Has anyone used a Cobra IRS in a '33?

[progmgr1]

All the discussions I've seen are about solid rear axles and 3 or 4 link suspensions. Is it possible / easy / desirable to use the Ford IRS instead? I'm still in the planning stages, so this is just a dumb question from a newbie. Thanks for your insights.
Keith

[myjones]

All the discussions I've seen are about solid rear axles and 3 or 4 link suspensions. Is it possible / easy / desirable to use the Ford IRS instead? I'm still in the planning stages, so this is just a dumb question from a newbie. Thanks for your insights.
Keith

Keith
Possible yes, easy not so much, desirable, depends on your intended use vs budget for the build.
There are a few out there already and at least one vendor working on a bolt in set-up to be released later.
I chose an improved 4 link to eliminate bind and softer springs, different shocks and added sways all for a more street friendly ride.
Dale Berry
Hemi 33

[progmgr1]

Thanks Dale.
I understood from other threads that the 3 link version was more street friendly than the 4 link. Why did you pick the 4 link and what was "improved" about it?
Keith

[myjones]

Thanks Dale.
I understood from other threads that the 3 link version was more street friendly than the 4 link. Why did you pick the 4 link and what was "improved" about it?
Keith

The 3 link bracket takes up trunk space and has been wadded up by 33's with much less HP than I will have. It and the panhard also takes up space I needed for my re-located gas tank. The 4 link as delivered uses links with no pivots so it binds fairly quickly. I had custom, adjustable links made with heim joint ends and a sway tab on the lowers. They let me adjust the wheelbase and pinion angle fairly quickly and they don't bind. I also added bumpstops and limit straps to work with the softer springs and adjustable shocks I chose. The kit as delivered is a track car that can be street driven, I wanted to reverse that scenario.
Dale
Hemi 33

[progmgr1]

Thanks again Dale. Your solution makes a lot of sense and sounds very slick. Do you have a photo available to post?
I'm really glad that you folks on the forums are so willing to share your experience. Hopefully I will keep out of trouble if I pay attention.
Keith

[myjones]

Thanks again Dale. Your solution makes a lot of sense and sounds very slick. Do you have a photo available to post?
I'm really glad that you folks on the forums are so willing to share your experience. Hopefully I will keep out of trouble if I pay attention.
Keith

Keith
Just got the chassis back from paint and starting to assemble everything so no fully assembled pictures yet but;
I have some various pics in the Gallery here from mock-ups just look under myjones and on the other forum look under Buck70
The cool thing about the 33 is how many different ways they get built based on what the owner wants to take on.
Dale
Hemi33

[Tim Whittaker]

I'm using the 8.8 like the Cobra. Both Cobras I built had the IRS and I like it so much, the plan from the beginning was to use an IRS on the 33. I have it about half done and plan to have the IRS install done in a few weeks.

I'm making jigs as I go to make a bolt in kit available.

Dan Ruth has also done a couple of IRS 33 builds

[In33anity]

Keith,
Long before deciding to run the full BMW e9x M3 drivetrain, I settled on it's five link full IRS. As I saw it, was super cost effective and a relatively straightforward install. The cobra IRS is already a weld-in with a heavy amount of modification, costs about $2,200 for the FF kit, the FF Wilwood 12.19" brake package is another $700, add in the cost of a decent shape crown and all the other bits and you're up over $4,000 and probably closer to $4,500. And, it's all based upon a late '80's or early '90's Thunderbird/Lincoln differential that was not designed for the type of performance I was looking for. Comparatively, the M3 rear is well proven at 200 mph performance, the car is rated OEM at 175 top speed (with the ECU limiter in place) and has been really robust in racing applications, with Goiken and other aftermarket companies making crazy LSD's if you really want to push it to the outer limits. The advantage of BMW's 5-link is the wheels are always moving straight up and down with zero change in angle. It comes as a complete drop-out attached to it's own subframe that attaches with four bolts in the corners on two parallel planes that seemed comparatively straightforward to design around. The M3 and the FF '33 share the identical 62" track width so it fits straight up. Comes with OEM brakes at 14.2" compared to the 12.19" Wilwood's and can be had with either a 3.15 or 3.86 (what I'm running) ratio. When I asked The Driveshaft Shop who is making my shaft about switching out the axle half shafts for my 700+ HP application they said don't bother as the OEM is strong as can be and can take it. The Backdraft Cobra runs the earlier version (E46) of the M3 IRS also bolting in the complete subframe and the reviews on it's handling are really high. The one person I spoke to who said they've driven both the Backdraft and the FF Cobra's with IRS said there was no comparison in the handling. Typical cost for a relatively low mileage e9x M3 IRS with brakes complete from hub to hub is $3,000 or a little less. The E46 version is cheaper still. Like Dale, I also moved the fuel tank (and in so doing switched to a cell) to improve the center of gravity and open up some trunk space, but with the fixed shaft afforded by the IRS and no room needed for the links, it allowed me to drop it straight down. The one change I have made is to switch from a spring and strut to a true coilover. I've added a set of off road towers to keep the tops from shearing off, which has been known to happen with true coilovers in the OEM body without reinforcement on this IRS. -- I

[Tim Whittaker]

My IRS is a bolt in unit. I wanted to offer something for those that don't have the welding skills to make this mod.

Although it truly bolts in, there are some minor modifications to the trunk sheet metal.

[myjones]

Keith,
Like Dale, I also moved the fuel tank (and in so doing switched to a cell) to improve the center of gravity and open up some trunk space, -- I

I
Nice pictures, love to watch the fab work you do. I noticed you still have the tabs for the big hoop trunk hinges on yours and I wanted to suggest another way to keep trunk space and get a better overall result. The 03 and up Mazda 6 uses a small compound action trunk hinge that also has integral lift supports. I saw them on an American Steel body and plan to use them on mine. The lift supports and losing the big space robbing hoops is a win win.
Sorry for the thread jack but it goes with the picture above.
Dale

[In33anity]

I
Nice pictures, love to watch the fab work you do. I noticed you still have the tabs for the big hoop trunk hinges on yours and I wanted to suggest another way to keep trunk space and get a better overall result. The 03 and up Mazda 6 uses a small compound action trunk hinge that also has integral lift supports. I saw them on an American Steel body and plan to use them on mine. The lift supports and losing the big space robbing hoops is a win win.
Sorry for the thread jack but it goes with the picture above.
Dale

Dale,
Love the idea. I hate the hoops and the cross-bar, but hadn't come up with anything better. My crossbar is actually removable and slides into the two upright sockets so I could drop the gas tank straight down as it was too wide to slide in past the rollbar brackets. Calling my guy at Nationwide, my yard of choice first thing in the am to get him on it. Mutual watching your fab work too--like the sideboard supports! Thanks!!!