IRS swapping my cobra

Tim300wsm · Nov 8, 2022

Hey guys I found a 03 irs for a good enough price that I had to do it. I want to do it right so was hoping for advice and what aftermarket suspension components I should Swap in (autocross/track day) while I have it out. There will be limited street miles so I don’t want to piss blood if I hit a bump but I don’t need a comfortable ride. This will be the biggest project I’ve done so any help is much appreciated

Warhorse Racing · Nov 8, 2022

I've used Full Tilt Boogie Racing IRS upgrades on my two IRS-swapped New Edge Mustangs for several autocross seasons. I highly recommend their parts. I cover those parts and more in these videos:

You might have a hard time finding Tokico D-spec shocks (Koni Yellow SA or DA are good alternatives), and you can use the OEM IRS rear sway bar (with poly bushings) on your car.

white95 · Nov 9, 2022

I’ve toyed with the idea of switching to an IRS. The subject is surprisingly polarizing in the autocross community.

cobrajeff96 · Nov 9, 2022

You need only shop at Kenny Brown for the IRS, however I do recommend FTBR's cross axis joints for the uprights/spindles.

Kenny Brown's subframe, arms, diff brace, and especially his spring/shock options are superior to all else. You can take it from me: I've ran just about every iteration of the SN95's different suspension options, from a Watts Link / Upper Third Link live axle, an IRS with a mix of Maximum Motorsports and/or FTBR components, and now mostly Kenny Brown components with just one or two FTBR / MM parts still in there simply because no one else makes them (MM has the sexy upper shock tower mounts and FTBR has the X-axis joints).

Tim300wsm · Nov 9, 2022

Warhorse Racing said:
I've used Full Tilt Boogie Racing IRS upgrades on my two IRS-swapped New Edge Mustangs for several autocross seasons. I highly recommend their parts. I cover those parts and more in these videos:

You might have a hard time finding Tokico D-spec shocks (Koni Yellow SA or DA are good alternatives), and you can use the OEM IRS rear sway bar (with poly bushings) on your car.

The videos are great. You’re right about the shocks they are OOS everywhere.

Tim300wsm · Nov 9, 2022

white95 said:
I’ve toyed with the idea of switching to an IRS. The subject is surprisingly polarizing in the autocross community.

I wasn’t going to switch but I got a deal good enough to justify it. It seems to have more pros than cons. I want to make sure I do everything right the 1st time so I’m not constantly taking it out and putting it back in.

Tim300wsm · Nov 9, 2022

cobrajeff96 said:
You need only shop at Kenny Brown for the IRS, however I do recommend FTBR's cross axis joints for the uprights/spindles.

Kenny Brown's subframe, arms, diff brace, and especially his spring/shock options are superior to all else. You can take it from me: I've ran just about every iteration of the SN95's different suspension options, from a Watts Link / Upper Third Link live axle, an IRS with a mix of Maximum Motorsports and/or FTBR components, and now mostly Kenny Brown components with just one or two FTBR / MM parts still in there simply because no one else makes them (MM has the sexy upper shock tower mounts and FTBR has the X-axis joints).

The kenny brown stuff definitely looks great but that would blow my budget for the whole project. I need to address the front end and some maintenance/ repair concerns as well

cobrajeff96 · Nov 9, 2022

I hear ya, KB is probably among the more expensive options.

Be sure to invest in a brake flaring/cutting kit, I think I got mine on Amazon real cheap many years ago and I have used it a good number of times. OTC brand, I think. You'll need it for rerouting the one line going to the rear. You'll need a female union, probably M10x1 bubble flare or whatever you prefer to make for the new connection. The factory Y-block on the passenger side will get smashed by the upper control arm if you don't relocate it. So then you'll also need some sort of T-junction to go from one and split it into two for both rear brake calipers. You might also need the 99+ parking brake cables because they are just a bit longer than SRA ones.

To ensure you don't get "Cobra Clunk", don't re-use your OEM forward mounting bolts; instead get the bolts from FTBR. You can either get 14mm or the 9/16" (14.2mm) bolts. Get all delrin bushings because that sounds more your speed. Make sure there's a forward diff brace, either OEM or aftermarket.

You may need to source a custom driveshaft from D&D Performance or somewhere else (really depends on transmission.

Have a big ass pry bar, a flat file, and a sledge hammer. Better yet, those things plus forward torque box spreaders from FTBR.

white95 · Nov 9, 2022

Tim300wsm said:
I wasn’t going to switch but I got a deal good enough to justify it. It seems to have more pros than cons. I want to make sure I do everything right the 1st time so I’m not constantly taking it out and putting it back in.

Cool. I’m just trying to figure this racing stuff out lol

Tim300wsm · Nov 9, 2022

white95 said:
Cool. I’m just trying to figure this racing stuff out lol

Me too and doing it for cheap is damn difficult

Warhorse Racing · Nov 9, 2022

Tim300wsm said:
Me too and doing it for cheap is damn difficult

Focus on driving fundamentals over mods at first. When making mods, always make sure they are solving a problem you can identify. And remember that adjustments are often more important than mods. Eliminating the weak links in an IRS is similar to eliminating the weak links in a stock SN95 Mustang: It's not about spending the most money, it's about spending the right money.

Improving an IRS can be very expensive, but you don't have to change every single component to make it competitive at local autocross events. Both of my IRS cars use the OEM IRS subframe and control arms. They also don't have coil-overs or aftermarket K-members. I'm not the best driver in the world, but my fundamentals are pretty good, and my cars are adjusted to take advantage of the specific mods I've made.

Tim300wsm · Nov 9, 2022

I’m going to start with replacing all the bushings with the full tilt boogie kit and doing the same to the front end. Then subframe connectors and springs/struts. Plus maintenance items like brakes and tires. Nothing crazy next year or 2 just get it sorted before I get to deep in it. I just want to make sure I don’t over look anything it truly needs

Warhorse Racing · Nov 9, 2022

Tim300wsm said:
I’m going to start with replacing all the bushings with the full tilt boogie kit and doing the same to the front end. Then subframe connectors and springs/struts. Plus maintenance items like brakes and tires. Nothing crazy next year or 2 just get it sorted before I get to deep in it. I just want to make sure I don’t over look anything it truly needs

I think that's a good plan. If any other questions come up, please ask. I'm always happy to help.

Tim300wsm · Nov 9, 2022

Warhorse Racing said:
I think that's a good plan. If any other questions come up, please ask. I'm always happy to help.

Did you reinforce the torque box or any other chassis mods when you did yours?

Warhorse Racing · Nov 9, 2022

Tim300wsm said:
Did you reinforce the torque box or any other chassis mods when you did yours?

I use Wild Rides torque box reinforcements and Steeda IRS bracket braces. The rest of the bracing I used isn't specifically because of the IRS swap, it's just a good idea to stiffen these cars up for autocross.

I use the Stifflers FIT System on my 2000 GT and 2004 V6. I also use the Stifflers lower chassis brace on both cars. I use a BBK strut tower brace on my GT and a Steeda strut tower brace on my V6 (I prefer the Steeda one). I also use Steeda rear shock tower braces on both cars (many people think these are unnecessary, but I like them).

I cover the chassis bracing in this video:

Tim300wsm · Nov 10, 2022

Warhorse Racing said:
I use Wild Rides torque box reinforcements and Steeda IRS bracket braces. The rest of the bracing I used isn't specifically because of the IRS swap, it's just a good idea to stiffen these cars up for autocross.

I use the Stifflers FIT System on my 2000 GT and 2004 V6. I also use the Stifflers lower chassis brace on both cars. I use a BBK strut tower brace on my GT and a Steeda strut tower brace on my V6 (I prefer the Steeda one). I also use Steeda rear shock tower braces on both cars (many people think these are unnecessary, but I like them).

I cover the chassis bracing in this video:

Thank you. I want to do all I can while the rear end is out. Make things much easier