IRS upgrade

[BrewCityCobra]

So I'v been looking into build specifics/budget for a future Cobra build and was wondering - is it possible to upgrade to IRS after the fact (e.g., after the car has been completed)?

Right now it looks like the financial hit for IRS is just a bit too far out of my league to include IRS in the initial build and straight axle is the way I am leaning. With that said, I always like to know what doors I'm closing that can't be opened at a later date.

I wasn't sure if the frame itself is made differently to accept IRS or if was something you can always bolt on later (even though I suspect it would be very difficult).

Any insight is always appreciated.

-Brew

[edwardb]

The frame is significantly different with IRS. Officially there's no upgrade possible. I read about one that Factory Five did for a track car a few years ago. Don't remember the specific details. Also I've seen at least one forum member that made the conversion. Involves a bunch of cutting, welding, etc. in addition to the different parts from Factory Five. For sure it's not a bolt on. Don't know what your skill level or interest would be to go that deep. Not for me, that's for sure.

I don't know what you're thinking of using for a solid axle if you went that way. Can range anywhere from a few hundred for salvage (plus likely some rehab expense) to a $2700 for the Moser listed on the order sheet. And whatever you did have wouldn't be used for IRS. How about this? Look at salvage for the IRS pumpkin and knuckles/hubs. They're plentiful and if you're not super picky could find them for pretty cheap. Knuckles would be one and done. Bearings bolt in so worst case those can be replaced and they're not particularly expensive. The pumpkin could be swapped out with something more to your liking and/or better in the future, rather than doing a full IRS conversion. In that scenario, I'll bet the price difference is less than you think. I've had both (solid and IRS) and IMO it's worth pursuing.

[CraigS]

I did the 2015 IRS upgrade 3 yrs ago on my old MkII. It was a lot of work, a lot of welding so you need to be good at that. Especially at welding in awkward positions. I did Tig but I think mig could work also. So it can be done but I agree w/ EdwardB be careful at the $ comparison. I bought a salvage rear suspension and was sure it included brakes. I got a 315 diff because I couldn't find a 331 but that helped because that is not popular so I think that dropped the price. The brakes are excellent. I have no thoughts of upgrading at all. So I think FFRs upgrade is about $2400, and the salvage stuff is $1000 so $3400 does it. There is no question in my mind that the IRS is a worthwhile upgrade. And although no one wants to think about it, the IRS would be well worth having when it's time to sell. If I were looking to buy a used FFR, I wouldn't even look at a solid axle car.

[BrewCityCobra]

The frame is significantly different with IRS. Officially there's no upgrade possible. I read about one that Factory Five did for a track car a few years ago. Don't remember the specific details. Also I've seen at least one forum member that made the conversion. Involves a bunch of cutting, welding, etc. in addition to the different parts from Factory Five. For sure it's not a bolt on. Don't know what your skill level or interest would be to go that deep. Not for me, that's for sure.

I don't know what you're thinking of using for a solid axle if you went that way. Can range anywhere from a few hundred for salvage (plus likely some rehab expense) to a $2700 for the Moser listed on the order sheet. And whatever you did have wouldn't be used for IRS. How about this? Look at salvage for the IRS pumpkin and knuckles/hubs. They're plentiful and if you're not super picky could find them for pretty cheap. Knuckles would be one and done. Bearings bolt in so worst case those can be replaced and they're not particularly expensive. The pumpkin could be swapped out with something more to your liking and/or better in the future, rather than doing a full IRS conversion. In that scenario, I'll bet the price difference is less than you think. I've had both (solid and IRS) and IMO it's worth pursuing.

Sounds like that is a "no" for me then......lol. I can weld but never to the point where I would trust the entire rear end on it. In the end, sounds like this is a decision that will need to be made before I order the kit (Back to the Budget Spreadsheet!).

Originally, IRS wasn't really on my radar but the more I've read about it the more I think it may be worth including. Better ride and I'm hoping to AutoCross/Track the car once it gets complete. From what I have read it really improves handling as well.

[BrewCityCobra]

I did the 2015 IRS upgrade 3 yrs ago on my old MkII. It was a lot of work, a lot of welding so you need to be good at that. Especially at welding in awkward positions. I did Tig but I think mig could work also. So it can be done but I agree w/ EdwardB be careful at the $ comparison. I bought a salvage rear suspension and was sure it included brakes. I got a 315 diff because I couldn't find a 331 but that helped because that is not popular so I think that dropped the price. The brakes are excellent. I have no thoughts of upgrading at all. So I think FFRs upgrade is about $2400, and the salvage stuff is $1000 so $3400 does it. There is no question in my mind that the IRS is a worthwhile upgrade. And although no one wants to think about it, the IRS would be well worth having when it's time to sell. If I were looking to buy a used FFR, I wouldn't even look at a solid axle car.

It's funny you bring up brakes because that is what I'm looking at as a potential compromise. Get IRS with the initial build (instead of Wilwoods) and hold out hope for upgrading the brakes sometime in the future.

Any thoughts?

Daily driving is the primary concern with the car (hoping to get a few road trips in) but the car will definitely be called upon for a few autocross/track days every year as well.

[caesarmascetti]

So I'v been looking into build specifics/budget for a future Cobra build and was wondering - is it possible to upgrade to IRS after the fact (e.g., after the car has been completed)?

Right now it looks like the financial hit for IRS is just a bit too far out of my league to include IRS in the initial build and straight axle is the way I am leaning. With that said, I always like to know what doors I'm closing that can't be opened at a later date.

I wasn't sure if the frame itself is made differently to accept IRS or if was something you can always bolt on later (even though I suspect it would be very difficult).

Any insight is always appreciated.

-Brew

I have the old IRS and it is inferior to the new one. Having said that I have ridden in three different FFRs with solid rear axle and 17" wheels and I must say the IRS in mine makes the car much more compliant and refined especially around our awful roads here. On the brakes correct me if Im wrong but the "stock" mustang style brakes were designed to stop a 3500-3700lb car, the Cobra will weigh over half a ton less so they should be very good indeed. I'd save on the brakes and get the IRS

[GoDadGo]

I've ridden in cars with the old and new IRS set ups and the ride is better than either of the solid axle configurations; however, I still prefer the rougher riding 3-Link since it plants the crap out of the tires. I also like the simplicity of the set up as well, but that's my dream not yours.

If you want the IRS, then wait a tad longer and get the cash together and then order your kit. Remember that you are planning to build your dream car and you won't be happy with any cut corners and/or compromises.

Good Luck From The Dark Dart Side!

NOTE:... Sounds like a 3-Link for you would be like me having a Ford power plant in front of a 5-speed in my car.
............. It just wouldn't have worked so I wouldn't have been happy so get that I.R.S. because anything else will be a regret.

[caesarmascetti]

quite a bit of it depends on geography, and by that I mean this. I was in southern maryland most of the summer with my Cobra the ride is exceptional but then again the roads are flat and SMOOTH. I got back to PA outside Philly and most truckers and their publications rate us as having the worst roads in the USA and it was an entirely different animal. If I were in a part of the country with smooth roads that had few potholes and frost heaves then I might go solid axle and save the money. But not where I live

[GTBradley]

If you catch FFR when they have their $2500 off on accessories sale you can apply it to the IRS. That’s what I did and then bought a bunch more during the Black Friday sale. For me it had to look the part of a 65’ and perform like a modern day super car. For my wife it needed to be civilized - the IRS can do all that.

[CraigS]

I won't knock Wilwoods for sure but the stock 2015 calipers work just fine. They are significantly better than the old Mustang Cobra brakes and Hawk has pads in several of their good compounds for them. The built-in park brake works very well also. In fact, after 10 ys w/ the old stuff, this is the first I have had a really good park brake. One other advantage that isn't obvious unless you autocross is the IRS brakes don't have any problem w/ pad knock back and resulting lower pedal. I AX on Hoosier A7s so the load is pretty high and I have always had a lower pedal at the end of a run, they worked but the pedal was lower. SInce the 2015 IRS was designed for a high performance car it works very well and I have the same pedal height no matter what. I have old Mustang front brakes and the IRS rears and Hawk HP+ pads front and rear. The car stops unbelievably and the pedal effort is just slightly higher than my Tacoma. So if you order your kit w/ the regular FFR front brakes, use the 2015 rear brakes and the FFR Wilwood balance adjustable pedal/MC assembly you will have all the brakes you would ever need unless you actually race on a track in 20 minute sessions. And I suspect even that could be worked out w/ different Hawk pads.

[BrewCityCobra]

Craig,

Thanks for the input. I am just getting into motorsport (just had my first Autocross with a 944 I've been building a few weeks ago) and am hoping to get on some big tracks yet before the summer ends. I'm hoping track duties can be transferred over to the Cobra once it is built so sufficient brakes for autox and track days are something I was concerned about.

I guess another way to look at it is that if I ever want to upgrade to Wilwoods I always can at a later date - something not really feasible with the IRS.

[BrewCityCobra]

I'm in much the same boat. The wife is on board but if I'm going to get her to actually ride along there will need to be some semblance of comfort.

Is there a schedule for when these deals come around or am I just stuck waiting for one to pop up once I am ready to go?

[GTBradley]

I'm in much the same boat. The wife is on board but if I'm going to get her to actually ride along there will need to be some semblance of comfort.

Is there a schedule for when these deals come around or am I just stuck waiting for one to pop up once I am ready to go?

There does seem to be a seasonal pattern, but I couldn't say for sure. I think they just say "well let's stir up some interest and do another big sale"

[Avalanche325]

I have a 3-link. My friend has the old IRS. I have ridden in, driven and autocrossed both. The IRS feels smoother out on the road. I certainly wouldn't call it a "comfort" ride compared to the 3-link. Just a bit smoother. These cars don't ride as bad as you might think either way. However, they will jar you on a hard bump. They are race cars that you can drive on the street and it is hard to beat that out of them.

I agree that if you want IRS, wait and save up a little longer.
If you want Wilwoods, that is an easy to do later upgrade, even though that costs you more in the long run.

I really doubt that IRS is what will be getting a wife to ride in the car. Wind, noise, exhaust smells, baking in the sun, the car being basic and brutal, etc. are the things that keep wives away from the group cruises that I go on.

[caesarmascetti]

I'm in much the same boat. The wife is on board but if I'm going to get her to actually ride along there will need to be some semblance of comfort.

Is there a schedule for when these deals come around or am I just stuck waiting for one to pop up once I am ready to go?


LOL, for what its worth my wife has ridden in it twice to quote her:

"Its too loud"
"you drive it too fast"
"It smells funny"

[caesarmascetti]

I have a 3-link. My friend has the old IRS. I have ridden in, driven and autocrossed both. The IRS feels smoother out on the road. I certainly wouldn't call it a "comfort" ride compared to the 3-link. Just a bit smoother. These cars don't ride as bad as you might think either way. However, they will jar you on a hard bump. They are race cars that you can drive on the street and it is hard to beat that out of them.

I agree that if you want IRS, wait and save up a little longer.
If you want Wilwoods, that is an easy to do later upgrade, even though that costs you more in the long run.

I really doubt that IRS is what will be getting a wife to ride in the car. Wind, noise, exhaust smells, baking in the sun, the car being basic and brutal, etc. are the things that keep wives away from the group cruises that I go on.


It makes a big difference over potholes and frost-heaves that hit one side of the car and not the other.....ask me how I know. You all in th esouthern US are blessed with some nice roads. I love the area around naples up to tampa and st pete.

[cnutting]

I have the three link on mine and it can be rough on some of our crappy Massachusetts roads. I upgraded my lower control arms to the Breeze Heim joint ones and it was big improvement for a small investment. Still not super smooth, but I didn't go this route for that modern car feel.

[GTBradley]

I really doubt that IRS is what will be getting a wife to ride in the car. Wind, noise, exhaust smells, baking in the sun, the car being basic and brutal, etc. are the things that keep wives away from the group cruises that I go on.

Probably true in my case too, in fact, I’m currently researching dog goggles. But hey, it got her to sign off on the IRS and leather seats, so...

[BadAsp427]

https://www.factoryfive.com/whats-new/factory-five-summer-sale-2019/ Is this not still going on? This was just posted 8 days ago...

[BrewCityCobra]

https://www.factoryfive.com/whats-new/factory-five-summer-sale-2019/ Is this not still going on? This was just posted 8 days ago...

Unfortunately I'm not quite ready yet. Probably closer to the end of the year, so I was just curious is something may be going on around that time. Thanks for pointing it out though.