Indepedent Rear Suspension (IRS) in a 4th Gen
11-17-2013, 08:57 AM
#141
I did not read all the posts in this thread, but why not just put a Jag IRS under your car? Easy to mount, Dana 44 set-up with easy to find LSD, wide variety of gears, and with a few bucks extra, you can put a Watts linkage.
There are numerous Cobras running around with 600-700 hp engines using Jag IRS set-ups. You can get inboard or outboard brakes depending on which year IRS set-up you buy as the donor and they are really plentiful.
There are numerous Cobras running around with 600-700 hp engines using Jag IRS set-ups. You can get inboard or outboard brakes depending on which year IRS set-up you buy as the donor and they are really plentiful.
It the reason that C4 IRS so popular with hot-rodders.
edit: I almost forgot. It accepts stock F-body rims too!
Last edited by Driver_10; 11-17-2013 at 09:14 AM.
11-17-2013, 10:03 AM
#142
I cant speak for anyone else on this forum doing the same swap, but I chose the C4 vette rear end because its lighter than nearly all other IRS packages available. It can be easily extended or narrowed for most custom installs without having to custom fabricate control arms. Just extend/ shorten the drive-shaft, lower control rod, and toe bar and the job is done.
It the reason that C4 IRS so popular with hot-rodders.
edit: I almost forgot. It accepts stock F-body rims too!
It the reason that C4 IRS so popular with hot-rodders.
edit: I almost forgot. It accepts stock F-body rims too!
https://ls1tech.com/forums/suspensio...irs-fbody.html
Finally found the Jag weight's. I knew I had read this before
http://www.mgbv8.co.uk/rearsuspension.html
Differential 108 lbs
Cage and mounts 26 lbs
Calipers and Disks 35 lbs
Lower wishbones 51 lbs
Drive shaft & alloy hub 49 lbs
4 x Gaz shocks 15 lbs
Front tie-bars 7 lbs
Spindles, bolts & washers 9 lbs
Total 300lbs
Last edited by lees02WS6; 01-01-2014 at 12:55 PM.
11-17-2013, 04:36 PM
#143
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Ok. I doubt the Jag set-up is twice as heavy. The normal pictures of it you see have that huge "cage" around it, which is rarely used. My differential is held in place by 4 bolts 3/4" from the top down. There is another mount on each side for the radial arms, and that is it. No huge crossmember to mount. They also use coilovers so no spring to mess with.
I was just curious. Thanks for the info!
I was just curious. Thanks for the info!
11-17-2013, 06:47 PM
#144
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Ok. I doubt the Jag set-up is twice as heavy. The normal pictures of it you see have that huge "cage" around it, which is rarely used. My differential is held in place by 4 bolts 3/4" from the top down. There is another mount on each side for the radial arms, and that is it. No huge crossmember to mount. They also use coilovers so no spring to mess with.
I was just curious. Thanks for the info!
I was just curious. Thanks for the info!
The "messing" with the spring has never been an issue. It's actually less work to go with the monospring since that is the original design. To adapt coilovers on the C4 requires a few extra minor and simple mods; nonetheless, it is more work.
The "huge crossmember" doesn't have anything to do with the complexity of the install. Regardless of its presence or not, you have to fabricate custom mounts. In all honesty I would say the batwing makes the install easier because it allows you to fabricate mounts to the factory frame and its natural position.
11-19-2013, 05:53 AM
#145
Ok. I doubt the Jag set-up is twice as heavy. The normal pictures of it you see have that huge "cage" around it, which is rarely used. My differential is held in place by 4 bolts 3/4" from the top down. There is another mount on each side for the radial arms, and that is it. No huge crossmember to mount. They also use coilovers so no spring to mess with.
I was just curious. Thanks for the info!
I was just curious. Thanks for the info!
The beauty of the leaf spring is that it allows a simplified compact design that is physically more compact than any comparable coil-over set-up. This is especially helpful for tight installs.
Edit: I will say to the credit of the Jag Rear end, with its brakes installed on the diff and away from the spindles may possibly have less unsprung weight than the C4 IRS.
Whether this is actually the case with its steel lower arms, steel half-shafts and over-head coil-overs & dampers, I cant say for sure. But it would certainly look to be the lighter of the two by virtue of the fact that it doesn't have brake stuck to the spindle like the C4.
(the actual overall unit weight of the cast iron/ steel construction of the Jag is a different case entirely)
Last edited by Driver_10; 11-19-2013 at 06:41 AM.
11-19-2013, 09:41 AM
#146
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Foregoing all of the other talking points made, the only reason I deleted the spring was to make way for an altered, cantilevered suspension design to further reduce unsprung weight. (hopefully by 5lbs per wheel)
The beauty of the leaf spring is that it allows a simplified compact design that is physically more compact than any comparable coil-over set-up. This is especially helpful for tight installs.
Edit: I will say to the credit of the Jag Rear end, with its brakes installed on the diff and away from the spindles may possibly have less unsprung weight than the C4 IRS.
Whether this is actually the case with its steel lower arms, steel half-shafts and over-head coil-overs & dampers, I cant say for sure. But it would certainly look to be the lighter of the two by virtue of the fact that it doesn't have brake stuck to the spindle like the C4.
(the actual overall unit weight of the cast iron/ steel construction of the Jag is a different case entirely)
The beauty of the leaf spring is that it allows a simplified compact design that is physically more compact than any comparable coil-over set-up. This is especially helpful for tight installs.
Edit: I will say to the credit of the Jag Rear end, with its brakes installed on the diff and away from the spindles may possibly have less unsprung weight than the C4 IRS.
Whether this is actually the case with its steel lower arms, steel half-shafts and over-head coil-overs & dampers, I cant say for sure. But it would certainly look to be the lighter of the two by virtue of the fact that it doesn't have brake stuck to the spindle like the C4.
(the actual overall unit weight of the cast iron/ steel construction of the Jag is a different case entirely)
05-02-2015, 02:07 PM
#149
There was just an article, within the last two months or so, in one of the Chevy oriented magazines, about putting an IRS into a second gen F-body, using a kit. IIRC, the kit was made by Currie, and the article might have been in 'Super Chevy', since they merged 'Camaro Performers' into it a while back.....
04-01-2018, 02:41 PM
#151
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I just discovered this kit made by Dobbertin Performance Innovations. Its an adapter kit for c5 or c6 suspension cradle. The kit makes the suspension complete as one modular unit. Just add straight frame rails to your build and it bolts in. They also make adapters to run corvette diff, camaro hammerhead diff, 9inch irs diff, or mendeola transaxel for a mid engine setup!
04-02-2018, 07:36 AM
#154
Yeah, no doubt about that. But if you price out overhauling the rear of a 4th gen all at once for maximum performance you're looking at a new Ford 9" complete with axles, crossmembers- everything, rear coil overs, big rear brakes, adjustable torque arm, Watts link and rest of rear suspension upgrades; how far off are you really from the Heidts price?
For someone who tracks their car (road course, auto-x) and is looking for faster laptimes, it's not too far off really.
Their test car ran laps 3 seconds faster with their IRS at Autobahn Country Club in IL - same car with no other mods done, same driver, same tires and near same temps and weather.
For someone who tracks their car (road course, auto-x) and is looking for faster laptimes, it's not too far off really.
Their test car ran laps 3 seconds faster with their IRS at Autobahn Country Club in IL - same car with no other mods done, same driver, same tires and near same temps and weather.
04-02-2018, 11:31 PM
#155
@Heat Seeker WS6:
I totally agree on your price argument. I was seriously considering the Heidts IRS for my car, but ultimately opted for a MWC 9" with watts link and subframe connectors. With my options such as powder coating, aluminum center, and fully assembled, I spent $5,110, and I could have easily spent more if I were planning to drag race or was making more power. That is still cheaper than the IRS, which I previously calculated to be about $8K with options--but with an IRS, you also have to account for things like running custom brake lines, custom parking brake linkage, custom exhaust (I'm doing this one anyway, and the path with the IRS is much better), powder coating (their stuff ships bare), before you even get to all of the custom cutting and welding.
Their instructions are quite detailed, and the parts look to be quality made, so I am very interested to hear your results. I am still waiting on my axle, and that is just one part of a much larger LS3 build, so I won't have any driving impressions from my car for a good while--but when I do, I will be sure to update.
What ultimately steered me towards the 9", apart from the IRS price and extra work mentioned above, were the following: 1) I cannot weld, so I would not be able to do this in my driveway like the rest of the build. 2) Part of the fuel line has to be run into the interior of the car, "under" the back seat, which sounds dicey to me. 3) I'd read another customer of a Heidts IRS (older muscle car, not 4th gen) complaining about bad axle hop and contacting Heidts without resolution. 4) No alignment specs given, which makes me wonder how much testing they actually did on this IRS (they bragged about developing it in only 3 months +1 month of testing). 5) I already have Strano's springs, bars, and Koni on-car adjustables at the rear that I would have to ditch. 6) Their springs have options, but which to choose to match the front Stranos? Their shocks are of unknown quality, so might need replacing for good control. 7) It's irreversible, so if I hate it, the chassis is stuck with it. 8) My car has been "in-progress" for over 2 years now, so anything that is plug-and-play to get it back on the road is preferable.
That said, somebody had to be the first to try the Strano setup or Konis too though, so all the above concerns might amount to a hill of beans if you find that the IRS turns your car into a Vette-killer. Mine is a street car, so I feel like with IRS, the rear could be much softer over bumps while still providing improved grip and roll stiffness if I weren't leaving that on the table to go with the 9". I loved my car before with the Strano springs/bars/Konis and a panhard bar, so I am sure I will love it even more with the watts link. Hopefully you love the Heidts enough to take us all back to school!
I totally agree on your price argument. I was seriously considering the Heidts IRS for my car, but ultimately opted for a MWC 9" with watts link and subframe connectors. With my options such as powder coating, aluminum center, and fully assembled, I spent $5,110, and I could have easily spent more if I were planning to drag race or was making more power. That is still cheaper than the IRS, which I previously calculated to be about $8K with options--but with an IRS, you also have to account for things like running custom brake lines, custom parking brake linkage, custom exhaust (I'm doing this one anyway, and the path with the IRS is much better), powder coating (their stuff ships bare), before you even get to all of the custom cutting and welding.
Their instructions are quite detailed, and the parts look to be quality made, so I am very interested to hear your results. I am still waiting on my axle, and that is just one part of a much larger LS3 build, so I won't have any driving impressions from my car for a good while--but when I do, I will be sure to update.
What ultimately steered me towards the 9", apart from the IRS price and extra work mentioned above, were the following: 1) I cannot weld, so I would not be able to do this in my driveway like the rest of the build. 2) Part of the fuel line has to be run into the interior of the car, "under" the back seat, which sounds dicey to me. 3) I'd read another customer of a Heidts IRS (older muscle car, not 4th gen) complaining about bad axle hop and contacting Heidts without resolution. 4) No alignment specs given, which makes me wonder how much testing they actually did on this IRS (they bragged about developing it in only 3 months +1 month of testing). 5) I already have Strano's springs, bars, and Koni on-car adjustables at the rear that I would have to ditch. 6) Their springs have options, but which to choose to match the front Stranos? Their shocks are of unknown quality, so might need replacing for good control. 7) It's irreversible, so if I hate it, the chassis is stuck with it. 8) My car has been "in-progress" for over 2 years now, so anything that is plug-and-play to get it back on the road is preferable.
That said, somebody had to be the first to try the Strano setup or Konis too though, so all the above concerns might amount to a hill of beans if you find that the IRS turns your car into a Vette-killer. Mine is a street car, so I feel like with IRS, the rear could be much softer over bumps while still providing improved grip and roll stiffness if I weren't leaving that on the table to go with the 9". I loved my car before with the Strano springs/bars/Konis and a panhard bar, so I am sure I will love it even more with the watts link. Hopefully you love the Heidts enough to take us all back to school!
04-03-2018, 07:30 AM
#156
@eb110americana
First off- Fantastic response with great questions and comparisons!
No question that the Heidts is a big chunk of change (even though I'm not quite ready for it yet- since my car is still in pieces w/o motor, trans & etc) it's going to put a biga$$ dent in the checkbook.
I'm in the process of building an LS9 supercharged 6.2LSx that will be run with a custom 6L80E with paddle shift and initially will keep the adjustable Konis & BMR rear suspension setup with LCA's, phr & etc while dialing the car in. For comparison's sake on the road courses I'll switch to a BMR Watts link before going IRS. The car will be mostly street driven too and will see track time on the road courses and auto-X, but no drag racing.
I made it a point to go to their open house last fall and was very impressed- their steel is from the US, and they do a great job on managing quality control with everything they do and how it gets done and test the crap out of things before it goes into production. I used to work in aerospace and was looking very closely at that type of stuff and the fact that they're old school with legit engineering backgrounds was very impressive. They actually have a patent on the design on one of the major parts and there have been no issues with it.
Yeah, their 4th gen IRS seemingly came out pretty quick- almost 'too quick' one would think (I admit, I thought that initially), so you wonder about it's quality and function & etc, but its based on the other IRS systems they've been making and designing for a while already that have proven results and data. They have a 4th gen test car and that's what I got pics of -very nice and clean.
I live only an hour north of Heidt's and plan on having them do the installation and setup; and the track they test at is under an hour south of that. Alternative to that, and my home track, Road America is only an hour north of me so there's more opportunity to dial things in at a proper place while measuring/comparing with data. I'm going to have AEM and AIM data acquisition on the car and with having several thousand miles of tracking under my belt, comparisons should be pretty straight forward.
Like you said, its a serious commitment for the rest of the life of the car- once you go IRS, that's it there's no going back without more major work to the car. I've been lucky to have tracked many types of cars, so it'll be interesting to compare and experience the 4th gen really come alive going through corners like some of the others. Besides vettes, I've got my sights on top of the line Pro-touring cars, Porsches and the brave Ferraris that venture out.
Like my plate reads & means- Heat Seeker: hunt down and kill
First off- Fantastic response with great questions and comparisons!
No question that the Heidts is a big chunk of change (even though I'm not quite ready for it yet- since my car is still in pieces w/o motor, trans & etc) it's going to put a biga$$ dent in the checkbook.
I'm in the process of building an LS9 supercharged 6.2LSx that will be run with a custom 6L80E with paddle shift and initially will keep the adjustable Konis & BMR rear suspension setup with LCA's, phr & etc while dialing the car in. For comparison's sake on the road courses I'll switch to a BMR Watts link before going IRS. The car will be mostly street driven too and will see track time on the road courses and auto-X, but no drag racing.
I made it a point to go to their open house last fall and was very impressed- their steel is from the US, and they do a great job on managing quality control with everything they do and how it gets done and test the crap out of things before it goes into production. I used to work in aerospace and was looking very closely at that type of stuff and the fact that they're old school with legit engineering backgrounds was very impressive. They actually have a patent on the design on one of the major parts and there have been no issues with it.
Yeah, their 4th gen IRS seemingly came out pretty quick- almost 'too quick' one would think (I admit, I thought that initially), so you wonder about it's quality and function & etc, but its based on the other IRS systems they've been making and designing for a while already that have proven results and data. They have a 4th gen test car and that's what I got pics of -very nice and clean.
I live only an hour north of Heidt's and plan on having them do the installation and setup; and the track they test at is under an hour south of that. Alternative to that, and my home track, Road America is only an hour north of me so there's more opportunity to dial things in at a proper place while measuring/comparing with data. I'm going to have AEM and AIM data acquisition on the car and with having several thousand miles of tracking under my belt, comparisons should be pretty straight forward.
Like you said, its a serious commitment for the rest of the life of the car- once you go IRS, that's it there's no going back without more major work to the car. I've been lucky to have tracked many types of cars, so it'll be interesting to compare and experience the 4th gen really come alive going through corners like some of the others. Besides vettes, I've got my sights on top of the line Pro-touring cars, Porsches and the brave Ferraris that venture out.
Like my plate reads & means- Heat Seeker: hunt down and kill
04-05-2018, 12:43 AM
#159
@Heat Seeker WS6:
Thanks for the reply, glad you took mine in the spirit in which it was intended. First things first, you should get Heidts to give you some perks for documenting the install of their IRS here on LS1tech. I mean, the market for it has got to be quite small, and of those crazy enough to shell out for the $8K setup, I would guess most would be on the forums already. If you have positive results to show, you'd be doing them a huge favor in making that information directly accessible to their audience. Plus, you could test out different sets of springs to find the optimal setup recommendations.
That motor you are building sounds like it will be a real beast. What kind of power numbers do you anticipate? It seems we are in similar boats with our cars serving double-duty as both excellent paper weights and money pits at the moment. My engine and trans are already in the car, I just need the rear axle and watts link and then to get a custom drive shaft to fit. I also am having a large part of the interior plastic upholstered and I cut up the steering wheel, so I have to get on that project before I can drive anywhere. I swapped to a newer computer, gas tank, and auto > manual trans, on top of the LS3, so I am sure there will be plenty to sort out once I start it up for the first time. I'm looking forward to seeing your car in the Optima challenge. Keep us posted Heat Seeker!
Thanks for the reply, glad you took mine in the spirit in which it was intended. First things first, you should get Heidts to give you some perks for documenting the install of their IRS here on LS1tech. I mean, the market for it has got to be quite small, and of those crazy enough to shell out for the $8K setup, I would guess most would be on the forums already. If you have positive results to show, you'd be doing them a huge favor in making that information directly accessible to their audience. Plus, you could test out different sets of springs to find the optimal setup recommendations.
That motor you are building sounds like it will be a real beast. What kind of power numbers do you anticipate? It seems we are in similar boats with our cars serving double-duty as both excellent paper weights and money pits at the moment. My engine and trans are already in the car, I just need the rear axle and watts link and then to get a custom drive shaft to fit. I also am having a large part of the interior plastic upholstered and I cut up the steering wheel, so I have to get on that project before I can drive anywhere. I swapped to a newer computer, gas tank, and auto > manual trans, on top of the LS3, so I am sure there will be plenty to sort out once I start it up for the first time. I'm looking forward to seeing your car in the Optima challenge. Keep us posted Heat Seeker!
04-05-2018, 03:04 PM
#160
I've thought about a custom C4 IRS install, but that would strictly be a "I have money in my pocket to burn and I have the need to fabricate something" type of mod.
Heidts unit seems HEAVY.
Heidts unit seems HEAVY.