GTs with IRS, a community?

[secondchance]

I recently completed the Solid to IRS swap on my 40th Anniversary Special convertible. Basically, I got tired of the car feeling like a pickup truck just after a bump or pothole. Things would get more exciting if that pothole was in a turn. Modern cars should have independent suspensions.

I thought I would post a note to see how many other folks have done this conversion.

I would like to hear from you about your motivation for making this change, whether you did the work yourself or had it done professionally, tips and pitfalls and how you like the result. I'm sure there will be comments that someone must be nuts to do this, perhaps, but comments, preferably constructive, are welcome. So let me know who you are. I'll be happy to hear from you. Or maybe there is already a site for this?


My wife and I did the work ourselves in our garage. We installed a low mileage IRS from and '04 Cobra that got from MPS. Other bits included an MM Cobra upgrade kit for both ends that we bought through StangSuspensions. Josh Sadowsky suggested the H&R sport springs, Bilsteins and MM CC plates. These worked out great. An aluminum driveshaft from the DriveShaft Shop connects the IRS to the auto trans. I got a temporary scrap Cobra exhaust from MPS but will replace it in the Spring.

So far I am very pleased with the result. The car is much better behaved over rough pavement. The ride is a bit stiffer as you might imagine and the handling is significantly improved.

The only surprise was that the H&R sports didn't lower the front of the car (1")as much as the back (1.5"). My guess is that this is due to the difference in the front end weight between the Cobra and the GT. It still looks good.

There are a few folks who helped immensely, Jerry Brewer's page

http://www.stangpro.com/html/articles/irs.htm

was particularly useful. The only thing I might add is to remember to remove the pinion snubber before installing the IRS and that the front IRS attach points must bolt up first.

Regards,
secondChance

 

[BCB00GT]

I installed my IRS about 2 weeks ago. Did it myself with the help of my buddy in my garage. Much better handling on bumps in the turns.

No real problems with the install, though I had the wrong rotors. I seem to have a small noise from the left side that I haven't determined what it is. Low thud type sound non metal.

You are right, install front and then lift rear up to bolt in.

 

[Superhereaux]

my 'o2 is my dd and i'd LOVE to have IRS, one just hasn't come around yet

 

[forum155pl]

i keep putting ads in craigs list to trade someone for my 31 spline 410 rear but nobody has called me on it.. i agee.. IRS is the ****.. if anyone knows of someone in the north west give me a PM..

I hope you guys dont see this as a classified

 

[02LaserRed2V]

I've driven terminators quite often and I really don't see what's so great about the IRS. It does make going over railroad crossing a bit smoother but other than that I see it as extra weight.

 

[gsjohnson]

I think it all depends on your end preference. For a daily driver, I would much prefer the IRS. But if your a drag racer, going to the track now and then, then IRS is not for you. If your a Road Racer, then you could go either way. Both can be made to handle quite well.

 

[Blinkstang]

I also have an 03' IRS in my 02' GT. Second best mod I've ever done to my car besides the blower. Everyone told me I was crazy for getting rid of my solid after having just installed the blower a few months prior. But I am not a track whore, I'd rather have a better feeling car driving on city streets in Chicago. I remember not feeling much of a difference after the swap. Then a few days later I gave it some gas thru a curve I always pass near my house - the car hugged the contours of the road and the rearend actually went where I wanted, instead of sideways in my rearview mirror. After that I was hooked, haha.

I always thought about doing an IRS conversion for my car, but wasn't sure if its what I really wanted/needed. Then one day while browsing the classifieds on another forum I happened to find a deal I could not pass up. Found a guy with an 03' Cobra who was local who wanted to swap straight up. I had been offered a swap before, but had turned it down since it was the older 99/01' unit. The guy I swapped with was in the process of installing a THP twin 57mm turbo kit with a VT 302 stroker - so he wanted to do away with the IRS and build up a solid.

On top of not having to pay anything extra, seeing as it was a straight swap (my solid for his IRS) - he also let me keep all the aftermarket upgrades I had on my rear end - which consisted of my Tokico Shocks, almost new MAC Catback, and my H&R Springs. He was upgrading everything and did not need any of the parts! The only thing left on my solid that was aftermarket were my 4.10's. I was actually happy to swap to 3.55 gears since I wanted more room to wind out my Heaton. I sold the solid pieces he let me keep and used the money to buy a new IRS Mac catback and some Kenny Brown springs for the rear.

He gave me everything on the IRS unit rotor to rotor, including brake lines, parking brake cable, Bilstein's, everything.

I drove my car to the shop where he had his car, and we swapped in the IRS over the morning/afternoon - got there at around 8-9am and was driving to a meet back in Chicago around 4-5pm, haha. We just set my solid to the side since his car was in pieces with no motor, etc... This was back in May. He just recently finished his car and finally got the new motor and setup buttoned up.

I have had no regrets swapping to an IRS, and find it to be much more fun when driving - car feels a lot more controllable. I'd do it again without a second thought! Haven't had a single problem since the swap, no noises, vibrations, etc... Feels just like stock.

Next spring I plan on converting the Bilstein's to coilovers with MM's kit, along with a BilletFlow IRS Brace, and some subframe bushings. I also have the low profile bolts and some spacers waiting to go on, so I can finally mount my 315's that I've had sitting in my garage forever. I also want to modify my current catback. The exhaust pipes on the MAC IRS Catback do not hang perfectly horizontal like you are use to seeing when looking at a Cobras rearend. The exhaust pipes actually slope up on each side. I want to pickup a Magnaflow or Borla catback and have my MAC mufflers welded in, as I love my current exhaust setup (I'm on my 4-5th setup).

Here's a rearend shot of my junk box from over the summer, you can see how the MAC catback is special ed and slants upwards.

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Well thats my IRS story, sorry for the long read, haha.

 

[thomas91169]

streets around here suck, so IRS will be staying in this Terminator thats for damn sure. i hated the skip/whiplash feeling from my 02 GT everytime i hit the smallest hole or bump in the road. of course, im more into turning than just racing in a straight line, so IRS helps in that as well.

 

[secondchance]

Thanks everyone for your replies and pix, happy stories and constructive comments. Hopefully we will hear from others.

I added an old picture to my sig. The Cobra is mine but the black GT is my wife's. I'll add a picture of the crimson GT-IRS when the weather here improves.

I'm undecided about what to do with the stock rear wheel/tires, they get lost in the wheelwells. This is made more apparent by the lowered stance with the H&R springs. I'm considering 18x10 wheels and 295s but I can't get these in the Arizona beige stock color that is a part of the 40th Anniv. package. The theme for this car is the 40th Anniversary Special Ford could/should have built so I'm trying to keep the good bits. Spacers may help the appearance from the side but may look strange with the stock 245's from the rear.

 

[BennyBlown2v]

Here goes my story

I started with suspension mods on my car from the beginning. I always felt like the car had a relatively good feel stock, but could be greatly improved by stiffer springs and more aggressive dampers. I originally switched my setup to bolt-on stuff, tokico HP shocks/struts, Pro-Kit springs...but that wasn't enough! I decided coilovers would be next for the front (and I did them right away), then started searching for an 03/04 IRS to swap in. I guess my main reason for wanting an IRS was driving 03/04 cobras and 99/01 cobras before settling on my GT (I was 17 when I bought the car and couldn't afford the insurance on one of the "big boys" lol). For the IRS I skipped bolt ons and went straight to a Maximum Motorsports set of coilovers, diff/subframe bushings, etc.

I had the car with IRS and coilovers all around for about three months during the winter before I added the blower (so I probably drove it 3-4 times during those months haha). Come spring of that year I immediately started drag racing (this was the year I turned 18 so I could go to the track without a parent, hah), cutting 1.9 60's on 245 street tires, and later low 1.7's on MT et street radials....all with an auto-x/street tuned setup I started Auto X'ing but could only get out a couple times due to scheduling, etc...and at the time open tracking (HPDEs) was too expensive for me...so I guess I started to want more launch at the strip as I could go there once if not twice a week!

....long story short I got used to those 60's and wanted 1.5's...so I swapped BACK to a built solid axle

Big mistake! The car didn't feel the same, felt WAY to light in the rear, and the balance was far far off. This past winter '06 I swapped back to an IRS with the same setup as I had before, plus a billetflow IRS brace to keep the diff cover from cracking I always have the urge to pickup a modified cradle and tubular arms, adjustable sway bar links, tie rods, lvl 5 halfshafts, etc etc etc... But currently I'm in a place where I just want to grab a set of NT01's and hit the road course - keeping power and suspension setup basically the same (as in no new parts, just tuning and adjustment).

 

[thomas91169]

werd. i dont have any times, but i used to get outlaunched to hell and back against my buddies 06 WRX in my GT, now i usually stick with him all the way through first. love how the IRS just squats when you get on it. i thought launching with 450tq @ 2000rpm would be harder than a GT which can barely make 300tq, but dam i was suprised the first time i left the stop sign under full power, it just squatted and stuck. i also have (or had) a 1g awd dsm and i dont even think that car could hang launching against my car.

 

[LaserSVT]

Quick question, is there a difference between 99/01 IRS and 03/04?

 

[Blinkstang]

Quick question, is there a difference between 99/01 IRS and 03/04?

Yes - LINK

 

[Bad92GT]

I've just never been a huge fan of IRS... a maximum motorsports torque arm, LCA's, and panhard bar pretty much takes out any of that slack solid axle bad handling/feeling you get from bumps and curves.. I figure if a solid axle has been working all these years in mustangs and it's still going, theres not a whole lot you can do to make it better.

 

[gsjohnson]

I've just never been a huge fan of IRS... a maximum motorsports torque arm, LCA's, and panhard bar pretty much takes out any of that slack solid axle bad handling/feeling you get from bumps and curves.. I figure if a solid axle has been working all these years in mustangs and it's still going, theres not a whole lot you can do to make it better.

There is nothing like the ride of IRS. The comfort level and the way it absorbs bumps and uneven roads cannot be matched by a live axle.

 

[02LaserRed2V]

To each his own. Everyone has their own preference. I for one see nothing that great about the IRS except it's a little more comfortable on crappy roads. But a buddy of mine with a KB 2.8H 03 Cobra swears by his. And even though he recently popped his level 5 half shafts on the very first launch at the track, he still stands by it and refuse to swap for SRA.

 

[Bad92GT]

There is nothing like the ride of IRS. The comfort level and the way it absorbs bumps and uneven roads cannot be matched by a live axle.

I've driven 99+ cobras before.. cornered and beat on.. and the difference between my car and that car was not a whole hell of alot.. not enough to justify a whole damn new rear end for me lol the maximum motorsports rear setup for a solid axle is unbeatable to me.. it's basically changed to a 3 link and kicks more ass then chuck norris on speed

 

[BennyBlown2v]

I've driven 99+ cobras before.. cornered and beat on.. and the difference between my car and that car was not a whole hell of alot.. not enough to justify a whole damn new rear end for me lol the maximum motorsports rear setup for a solid axle is unbeatable to me.. it's basically changed to a 3 link and kicks more ass then chuck norris on speed

Both have their place in road race and street applications. Talking to the guys at MM they really push for IRS stuff and are strong believers in its capabilities when properly equipped. IMO, and pretty extensive personal experience with both, the IRS is a more versatile and more appropriate setup for a street driven car that see's a little bit of everything. And really, the ride quality on an IRS is much better; you must be driving on great roads, or have a quite a bit of meat on your bones (jk ), if you can't a huge difference

 

[TheBocSez]

Although I did not do the install myself, I bought a 00 GT with a 01 IRS already installed. I understand that it is not as good as the 03/04 per se, but I like it. It is a smoother ride but its still no Caddilac.

I also have a lot of slack in the drivetrain with it and get a noticable thump when shifting if its not RPM matched.

I have a complete set of poly bushings and brace to install when I go to install my gears. I have thought about going back to a SRA to get rid of the thud but who knows.

Regarding the springs, the guy that installed it, put H&R race springs on the car, using GT springs up front and Cobra springs out back. The car has a perfectly level lowered stance and looks really nice.

 

[secondchance]

I struggled perhaps a little too much while deciding whether to upgrade the solid or swap in the IRS. The bottom line for me turned out to be ride quality. A buddy of mine had a GT with a solid setup that seemed quite harsh so I went with the IRS. The added weight, about 70 lbs. is in the back so it helps balance but is still added weight. I don’t know how much weight the solid setups add. The IRS reduces unsprung weight by about 125 lbs. so compliance is improved. The cost of the IRS conversion was a bit higher.

I’m getting a bit off topic here but Ford will continue to put the solid in the Mustang as long as they can get away with it. I don’t blame them, they are making a bundle ( and they need it). This may change after the Camaro comes out, depends on the price. Maybe they can offer the solid as a drag pack option.