Why not that many IRS in here

[jfman]

Is there a reason why there are not that many IRS equiped cars in here ?

I did a search on IRS setups hoping to see many different ideas and projects and not much came up except maybe a few rides with a corvette setup, nothing interesting came up.

Any reason why an IRS setup would not be a good idea ?

[novanutcase]

JFMAN - I hear ya'! I have been trying to gather info in terms of this setup for some time now and have come up with a few good things but not enough to say that I have it figured out. I'm not sure what type of car you are thinking of putting your IRS in but if it is a camaro(69?) then 21st century has the answer for you. Yes, it is a C-5 vette setup but I am sure it will be more than what you will need. I for one am looking to put it under my '66 nova and have come up with quite a bit of resistance to this idea. I'm not sure if it is just that people like to stick to the tried and true stick axle but I would suspect that that is part of it. I for one think that the IRS should be explored by these companies that make front and rear end clips since probably most of the people on these forums will not be racing full time and are just looking for something that is a notch(or two) above what the common sports car has in terms of performance.

[jfman]

Ny car is a chevelle and I am looking at cobra and gto IRS's

[Blown353]

I like IRS but it is much more difficult to execute properly. Using an OEM setup is a very good idea as they've already done the homework!

Depends on how much power you run through it too and if you do a lot of drag racing. If you're making big power or a lot of drag racing then a well-designed stick axle setup is probably a better choice. Don't have to worry about snapping half shafts or the seemlngly inevitable wheel hop many IRS setups have. For drag guys, with a stick axle you also don't have to worry about the camber change of an IRS setup affecting your tire contact patch on launch.

A well designed stick axle suspension will do quite well and can put mediocre IRS setups to shame.

IRS is cool, just takes a lot to do it right.

As far as putting either the GTO or Cobra IRS in your Chevelle... I know the Cobra setup is quite heavy and both are prone to wheel hop on launch in stock form (so consider that if you drag.) I know putting poly bushings in the GTO rear takes away most of the hop. Personally, if you're going to go through all the trouble to put an IRS in your Chevelle then why not go C5/C6 transaxle? It works well and will definately help in the weight distribution department. You'll probably have to give up the back seat though.

[jfman]

The cobra and gto unit come already assembled on their own cradle/subframe.
COBRA


GTO





Why not just weld that subframe to the frame of my chevelle?


If it aligned propely an the spring towers are moved on the car, I dont see why this would be a bad idea.




I like the gto setup because it doesnt have any camber and the srping location is similar to a chevelle.

I hear they are weak however.

I think I can retain the back with both of these.


The C5 is not really a stand alone system ans seem like it would be harder to install properly.

[Blown353]

The GTO setup has to have some camber curve otherwise it'll suck in cornering-- because as the body rolls the outside tire will go positive camber decreasing available lateral grip since the tire contact patch is compromised.

The Cobra setup being an SLA-based setup will have definate negative camber gain on compression, which is what you want to maintain grip on the outside tire during cornering.

Stuff like this is why designing a good *effective* IRS is more difficult than designing a good stick axle suspension. With a stick axle you're more limited in design parameters since you don't have to worry about camber/toe change (unless running a cambered housing) and lateral scrub issues... with an IRS setup you suddenly throw FVSA, toe change, lateral scrub, etc, into the mix as well.

Perhaps are the trailing arm mounting points angled in the GTO to give some form of camber gain on compression? There has to be *something* in that IRS to compensate for body roll.

All I'm trying to say is given the effort involved to retrofit an IRS into your car I would want to see you do it RIGHT. No reason going through all the work IMO just to be able to say you have IRS in your car when the setup performs worse than a well thought out stick axle.

Weight is a mixed bag too, usually IRS setups have reduced unsprung weight at the expense of greater overall assembly weight. At least with the Cobra setup I know that will be the case!

[ilovefirstgens]

I have irs...

You really have to weigh your options, Its just opening up a whole big can of worms, and wether you are using c4 c5 or whatever its much harder (and expensive) to upgrade to very high horsepower applications.

And it really sucks wayne dues shop closed because the 21st century setup is far from realistic for most peoples budgets.

[novanutcase]

Actually, as I said in my previous post, 21st century already has the C-5 figured out. I for one will be powering my ride with an LS2 so using the same rear end sort of makes sense to me. Also, if I'm not mistaken the C-5 rear end weighs less than the stang rear so less sprung weight=faster car. A lot depends on how much HP ya wanna make. If your going to do a drag car then, as blown already said, go with a stick axle. If you want a canyon carver then IRS is a good choice especially if you want to drive it everyday(or at least more than just to the road course or drag strip). As far as it having it's own cradle, I'm sure after reevaluating the rear and where you can attach the IRS most of the cradle will be chucked anyways since you will have to modify your own cradle. See this link which will give you an idea what someone is doing with C-5 but totally custom: http://www.lateral-g.net/members/sinjem/

I have spoken to Doug about his car. He went with an SVT diff because at the time noone was making a Vette adapter for the transaxle/diff that the C-5 corvette has. Now 21st Century does so you can use the Vette diff and still have a traditional driveshaft.

[jfman]

Stuff like this is why designing a good *effective* IRS is more difficult than designing a good stick axle suspension. .

Yes but isnt that work all done by Ford and GM already ?

[Blown353]

Yes but isnt that work all done by Ford and GM already ?

Depends on what car you take it off of! They are designed for reliability at stock power levels and predictable, safe handling behavior, and to be cost effective to manufacture.

The GTO setup looks to be far, far from ideal from a handling standpoint being a single trailing arm design. I've driven a few late model GTO's and while they are smooth the limits of traction aren't very high IMO.

The Cobra setup appears better for handling being SLA, but there isn't much adjustability built in and it's a heavy SOB. I've only test driven one Cobra and the salesman didn't let me push the car as hard as I wanted to. Also keep in mind the Cobra IRS has the pumpkin mounted just a bit off the centerline to compensate for torque "wind up"... how far I'm not totally sure but that may mean you could have driveshaft clearance issues.

There are several threads on corner carvers where guys have yanked the 99+ Cobra IRS and replaced it with a Griggs or other TA/PHB stick axle arrangement and had better results. Keep that in mind!

In my experience too, IRS cars are much more unforgiving when taken "past the limit." A good stick axle is usually easier to get back under control once it lets go, while IRS can get very "snappy" and pitch you back around the other way in a big hurry if you're a bit ham-fisted on the steering and throttle corrections. My C4 Vette was pretty nasty when it came to gathering a drift back under control, although the C4 IRS has never been known for "driver friendly" behavior.

[vintageracer]

I believe that you do not see a many IRS suspensions adapted for use in a PT car is the simple fact that the advantage of IRS versus cost of installation is little to none. The development of available bolt in upgrades or simple modifications of most stock suspensions design/arrangements makes IRS installation little more than expensive eye candy for the most non factory IRS cars.

Let's face it, most PT cars never see a track. Hell, most do not see that much street time either. A lot of the suspension modifications made to most PT cars are really just for bragging rights that my car is better than your car when you really get down to it. I can pull 1 G on the skid pad and you can't!

Installing an IRS in your car will be cool. $5K to $10K worth of cool for the cost of the parts and installation? NO. Will it handle better? I doubt it. Will it push your project completion date back 6 months or more? Absolutely!

Stick with something tried and true for suspension modifications for your particular car. Trust me, if you stick with "tried and true" upgrades, your car's handling performance will be much better than your current driving ability to drive your car at its edge of performance. At that point a professional driving school will then be your best performance investment.

[jfman]

My father owns a 2004 cobra and I used to own a GT. Same platform but one with IRS the other one with a well designed solid axle setup.


Night and day difference in the handling departement. The cobra does not handle like any other mustang. It has a much better lateral bite and you never feel the car's rear end wanting to jump over the axle.

I guess the only thing I did not like about the cobra is that you cant have a lot of fun drifting and doing donuts because it sticks so well. And the tires dont wear out as evenly and a str8 axle.

My car is going to be dayly driven with maybe one or two trips to the 1320 a year. Power is going to be coming from a stock ls1.

[Blown353]

The stock GT solid axle setup isn't a good comparison against the 99+ Cobra IRS... now, driving a 'Stang with a Griggs TA/PHB rear setup compared to the Cobra IRS would be a good comparison. I think you would be very surprised.

[novanutcase]

In as much as I agree with Vintage in terms of using something "tried and true" usually will get you good handling characteristics I have to disagree in the fact that IRS will be negligable in terms of performance. Every indy car on the track runs an IRS. Why would that be? Perhaps because they handle better when properly tuned. Yes, I agree that it is harder and more costly to do but if you are interested in pushing the envelope rather than just going with the "tried and true" then IRS is the only answer. I feel that all other forms of rear suspension(3 link, 4 link, 4 bar, ladder bar, PHB, watts, etc.) are all just bandaids for a system that is old technology. Yes, the bandaids work REALLY well but, as I said before, if you are just trying to make your car handle "good enough" then a stick axle is your ticket but if you want to try and push the envelope then I think IRS is a good place to do that.

Ilovefirstgens: What kind of IRS do you have?

edit: I also agree with Vintage about the driving school thing!

[68sixspeed]

I'll chime in one other note- IRS is cool, I have a c5 vette with one, but the fist thing the driving instructors did to us at Lime Rock was scare the crap out of you to make sure any IRS car is 100% straight before going over an uphill corner or it can easily snap around as the suspension unloads. Not as big of an issue with a fixed axel, and having driven both the fixed axel car (camaro) is easier for a novice like me to get back under control if you get the tail end wagging.

Also, yes, big power on IRS can be harder to make work without breakage. I'm not sure on the Cobra rear, but we had a GTO on the lift at work and it looks pretty light-duty-- small axels, etc. I'm actually suprised they hold up to the ls-1 and ls-2 so well, considering the # of people saucing and adding superchargers to these cars.

-Dan

[go-fish]

I was going to do a Heidts IRS, actually have a shop do it. It was going to cut my funds by a 1/3 and take some valuble time. I only had 10 months from one deployment to another. It would be cool but I believe the four bar I did will be nearly as good and the coilovers have alot of adjustability. I don't know about the band-aides thing, there a different systems that do widely different things, crazy band-aides. There are people out here that would never settle for a patch and don't do IRS. I don't think I settled, I chose an alternative suspension. When my car is finished I don't think I am going to be saying, "Dang, wish I had done that IRS."

[ProdigyCustoms]

I have a friend with a LSX / Corvette tuner shop, and I watch Corvettes and GTOs ding the bell north of 500RWHP everytime I go there. Just Sat, a customer I am building a 68 PT Camaro for, had his Procharged 2004 ZO6 on the dyno. Made 760HP and 830TQ to the wheels on the stock rear. I also have watched a many ZR1s go 600RWHP, no breakage. There is a street race 88 Corvette here in town that runs high 8s and hooks on dirt roads, so it can work.

We will challenge Project Prodigy's independent rear next week in Pigeon Forge. I will know Weds when we get the motor off the engine dyno, but we are looking for 750 / 750 minimum FWHP, and we have a C4 rear.

[baz67]

The Indy car comparison is pointless, IMO. One reason they need to use it so they can get the chassis that low. A stick axle will just be in the way. Nascar uses truck arm suspension, so it that better than IRS? In theory the IRS is the better of the two choices. However, in a PT car application it is a toss-up as to which is better. The IRS can be better, but there is alot more room for error in setting up the car. It costs more in time and money to install over a stick axle.

Can you put a factory IRS in your car? Yes, BUT it does not mean it will even handle as good(relative) as its original application. Those suspensions were designed for that specific application and not a Chevelle. Your car may have different f/r weight bias, track width, wheel base, COG, front roll center and weight, just to name a few.

My point is if you want to put an factory IRS in your car, go right ahead. It is your car and you can do whatever you want to it. If you put IRS in and expect a improvement in handling I feel you are in for an expensive dissapointment.

[novanutcase]

But isn't this what most of us are striving for in terms of ride height to lower our center of Gravity? When you are driving the twisties and transitioning from one turn to the other, isn't the contact patch that IRS offers versus a stick axle better? To me the transition is much smoother also since each tire is independent of what the other is doing especially with the inconsistencies on most road surfaces.
In terms of its installation I would imagine that with the "complexity" that is involved in an IRS one would surely seek out someone that is qualified in this area to do this. I will agree that this is not for a "Weekend Warrior" or "Shade Tree Mechanic" to attempt unless he has one hell of a garage and the skills to match. Obviously, Frank Serafine of Prodigy Customs has done it and has the skill and garage to make it happen. I guess we will find out next week!

By the way, Frank, you and I have spoken on the phone on a few occasions('66 Chevy Nova) and I am eager to see how Prodigy does. I'm pretty confident that it will go beyond the expectations that you and your family have for the car. I will be talking to you in a month or so if all the planets align so that we can start on my project. Bummer about Wayne huh?!!??? Any ideas as to who can do the full perimeter chassis? Instead of C-4 I was wondering if we could go C-5 all around? I'm thinking C-5 IFS and C-5 IRS. 21st Century makes an adapter where the 'vette trans goes so that we can still use a drive shaft and use the C-5 diff. What do you think?

[baz67]

But isn't this what most of us are striving for in terms of ride height to lower our center of Gravity?

You can do that with a stick axle as well in his Chevelle.

I just pointing out that by trying to retrofit a suspension specificly designed for another application may not get the results he was looking for. Now if he were to design and install a IRS specificly for his Chevelly he may be better when compaired to a stick axle.

Even if it were theoreticly better would the driving skills be able to take advantage of it. I will use this example. I have the same digital SLR camera and optics as Johnny Huntkins. Does that mean I can shoot a car as well as he can?