with MM gave me for my PC were as follows:

MM Sport struts & shocks and performance handling 350lb/10" x 2.5" front and 575lb/ 8" X 2.25" rear.

Bilstein HD struts & shocks and softer ride 300lb/10" X 2.5" front and 500lb/ 8" X 2.25" rear.

You are running maybe a bit more front weight than I am 302 to 351W. My car is full interior street car, so I might be a bit heavier overall than your car, so keep that in mind. Either way, I think those springs will get you close.

I know Jack will give you a recommendation if you send him an email at MM.

Good Luck!

Trey

[Mr Joshua]

I could call him but I really don't like "bugging" him. If you wanna shoot me a pm w/ his e-mail I'd appreciate it.
I was hoping he'd chime in here so that more people would benefit from his wisdom on the ins and outs for IRS enabled foxbody suspension tech.

[MAD MIKE]

I could call him but I really don't like "bugging" him. If you wanna shoot me a pm w/ his e-mail I'd appreciate it.

If Jack gave you his phone number, use it.

[Mr Joshua]

I'd prefer to have him reply here.

[wraithracing]

PM sent!

Trey

[Jack Hidley]

Joshua,

Assuming equal size front and rear tires/wheels, with the overall weight and distribution your car has, I would use a 600lbs/in x 8" x 2.25" rear spring on an MM Sport valved IRS shock. If you were to use a matching MM front suspension, I would use a 375lbs/in x 10" x 2.50" spring in the front to match. This setup will be quite firm for a street car, and have low body roll for street use. The ride quality will be good on smooth pavement and a bit rough on rough pavement.

The shocks are here:

http://www.maximummotorsports.com/st...roducts_id=787

The coilover kit with springs is here:

http://www.maximummotorsports.com/st...roducts_id=511

The racing rear shock mount is here:

http://www.maximummotorsports.com/st...oducts_id=1089

A couple additional comments about the racing shock mount.

The performance advantage from using it on an IRS car is smaller than if it were installed on a solid axle car. This has to do with the orientation of the lower shock bushing. On an IRS application, the bushing is free to pivot in response to up and down suspension movement with little friction. This produces very little side load in the shock shaft seals. On a solid axle application, the lower shock bushing must compress when the suspension moves up and down. This produces more side load in the shock seals.

To install the racing shock mount, you must drill four holes in the top of the shock tower. If you do need to return the car back to stock form, you will probably need to weld these holes up and grind metal on both sides.

I encourage you to install the coilover kit with the supplied ball and socket upper mount first, and try it. If you don't like it, you can always install the racing upper mount later.

I would use the stock swaybars at first. Get the tires and wheels on the car. Drive it to see what the handling balance is like. Then adjust the handling balance or overall body roll level by changing swaybars. The springs are used to get the overall front to rear ride frequency correct and the overall suspension ride stiffness correct.

[Mr Joshua]

Joshua,

Assuming equal size front and rear tires/wheels, with the overall weight and distribution your car has, I would use a 600lbs/in x 8" x 2.25" rear spring on an MM Sport valved IRS shock. If you were to use a matching MM front suspension, I would use a 375lbs/in x 10" x 2.50" spring in the front to match. This setup will be quite firm for a street car, and have low body roll for street use. The ride quality will be good on smooth pavement and a bit rough on rough pavement.

The shocks are here:

http://www.maximummotorsports.com/st...roducts_id=787

The coilover kit with springs is here:

http://www.maximummotorsports.com/st...roducts_id=511

The racing rear shock mount is here:

http://www.maximummotorsports.com/st...oducts_id=1089

A couple additional comments about the racing shock mount.

The performance advantage from using it on an IRS car is smaller than if it were installed on a solid axle car. This has to do with the orientation of the lower shock bushing. On an IRS application, the bushing is free to pivot in response to up and down suspension movement with little friction. This produces very little side load in the shock shaft seals. On a solid axle application, the lower shock bushing must compress when the suspension moves up and down. This produces more side load in the shock seals.

To install the racing shock mount, you must drill four holes in the top of the shock tower. If you do need to return the car back to stock form, you will probably need to weld these holes up and grind metal on both sides.

I encourage you to install the coilover kit with the supplied ball and socket upper mount first, and try it. If you don't like it, you can always install the racing upper mount later.

I would use the stock swaybars at first. Get the tires and wheels on the car. Drive it to see what the handling balance is like. Then adjust the handling balance or overall body roll level by changing swaybars. The springs are used to get the overall front to rear ride frequency correct and the overall suspension ride stiffness correct.

Thanks for responding Jack, I think that everyone on the forum can benefit from the information you provide.
The car for the time being will be kept with equal size wheels/tires. Eventually a cage/subframes, etc.. But this will give me a good baseline to start with.
Thanks, I wasn't sure if I needed to go with the racing rear shock mount or not.
I figured the answer might be something along those lines as I didn't know how switching to the IRS would affect the shock travel and other aspects of the suspension.

Planning on going with the stock swaybar like you suggested for now, till I get the rear then front end sorted out. I'll keep plugging away on the car till I get where it will most likely end up overall before I start making any real adjustments.
Mainly looking for a better than average starting point/base line then go from there.
Are there any tips that you could suggest when setting the beginning settings of the Coil-Overs? I suppose an install sheet will come with the kit?