With the exception of the tubular K member that is the same essential suspension that is on both my 79 Pace Car and now my 86 GT. Ride quality is improved if the shocks and springs are matched properly. If not, honestly not much difference in my experience. The biggest issue with the IRS is the MUCH WIDER width of the rear suspension. Wheel fitment becomes an issue and you generally have to run much deeper offset wheels. I run a 36mm offset on 17x9 Cobra R's on my Pace Car and they work, but honestly for a bit more wheel lip clearance I would like at least a 40mm offset. My 86 GT is getting flared rear quarter panels to match my Maier Racing front flared fenders, so wheel offset and sizing doesn't apply here.
To make the change you will have to do some brake line work in the rear, (I recommend the Maximum Motorsport kit), you will want the 94/95 Cobra brake M/C and (again the MM brake line kit helps), make sure the CC plates your buddy has are 79-89 style and not the 90-93 style as they are not interchangeable. You will need the rear exhaust hangers for the 99-04 cars to fit the IRS exhaust (Pypes mounts from LMR are the least expensive option). If the Bullitt wheels are the standard 8" wide with 30mm offset they will work in most cases and should be fine if you don't want wider wheels or tires.
The IRS will hold up to drag racing if you don't get completely crazy. Honestly the full bushing kit from either Maximum Motorsports or Full Tilt Boogie Racing is the way to go. HUGE Improvement in the overall handling, ride, etc. of the IRS. Not a cheap option, but well worth it. Urethane or Delrin subframe bushings should be the bare minimum to start with. The rear subframe mounts are somewhat of a PITA to mount correctly, but can be done on a Fox, check out my 86 build thread for one option.
http://vb.foureyedpride.com/showthre...r-Street-Build The Steeda or BilletFlow rear cover brace is mandatory for drag racing and really should be on all Cobra IRS. Truthfully the front and rear differential bushings should be swapped for urethane or delrin (MM or FTBR again). The pinion drive shaft flange is different on the IRS if your buddy hasn't swapped it already to the Fox sized, so keep that in mind. Front subframe (lower control arm) on the body bolts were 12mm on Fox and generally the 03/04 Cobra used 14mm, so keep that in mind when ordering bushings and which bolts you are using as the sleeves are different and if using the 14mm bolts you have to drill out the holes on the body.
Depending on the deal from your buddy it sounds like a no brainer to make the swap. It's not exactly a bolt in, but reasonably close. So if you have the tools and skills to make the swap its just time consuming. Definitely changes the whole characteristics of a Fox and can be a lot of fun to drive. Hope that helps and good luck!
Connect With Us