[stephen_wilson]

You dont get much better than a Miata for handling for under $50,000...they handle far better than a Cobra or Mark VIII because of the suspension design...

That's a bit of a simplistic view, don't forget the not-insignificant fact that they are probably 1,000 Pounds lighter !

 

[Garth66]

Interesting idea... I look forward to more updates.

LOTS of information here about a friend of mine who swapped a Toyota Supra IRS into his 65 Mustang - The Suprang!
Sean's Suprang Page

 

[Tom65]

I wouldn't hesitate to buy a muscle car that has been improved with parts that work better. Then again, I am not into the whole toxic masculinity thing most "car guys" seem to buy into. My masculinity speaks for itself, the suspension in my Mustang doesn't have to do it for me.[/QUOTE]


great information. thanks for sharing

 

[andrewb70]

I have a few things to add, since around 2005-2010 I was playing around with second gen (FC) RX7s (LS swapped) and was the first guy to offer a kit to swap in a Cobra diff into the FCs. It was used in this car and may still hold the FC IRS record:

What does this have to do with a Miata, you might ask. The fun fact is that the FC and the NA-NB Miatas used the same differential mounting points to hang the diff from the chassis. This is the part that is missing from the diagram shown on the first page.

Both the Miata and the FC have two giants (16mm I think) studs that are welded into the frame structure that the diff mounts to. The front diff support is very different between the FC and the Miatas. The FC used a large rear crossmember and used a trailing arm set-up much like the ones found on 944 Porsches (the Japanese have always been great at taking existing designs and making them better). The Miatas had the cradle that was pictures and used a superior double A-arm arrangement.

I think this is all doable, however, I don't think it will be easy or cheap. When I did the FC parts, I worked with Frank at The Driveshaft Shop for all the work on the hubs and stub axles. He may even have billet options already available, but again, not cheap.

At the end of the day, I guess I would want to know what problem you are trying to solve and why you think a IRS system would do it for you. If it's just a since project, I totally get that.

Andrew

P.S. I was living in BGKY at the time and the cradles were made in Franklin TN at a shop called Earl Owen's fabrication. Wonder if old Earl is still around. Getting old sucks.

 

[cobra94svt]

The Cobra IRS is basically a narrower version of the Lincoln Mk VIII/ TBird IRS. There is no practical way to shorten the wide cast-metal LCAs. The most successful TBird IRS swaps have been to full-size pickups.

I put an 03 cobra IRS in my 89 fox notch. I mini tubbed that car and made tubular upper and lower A arms that were 3” shorter, heim joints, shorter shafts, and coil overs. I’m not an engineer but it drove great, and could get 18x11 wheels and 335 tires in the back. I had used off the shelf a arms that were cut to length and weld your own joints on. They were circle track stuff. Then I welded on new ends to mount the hub assembly. The shafts were pricey, a lot of IRS parts from full tilt boogie racing, Kenny Brown.


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[cougar70]

I put an 03 cobra IRS in my 89 fox notch. I mini tubbed that car and made tubular upper and lower A arms that were 3” shorter, heim joints, shorter shafts, and coil overs. I’m not an engineer but it drove great, and could get 18x11 wheels and 335 tires in the back. I had used off the shelf a arms that were cut to length and weld your own joints on. They were circle track stuff. Then I welded on new ends to mount the hub assembly. The shafts were pricey, a lot of IRS parts from full tilt boogie racing, Kenny Brown.


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I was saying that there is no practical way to modify the TBird rear suspension. I suppose it is possible to shorten and weld. The lower control arms in both cars are quite heavy and large due to the spring seat. I'm surprised you had to narrow the Cobra so much. Would the Cobra rear fit under a classic Mustang with smaller wheels and tires?

 

[cobra94svt]

The cobra rear uses the same big cast arms and spring pockets too. It would fit a Fox with 8” wide wheels but that’s no fun lol. As far a vintage car, I’m not sure.


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[j persons]

The MK2 and MK 3 FFR Cobras use a TBird IRS along with custom shortened axles and fabricated upper/lower control arms. The MK 4, I think uses a Mustang IRS with fabricated control arms and corresponding axles. I see no reason why this couldn't be applied to an Early Mustang.
Here's the MK 4 IRS assembly
https://www.factoryfive.com/galleries/mk4/independent-rear-suspension/

 

[Fishfreq]

Its been forever since I posted on here(sold my one project car, but about to buy another 66 coupe next week). Anyway, in the time since I sold my last mustang I bought a 91 Miata I drove for a few months...and they of course handle extremely well...but more importantly the whole IRS system is based on a cradle that bolts to the chassis with 4 bolts...the control arms(upper and lower), carrier, etc. Obviously the miata carrier isn't sufficient for a torquey v8 or even a built inline 6, but the cradles are easily modified to hold a Ford 8.8 IRS from a T-bird or Explorer, or Cobra(I actually have a Ford 8.8 mounted to a spare miata rear cradle right now). With the Miata track width being 56.2" and the 65-66 Mustang being 56" it makes it a very appealing option. Miata hubs can be swapped for T-bird/Cobra hubs with minimal modification(though the 5 lug bolt pattern on the T-bird hubs needs to be redrilled to 5x4.5, whereas the far more expensive Cobra hubs already have the right pattern).

The only real problem I see(aside from cutting down an re-splining whatever CV axles best fits the carrier/hub combo you choose(Moser does this for a little over $100 an axle if I remember correctly)) is the physical fitment of the cradle in a mustang chassis(mostly shock mounting and whether the thing will fit in the space meant for a solid axle). Anyway, purely theoretical discussion...practical option? maybe with a shorter strut assembly?

Sounds like a great idea wicked93gs, and seeing that you have a spare miata cradle there, you're set to try this! From your picture it looks like the 4 mounting bolts are on top, correct, where it looks like they are on a flat plane? The underside of our vm's looks kinda rounded. Doesn't look like a HUGE fab issue, fairly basic. The miata cradle looks like fairly light-weight stamped and formed steel, so adding that weight to the substructure of a vm is probably a wash vs the leaf springs and full axle you take out? How much does your cradle assembly weigh?

If you fab, you might also think of jigging up a tubular replacement cradle like the Original Venice Crew did with their Shelby IRS that matches the miata upper and lower ca's and bolts right into our vm's for a stronger and solid connection? If this whole think could be made a 'kit' using lots of readily available jy and aftermarket miata and ford 8.8 parts, I don't see why it couldn't be done for a fraction of the cost of an OVC or Heidt's IRS kit? Pipe dreaming here too...

Yours looks a bit lighter weight than the Jag IRS parts that I've seen. Weigh that cradle for starters.

https://www.heidts.com/part/64-70-mustang-irs-independent-rear-suspension-racing-kit

 

[Fishfreq]

The Miata spring pockets are actually on the outside of the frame rail(see attachment I grabbed from GRM). Its hard to say whether you would be able to duplicate the setup on a vintage mustang. I would really need to measure the frame rail spacing on both cars to see where the upper shock mount would have to end up(I suspect the frame rail spacing is wider on the mustang by about 5-6" which would require mounting inside the frame rails and likely coilover shocks strictly for the smaller diameter spring) In any case, it is something I plan to look further into because it really doesn't seem to difficult...at worst it would require some floor cutting/reshaping for clearance and some new spring pockets/rear shock "towers" welded in, as well as some type of frame to hang the cradle...all pretty simple fabrication.

If there's not enough room for the coilovers and pockets under our vm's, you could use some sort of push-rod setup with the shocks horizontally mounted in the trunk via rockers, like Mike Maier's Ol' Blue? Always loved the look of that setup and would gladly give up some trunk space for that, and maybe the trunk shock mount could bolt thru to the miata cradle top mounts to stiffen up the entire vm's rear structure? I know, this would start pushing the cost up closer to those full IRS kits, but just sayin'. MM sells the 'diy rocker' kit starting at $1,500 plus options...

 

[elcam84]

Intersting idea. Now I have a 66 in the shop on jack stands with no rear suspension and no front either... I have a neignbor across the street thats a miata guy and has all the suspension parts from a Miata he parted out....