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MoeBawlz
12-18-2005, 12:35 PM
Ive seen and read lots and lots of talk on the geometry of a solid axle. But what about IRS? obviously IRS have some advantages over a solid axle in the geometry or all the lemans race cars and many others would be using solid axles and not IRS.

What do you guys know of IRS geometry, as well as compairing it to solid axles in performace as well as practicality and ease of design and fabrication.

MrQuick
12-18-2005, 01:09 PM
thats been a debate for years... it really depends on what the cars usage would be. Road racer street car would benifit more so than a drag street car.

Advantage for IRS, many, camber gain in turns, adjustable castor and toe and better contact patch... you saw "My cousin Vinny" right? Can't explain it better than that. LOL

MoeBawlz
12-18-2005, 01:21 PM
seen it, dont remember it... been a while.

is setting up an IRS that much harder than a solid axle?

Steve1968LS2
12-18-2005, 02:33 PM
An IRS is usaully stated to have less unsprung mass but it has much more sprung mass, it ends up mostly a wash.

Hard to get good anti-squat with and IRS.. many a new Cobra owner has ripped out the factory IRS and gone back to a live axle..

I would think an IRS system would be harder to install than say a three or four link equipped live axle. It really comes down to how you expect to drive the car.

toxicz28
12-18-2005, 03:47 PM
seen it, dont remember it... been a while.

is setting up an IRS that much harder than a solid axle?


This will refresh your memory.
Mona Lisa Vito (http://www.imdb.com/name/nm0000673/): No, there's more! You see where the left tire mark goes up on the curb and the right tire mark stays flat and even? Well, the '64 Skylark had a solid rear axle, so when the left tire would go up on the curb, the right tire would tilt out and ride along its edge. But that didn't happen here. The tire mark stayed flat and even. This car had an independent rear suspension.

ProdigyCustoms
12-18-2005, 04:33 PM
Long story short, a chassis car with a good IRS set up like a C5 / C6 that uses upper and lower arms, properly set up, will be very hard to beat. But the new DSE 4 bar with the swivel bars, and the LD 3 link will put up a good fight.

For me, total hardcore...... Full chassis and independent.

RobM
01-15-2006, 12:04 AM
On a perfectly smooth and level skid pad a solid axle will have just as much cornering power as and IRS with unequal length control arms. If the IRS isn’t set up right the solid axle will most likely be even better.
The down side of the solid axle designee is the second one tire hits a bump in a solid axle car it’s going to give a compromised contact patch to both tires. Even a car with a solid axles FRONT AND REAR (early nostalgia hot rod style I- beam double wish bone) technically would handle well on a flat smooth surface because the tires have no choice other than to use their entire contact patch, that’s technology from the early 1900's!. of coarse once the road gets bumpy this goes out the window.
I personally think IRS has more stuff to go wrong and is over rated. Id go with truck arm or a good three or even four link with a solid axle. Just remember the secret to handling is to keep the tires contact patch as large as possible. Suspension in a race car isn’t for comfort its to keep those tires planted. This is why a go-cart, a vehicle that is immune to body role for all intensive purposes handles so well. The bottom line is the tires are always in 100% contact with the road no matter what

baz67
01-16-2006, 07:39 AM
This is why a go-cart, a vehicle that is immune to body role for all intensive purposes handles so well. The bottom line is the tires are always in 100% contact with the road no matter what

At least until roll stiffness lifts the inside front in a corner. :poke: Other than that I agree 100%.

I feel solid live axle with a link style suspension is the better choice for a PT aplication over a IRS. Yes, the IRS can be better. However, it is also more complicated to install and tune.

boodlefoof
01-16-2006, 10:38 AM
Steve,

Where would the extra weight come from with the IRS? A solid rear is pretty heavy... I would think an IRS system would weigh less even with control arms and such. Or at least it would be close.

What about running a transaxle and eliminating the differential all together in an IRS system. Seems like this would save some weight too and shift some weight to directly over the rear tires.

MrQuick
01-16-2006, 11:47 AM
Where would the extra weight come from with the IRS? from the extra bracing,axles are pretty heavy,links and such, But like everything eles,can be made with lightweight material then you start getting expensive. Unless you make everything yourself.

ProStreet R/T
01-16-2006, 01:01 PM
IMO when looking at something like this you need to seriously consider what you want the car to do, your budget, and mechanical ability.

For a comfortable street car that will handle extremely well IRS is great. You can use stock vette, cobra, or viper rear ends and have most of the components ready to go. But as was stated the overall weight is a bit more than a nice solid axle. Unsprung will be less, but more complicated to setup. Also consider what kind of HP you will put through it. To keep it reliable I put the limit right around 800ft/lbs, beyond that you start killing parts. I have seen many vipers literally rip the center diff section out of the car. It takes a good bit of bracing to support that kind of HP. But even before that you have to run a $1200 set of titanium half shafts to put the power to the wheels. It's far from an economical build.

For a reasonable price you can get a nice 9" built, 3 or 4 link, and when setup properly will handle well enough that 95% of us will never need anything more. Plus it will handle all the power you even dream to push through it. Even in the event you did break something, it's a $500 ring and pinion, not a $2000 pumpkin, and $1400 quaife diff.

Also do some research, contrary to popular belief you CAN run camber on a solid axle. I know it sounds crazy but it can be done with the right setup.

David Pozzi
01-17-2006, 08:45 PM
The old IMSA GTO class allowed only stick axle rear suspension on cars like Camaro and Mustangs, but Corvettes could run independent of any kind, (quick change center section) or a solid axle. The DeAtley team with David Hobbs driving, switched from Camaros to Corvettes, they were winning with the Camaros, the Corvettes with independent suspension didn't work very well, they wore out the rear tires early in the race, traction out of corners late in the race was a huge concern for those cars. They eventually got the cars working better, enough to quit running the Camaros they had, but there was little difference between them on a race track.
Perhaps some other application/situation would show up differently.

A lighter race car like an open wheel forumla car, would have a very large proportional amount of unsprung weight which could become a problem, that's why lighter race cars benefit more from independent rear suspension. Also independent rear suspension has less anti-squat, so it works better on car with a rear weight bias.

Norm Peterson
01-19-2006, 06:45 AM
Either a one-off IRS or one adapted from a significantly different car will be trickier to get set up such that you could/would take full advantage of the benefits. It's quite possible to be less comfortable sooner with an IRS, in which case you simply won't drive it as hard as the components would permit. You'd be both faster and more comfortable about it with a good stick axle setup.

boodlefoof - isn't that the C5/C6 solution? And others before it, such as the Porsche 928? Anyway, that approach trades off weight distribution improvements against polar moment of inertia increases. Arguably a good thing where driver capabilities are unknown (as is the case for the OEM's, their high performance offerings, and their targeted range of customers) or for high speed events. Not such a clear advantage at something like auto-x in a 3000+ lb car (might be course-dependent, involving specific slalom details).

Norm

boodlefoof
01-19-2006, 08:40 AM
Norm,

Yeah, the Prosches have been using transaxles for awhile (the G50/50 is pretty popular amongst GT-40 kit car builders). The vettes seem to do it a little differently though... I think they have a separate differential mounted directly at the tail of the trans, whereas the transaxles I'm talking about (like the Porsche) integrate the diff inside the actual trans case. The axles then come out right in the middle of the trans as opposed to right behind it. I'm not sure of the weight difference between these two though.

deuce_454
05-29-2006, 11:11 PM
ive adapted a jaguar IRS to my 32 roadster, its basically a dana 44 center section, inboard disc brakes, double wishbone rear suspension, although the upper "wishbone" doubles as a driveshaft, so it can sit as high under the frame as a stiff axle is, the unsprung weight is about 20 pounds per side and moving the anchorpoint for the longitudinal controllarm is no different than moving the intersection point of a 4 link...

as for titanium halfshafts... i shortened the oem halfshafts and used a solid 40mm OD chrome/vanadium steel bar... totally overkill but im sure ill be spinning the rims in the tires before i break one...

slow4dr
05-30-2006, 09:37 AM
I am going back and forth between the two myself. I have been in contact with Mark @ LD and he is nearby so I'd love to go with their 3-link route. However I actually feel the IRS would be less expensive for me because I can do most of the fabrication myself.


IRS:
used C4 Vette IRS usually under $1000
Dana 44 upgrade $1000-$2000
sell the Dana 36 and recoup some $$$$
shortening control arms $cost of wire & gas
Shortening half shafts $cost of wire & gas
misc mounting hardware $100
The C4 already has decent brakes from the factory(with e-brake).
The only thing that could be interesting/costly is if the stock leaf spring & sway bar can't be modified & reused. Even if I added $1250(see below) it would still be less expensive than a bar set-up.

Total $3100 (worst case scenario)

3-link or 4-link:
reinforced 9" rearend $500
center section $500-$750
axles $500
watts link $500
Chromoly links for bars $300-$400
brakes $1000
Chromoly bars $200
shocks/springs $500-$1000
sway-bar $250

Total $5100 (worst case scenario)


I am an avid drag racer and I wouldn't run the IRS if I wasn't confident it could be made to 60 ft well. I know a lot of the Cobra guys swap to a solid axle but I also know some Supra/Viper guys pulling 1.3 short times with factory IRS's.

deuce_454
05-30-2006, 09:59 AM
why not go with the jag unit, it is already a dana 44, albeit with 10 spline pinion and 9/16 ring gear bolts, but a dana 44 bolts right in (i know first hand).. i got mine for 500 bucks, locker, inboard disc brakes, e.brake, add cost of gas and wire for shortening and fabricating the mount and you are motoring.... a good friend of mine gets 1.5-1.6 sec 60 foot times with a procharged LT4 and 2600 stall in a 3000 pound 31 ford hot rod (with him in it) running a jag suspension and 275/60-15 drag radials (700R4, no transbrake, 3.54:1 rear ratio)

that is very decent in my book...

deuce_454
05-30-2006, 10:05 AM
Sweet nova BTW, is that where you were considering IRS??

slow4dr
05-30-2006, 11:13 AM
why not go with the jag unit, it is already a dana 44, albeit with 10 spline pinion and 9/16 ring gear bolts, but a dana 44 bolts right in (i know first hand).. i got mine for 500 bucks, locker, inboard disc brakes, e.brake, add cost of gas and wire for shortening and fabricating the mount and you are motoring.... a good friend of mine gets 1.5-1.6 sec 60 foot times with a procharged LT4 and 2600 stall in a 3000 pound 31 ford hot rod (with him in it) running a jag suspension and 275/60-15 drag radials (700R4, no transbrake, 3.54:1 rear ratio)

that is very decent in my book...

What is the typical track width on the jag rear? That could surely be another option and maybe one better suited for an early Nova.

Yes, this will be for the Nova in my sig.

deuce_454
05-30-2006, 01:48 PM
the im almost sure that you will need to shorten it to fit under the nova, unless you stumble upon one from an e-type.. ill measure the unshortened one i have for spares tomorrow and post specs, but im sure the info is on the internet somwhere... but the jag unit is prety much what kugel has copied... take a look at http://www.cwiinc.com/ in the mean time...

slow4dr
05-30-2006, 02:08 PM
the im almost sure that you will need to shorten it to fit under the nova, unless you stumble upon one from an e-type.. ill measure the unshortened one i have for spares tomorrow and post specs, but im sure the info is on the internet somwhere... but the jag unit is prety much what kugel has copied... take a look at http://www.cwiinc.com/ in the mean time...

Interesting, thanks for the info. Weight is a concern as well which is why I have leaned away from using the Cobra IRS. It would be interesting to see actual weight #'s to compare all of them(both sprung & unsprung).

RobM
06-01-2006, 07:36 PM
im pretty sure its dificult to get any sort of anit squat with irs.... corect me if im wrong irs isnt my game

deuce_454
06-02-2006, 03:45 AM
well actually it isnt thar hard... but it requires that you think "4 link" when you decide where to attach the longitudinal controll arms, the IRS will (just like a rigid rear) react when you transfer torque to the wheels, where this reactant force, and in what direction relative to the C of G ot the chassis will determine if it squats or raises the rars, and also the amount of weigth transfer... but like designing a solid axle suspension, it requires knowledge of the forces in question and desicions on how tou want the car to react..

RobM
06-02-2006, 04:00 AM
makes sence thanks, I dont see how you could get as much anti squat as a solid axle with links, but then again how much is really needed?

Norm Peterson
06-02-2006, 04:33 AM
I don't think it's realistic to expect as much A/S with IRS as with a solid axle, at least not before you compromise other aspects of the IRS arrangement to the point of losing more somewhere else than is marginally gained with the last increment of A/S increase (rear toe change with suspension travel comes to mind).

Norm

Mean 69
06-02-2006, 08:31 AM
The physics behind the IRS versus the stick axle regarding A/S are completely different, as are the equations that are used to calculate them. Literature suggests that about 25% A/S for an IRS is the practical limit, going beyond this is going to start really compromising the rest of the suspension attributes. IRS systems are obviously really great systems, but because of their relative complexity and various interactions of all of the suspension considerations, you can get lost REALLY fast with them.

A/S for a stick axle can easily be far hgiher, which means there is "potential" to plant the tires harder as a result of reactive forces, but here again one needs to really understand what the primary goal of the setup is before going too far (for instance, the biggest enemy of very high anti-squat and the corresponding short SVSA's is brake hop, not a good thing).

Nothing's free.
Mark

hssss
06-08-2006, 12:32 AM
I am building a 351/392 powered Lotus 7 and am currently debating the relative worth of IRS vs a 3 link similar to the 05+ mustang. My problem is that unspring weight with the solid axle will be a large part of the overall weight. I can fairly simply fab either setup and using only selected Cobra parts, hubs for 5 on 4.5 and dif drive flanges for 31 spline (already have a Torsen T2 31 spline) the rest from a MK VIII. The more I look the overall weight probably would be about the same but the setup will be more complicated. The primary problem I have heard about the Cobra setup is that it is geometry challenged. For the Nova I would think the C4 setup would be the least complicated to install.

deuce_454
06-08-2006, 11:59 PM
the jag rear suspension is in it self not geometrically challanged, but ive seen a couple of companies who sure screwed up in designing the mounting... the challenge you are refering to is that the LCA in th ejag suspension also transfers torstonal forces, where as that is dealt with in the longitudinal CA in a corvette setup.. that means that if the jag carrier is rigidly mounted the longitudinal CA will break off the bolts holding the LCA bracket to the carrier unless the forward mounts of the longitudinal CA are mounted on a line that intersects with the LCA inner bearings. and if thsi is not the case then the carrier must be mounted so as to allow it to swing... (which is also how you enable antisquat)

hssss
06-09-2006, 12:19 AM
...The primary problem I have heard about the Cobra setup is that it is geometry challenged...
Note

Protour_Pinto
06-11-2006, 08:33 PM
And if the rearend dosnt work out you can always make furniture out of it!

https://static1.pt-content.com/images/noimg.gif

I went with a Jag rear in my car due to cost and my cars driveshaft was only 20 inches long. The pinion had to be stationary.

If you go to Pick A Part you can pull a whole rear assy for $250.00

hssss
06-11-2006, 09:01 PM
Protour_Pinto I like your furniture but you must not be married. I have decided to go with a Roarty http://locost7.info/files/suspension/RortyLocostIRSAssembly.pdf based Irs using late Explorer dif and MK VIII spindles, they are infact inroute as we speak. I like that the 8.8 is a bit stouter than the D44 and this design gives me a bit more wiggle room in the fabrication.

daveheld
09-25-2006, 06:54 PM
I like the IRS TV stand... I have a table that would go well with it...


https://static1.pt-content.com/images/pt/2006/09/TopView3-1.jpg

dave
Cocoa Beach FL

Twin_Turbo
01-04-2007, 01:58 PM
I built a custom double a arm IRS using a C4 corvette super dana 44
https://static1.pt-content.com/images/pt/2007/01/roller13-1.jpg

https://static1.pt-content.com/images/pt/2007/01/roller12-1.jpg

https://static1.pt-content.com/images/pt/2007/01/82chassis1-1.jpg

Samckitt
01-04-2007, 02:54 PM
Twin Turbo, Any chance you would share the CAD file of the factory Vette rear that you have modeled?

Samckitt
01-04-2007, 02:56 PM
Daveheld - I love that table, I'm gonna have to make one of those.

Twin_Turbo
01-04-2007, 03:20 PM
Twin Turbo, Any chance you would share the CAD file of the factory Vette rear that you have modeled?

Which one do you need? early cast iron w/ lid or w/ 80-82 batwing ?

Shoot me an email, I will send you the file later this week, have it on another system

telite
01-05-2007, 11:32 PM
i like the twin turbo^ setup.
and the old pantera setup. real nice fully adjustable.

Twin_Turbo
01-10-2007, 04:18 AM
Scot, did you ever get those models I sent you??

Samckitt
01-10-2007, 05:37 AM
Yeah I got them, thanks. I have them imported into UG & have made the assy. I'll have the model the half shafts, hubs & the upper & lower arms.

I have to find a new batwing cover for the one I have. One of the "wings" is bent on the one I have. Paul Newman's Car Creatins sells a new redesigned casting that is heavier & has some supports inside for the bearings. $800! Ouch.

Thanks

Twin_Turbo
01-10-2007, 06:08 AM
Why not just cut off the batwing all together and put togethre some kind of subframe to mount it, there are plenty of oints on the diff where you can mount it, like the stock camber rod moutns, the front c beam pad... just like mounting a quick change. This could easily be made stronger than the batwing.

Do you have a model of the halfshafts? I have it, the length is easily changed...if you want it, let me know.

Samckitt
01-10-2007, 06:21 AM
I have thought of doing that. Might be the way I end up going.

I quickly made some half shafts. I don't know if they are the correct OD or length yet. I did not measure what I have. The ends are probably nto correct either. So yeah if you don't mind, it will save me a little work, send what you have to me please.

Thanks.

Twin_Turbo
01-10-2007, 06:50 AM
my models are for 3" OD shafts w/ 1350 yoke ends. I'll send them your way.

J68Bird
01-10-2007, 11:54 AM
Scot,
I was able to fab up my own "Batwing" using the files that you sent me. I found a local Corvette place that would have sold me one, but it was about 6" too wide. I'm using a C3 rear. I've got all the parts made and as soon as I get the center section powder coated I'll be putting it all together.

J. Clear
68 Firebird 455/4spd Conv.

https://static1.pt-content.com/images/pt/2007/01/rear_clip-1.jpg

Twin_Turbo
01-10-2007, 12:16 PM
That looks like an eaton diff, I sent scot the models for that one. The late C3 (80-82) uses a batwing similar to the C4 one. Like your mounting systen. How are you mounting the pinion? I'd advise you to use a heavy duty lid, the non HD ones have significantly thinner ears (original leaf spring mounts) and they crack quite easily.

Looks like you are building a trailing arm IRS? Nice, please keep us updated on it, I for one would love to see it.

Samckitt
01-11-2007, 06:17 AM
J68bird - Looks good.

I was reading some yesterday & found that the D36 batwing can be used on the D44, looks like there is an adapter plate of some sort between them. What is different between them besides the extra bolt hole on the D36 cover?

J68Bird
01-11-2007, 06:28 AM
TT
The rear I have is an early style, '68 I believe. This is the first I've heard about the "lid" being weaker, but this is all pretty new to me. Not sure if mine is the HD style or not. I've got a pinion mount made and will try and get a few pics. (didn't model that one yet)

Scot,
When I talked to the Corvette guy he mentioned something was different about how the newer style bolted up. I remember looking at the piece and thinking that it wouldn't be problem to drill new holes to make it work. Unfortunately, now I can't remember exactly what the difference was.

J. Clear

Samckitt
01-11-2007, 07:44 AM
Maybe the internal cast bosses for the bearing cap supports are in the wrong place.

Scot

Twin_Turbo
01-11-2007, 08:41 AM
TT
The rear I have is an early style, '68 I believe. This is the first I've heard about the "lid" being weaker, but this is all pretty new to me. Not sure if mine is the HD style or not. I've got a pinion mount made and will try and get a few pics. (didn't model that one yet)


If you have an original diff you always have the weaker lid, ther HD is stricty aftermarket. Also, if you have a 68 or other early year (pre 72 I think it was) you also have the weak posi case with the small square window and the weaker 18-10 spider gears, the later large teardrop window case and the 17-10 gears are much stronger. You can easily see if it's HD or not, the moutning flange is much thicker on the HD one and the reinforcement rib that runs to the yop shaped like a ) is less deep there also.

The later differentials use a batwing like the C4 corvette, the pre 80 eaton unit (cast iron, what you have) uses a bolt on crossmember on the top of the lid. That's the difference, there's also a difference in the camber bracket and how that's setup (earon bolts to main case on the bottom, dana alu C3 80-82 and C4 bolts over the lid to case mating flange)

pdq67
07-08-2007, 02:29 PM
Anybody ever think about playing w/ the old Pontiac Tempest transaxle swing-arm rearends??

I think that they were only in the '63 and '64 Tempest cars back then.

I don't know if a 4-speed was ever offered, but do know that they were auto and 3-speed stick back then.

pdq67

Atrain
07-11-2007, 06:52 AM
I put a 90 vette IRS and 6-speed in my '70 Camaro. I am still a long from being done with the car though...

https://static1.pt-content.com/images/pt/2007/07/Camaro002-1.jpg

jeffandre
07-14-2007, 09:37 AM
I put a 90 vette IRS and 6-speed in my '70 Camaro. I am still a long from being done with the car though...

https://static1.pt-content.com/images/pt/2007/07/Camaro002-1.jpg

Cool, get more pics and use it. Looks like a sway bar mount attached to the underside of the trunk? Might need some sort of rigid support for that one, the trunk floor will flex more than you think, even though it is welded to the gas tank support metal. Have you beefed up the trunk pan from inside?

Atrain
07-14-2007, 06:44 PM
I had to pin a few things together in a hurry before our move...but thanks for pointing that out. No meaningful bracing for the rear sway bar yet, it will probably come off the cage inside the trunk. I need to buy my fuel cell first and get that sorted out. With two small kids, and tons of body work to be done (which I can't stand), my project is moving pretty slow so I don't see a test drive in the near future, but I will snap a few more pics of the rear end for you. I'm learning as I go with this so I'm definitely interested in people's feedback. Drivetrain is the vette D44 with 4:10's, ZF 6 speed (the black tag one), and a 500 HP 383 with a cheater system. It's going to be a retro-ish trans-am racer kind of thing.

Norm Peterson
07-15-2007, 04:04 PM
What you'll want for reinforcement is something that runs laterally from frame rail to frame rail. Fairly rigid, too, as any flexibility of this supplemental framing detracts from the effectiveness of the bar (making it behave like a smaller bar) The way the rear sta-bar works requires that it resist the roll of the chassis as a whole, so you need to tie back to major chassis structure.


Norm

Texas Hotrod
07-15-2007, 08:59 PM
I finished my all-custom sub frame and have the Crown Vic (police car) aluminum (almost all aluminum) front suspension unit bolted in. It's finally all mounted to the Camaro. The Ford suspension is roughly 4" wider than what the 68 Camaro had, so now my Z06 wheels should fit nicely. Now on to the next phase.

I had a blazer 12 bolt (w/machined and redrilled axles) mocked in with 10.5X18" wheels and tires installed. The truck axle is 6" wider than the stock Camaro 10 bolt, making the Vette wheels fit perfectly inside the rear fenders.
All the hard work that went into the front frame and I just couldn't stand not having an IRS in the back. I did some measuring and figured out that the 12 bolt truck axle is the exact same width as the Vette unit. I dropped the axle, pulled the mono-leafs and took more measurements. I'm surprised that the mounting points of the bat wing line up with the boxed sections under the car. It looks like I can make this work as well.

I purchased a stick of 3X3 thin wall tubing and started fabbing the mounting for the BW. I need to hang the center unit first and then I'll verify if I can retain the Vette torque arm. I have the engine mounted (w/custom motor mounts) and the tranny is jacked up into position, I just wasn't quite sure about the crossmamber. The strange thing about Corvettes, they don't have crossmsmbers. If I can tie the torque arm into the back of the tranny, then the Camaro won't need a crossmember either. Running 3" duals will then be a lot easier to install.

I own an '88 C4, so I have the luxury of easily getting measurements first hand. For what it is, the C4 is a fine car. Anti-squat????? I have never noticed mine squat in a hard launch, I guess I'll have to pay more attention next time I drive it. Even hard on the gas/hard o the brakes it tracks stable and true.
My friend's C3 has totally different issues. His has major squat under power/shifts. Then again, C3 is a crappier system. It's mostly made of steel (the C4 is all aluminum) and the torque point is directly above the pinion yoke. The C4 ties the torque arm to the transmission tail shaft, which transferres all the lifting forces from the rear end up to the motor mounts.
The Corvette rides nice and handling is crisp and precise. Taking the same car and adding a straight stick in the rear would be detrimental, it would be a totally different car (more of a Camaro????). The same goes for adding the IRS to a Camaro, It'll make it more of a Corvette. In all reality, it does need to be engineered correctly. Will it out perform a 3-linked (or a 4-link) properly set up 9" in a hole-shot? Maybe not, but that doesn't mean it can't be raced either w/o good results. Then again it's a pro-tourer, not a pro-streeter. Each one has its place.

I've heard all the sad stories from many different people about my IRS install. Each of them had owned a Camaro (or a Mustang) at one time, but none had ever owned (or even driven) a Corvette.
So coming from a Vette owner/driver, if it's IRS that you want, then go for it and don't let others second-guess your decision. Just make sure it's done correctly.
Post pics as you progress.

Good luck,
Gene

Atrain
07-18-2007, 04:54 PM
Here are some additional pics of my C4 IRS install into my 70 Camaro. I'm embarrassed that I let things get so rusty. Like I said before, it was a rush to make it a roller before we moved, and of course we hit a storm on the way...likely because I neglected to paint things. Anyway, in the interest of knowledge, here you go. Please feel free to make constructive suggestions as I am new to this...

https://static1.pt-content.com/images/pt/2007/07/Camaro026-1.jpg

https://static1.pt-content.com/images/pt/2007/07/Camaro030-1.jpg

https://static1.pt-content.com/images/pt/2007/07/Camaro029-1.jpg

https://static1.pt-content.com/images/pt/2007/07/Camaro028-1.jpg

https://static1.pt-content.com/images/pt/2007/07/Camaro027-1.jpg

Texas Hotrod
07-18-2007, 05:00 PM
Does the spring rate seem stiff for that car? I'll retain my spring too, I just wondered if it was too stiff. Might be hard to tell w/a gutted interrior as I'm working w/a bare shell also.

Atrain
07-18-2007, 05:26 PM
It seems pretty stiff but so did the vette I took it out of. Really too hard to tell until the car is put together and driven...

hossdoc
08-02-2007, 03:25 PM
[quote=RobM] Id go with truck arm or a good three or even four link with a solid axle.

With regard to the Four link; Do you have to worry about significant binding under hard lateral acceleration. I can forsee that a streetcar might never experience this, however if I intended to autocross or open track the car might it be detectable?

68sixspeed
08-02-2007, 05:59 PM
With regard to the Four link; Do you have to worry about significant binding under hard lateral acceleration. I can forsee that a streetcar might never experience this, however if I intended to autocross or open track the car might it be detectable?

I can shed a little light and almost 20K miles of experience on a 4 link - If you leave it set for optimal drag settings, you have little to no roll ability in the rear, but, 15 minutes, move the lower link closer to parralell with the ground and if need be level out the upper link some, it behaves closer to a 4 bar setup and I can get 2.5"+ free roll; add some upper links with birdcages and urethane springs and it rolls even more and takes the tire shock out of it exitting the corner. Even on street/cornering settings the 4 link works well and has zero wheel hop. Yes, it does weight transfer a lot better on the drag settings, but it does good on the cornering settings too. (it just won't hang the front end unless it is on drag settings.)

Back on topic, IRS is cool, but unless you have a bumpy track I'm not sure if you would notice it. Ever drive a newer vette with the traction control off? They are all over the road in 1st and 2nd gear-- no weight transfer. A good 3 or 4 link on a fixed axel can weight transfer a lot better.

-Dan

Norm Peterson
08-03-2007, 02:59 AM
[quote=RobM] With regard to the Four link; Do you have to worry about significant binding under hard lateral acceleration. I can forsee that a streetcar might never experience this, however if I intended to autocross or open track the car might it be detectable?
If you're talking about triangulated 4-links a la A/B/G body, you do. But the 'bind' issue there is a function of what you've got in the ends of the links for bushings rather than the fact that you've got four links. It is a case of the stiffer you make the bushing material the worse it gets, and could amount to 50 lb/in or more at the wheels. Since this effect more or less works in parallel with your springs and sta-bar, stiffening those components will reduce the bushing effect.

If you know what you're looking for, or even if you don't and make immediately-before and immediately-after drives over certain types of pavement unevenness at low speed, you can clearly feel the difference in ride with only four of the eight rear bushings swapped from OE rubber to poly (as most such bushings are sold).

Four links is kinematically the correct number for a stick axle, so there isn't any inherent bind as long as the links can only carry axial loads (i.e. no bending, torsion, or shear). However, that doesn't address other issues even if the links are all rod-ended and the amount of 'bind' really is negligible - for example, I'm not at all sure what path the axle follows in roll (it may not be pure rotation).


Norm

68sixspeed
08-03-2007, 01:05 PM
One thing that hurts a 4 link in roll is hard to picture at first, but the easiest way to describe it I've found is to consider the pinion angle change-- If you have some 'up' angle in the lower link as you would want to plant the tire, then as the suspension is compressed the bottom brackets move rearward sligtly and the top brackets move forward slightly making the pinion nose down under compression. If only one side of the car is being compressed in this situation the axel will just lock up in roll and be force to compress both sides evenly. (as one side of the car is trying to hold the pinion angle constant and the other is trying to move it up/down - trying to rotate the rear end housing.) Rubber bushings help this by allowing some stretch, but it's a length of bar issue, not a swivel/rotation issue with the rod end or bushing. To help this, you can set a true 4 link to more of a 4 bar setup by bringing the bars more into parrallel which minimizes pinion angle change and twisting of the axel tubes. (for example, I've heard of pro-street cars actually break rear end tube welds from the tube stress of street driving.) I hope that makes sense... -Dan

pdq67
10-13-2007, 11:51 AM
I'mmmm Baaaack!!!

Well, AGAIN, has anybody ever thought about using the old Pontiac swing-axle transaxle by limiting the swing-axle's movements so they can't jack!!

Seem's I've read where I wanna say Smokey or maybe Jenkins used to race an early 'Vair up Pikes Peak and whipped some folks b/c he got the axle-jacking deal figured out!!

May be wrong on the guys, but still............ Early Ralph Nadar kid-killing 'Vair!!!

And if I was to create an IRS, I'd use a 9" pumpkin and top and bottom locating triangle/A-arm shaped, one-piece mono-leaf springs to locate the axle ends like the front suspension's A-arms and be done w/ all the Mickey Mouse crap used to locate it now!!

Except for the sway-bar and maybe a z-bar too...

pdq67

maldo
08-15-2008, 11:30 AM
This will refresh your memory.
Mona Lisa Vito (http://www.imdb.com/name/nm0000673/): No, there's more! You see where the left tire mark goes up on the curb and the right tire mark stays flat and even? Well, the '64 Skylark had a solid rear axle, so when the left tire would go up on the curb, the right tire would tilt out and ride along its edge. But that didn't happen here. The tire mark stayed flat and even. This car had an independent rear suspension.



LOL LOL I can hear that in her NEW york voice :jump: she so hottttt :drool:

BillyShope
01-21-2009, 05:54 AM
Road racer street car would benifit more so than a drag street car.

Usually, but there's some misunderstanding here regarding dragstrip requirements.

The maximum effort...cornering OR tractive...from a tire pair is achieved with equal loading. While equal loading is essentially inherent with an IRS, the same is not true with a RWD car with beam axle. The driveshaft torque tends to unload the right rear.

So, why aren't there more IRS cars at the dragstrip? There are a couple of reasons. Durability was a problem with some of the earliest IRS units available to dragracers and, for this reason alone, most won't consider them.

But, probably the greater reason involves that which is called "hit" or "separation" on launch. In terms more common to this forum, dragracers feel they need more than 100% antisquat. While it's certainly true that such an arrangement provides additional initial loading of the rear tires, the dragracers seem to forget that "what goes up must come down."

So, with the design difficulties involved in achieving antisquat values even close to 100%, it's not difficult to understand why a Viper owner would succumb to dragstrip comments like: That car'll never be competitive with all that squat.

I wonder, however, how many Viper owners have never equalled their IRS 60 foot times after switching to a beam axle. I know of at least one IRS Viper that is doing very well.

It is possible, of course, to achieve equal rear tire loading on launch with a beam axle car, but some form of suspension asymmetry must be present to cancel driveshaft torque effects. My site is largely devoted to a discussion of these various forms of asymmetry. If you're interested in this sort of thing, I would direct you to Page 18, where there exists a spreadsheet for the setup of a 3link for equal rear tire loading. The spreadsheet allows the input of a desired antisquat percentage and has recently (within the last couple of days) been updated to take into account the unequal dynamic spring forces when antisquat is not 100%. (For this change, I had to assume that 40% of the roll stiffness is at the rear. If you really think you need more accuracy, you can copy the source for your own HTML file and change the .4 factor to something else. Considering the tolerances of the other parameters, I don't feel this is necessary.)
http://home.earthlink.net/~whshope
over 130,000 visitors

van454
01-24-2009, 08:30 PM
This is an interesting discussion, I have been thinking about IRS for my 3rd gen Trans Am, and I was thinking C4, but maybe the Jag set-up is a better option? Has anyone looked at the 04-05 GTO set-up?

calforniacuda
01-25-2009, 02:04 PM
Used C5 spindle, control arms, hubs, are pretty cheap. If you can live with stock track width the aluminum cradle for lower control arm mountings can be used. Suspension analyser program has free sample with location of control arm mounting points.

Not necessary to use C5 rear diff, 8.8 ford can be used or there are other good choices. Modified half shafts are needed. I'll try and post some pictures of my project

The cobra irs has some issues that can be easily fixed. The assembly is contained in a frame assembly that space permitting can be installed easier than most.

My limited experience has shown that a live axle is much easier to load and tune for drag strip, high traction situations. Irs would typically be used, not for straight line, but for road racing applications.

My 2 cents

Ron S
01-28-2009, 03:15 AM
If you were never to use sticky tires,high HP motors or cars weighing over 3000 pounds I'd agree that the IRS set ups would work well.Most of the cars here are street cars,that get pounded on{lots of holeshots}I don't know of an affordable IRS that will be durable enough to put up with what I do to my cars.I'm sure you could spend thousands and thousands of dollars on good half shafts and beefed up center and still be spanked by a guy with a properly set up straight axle.I'm a firm beleiver in keep it simple stupid,durability always seems to go with that saying.Just my 2 cents.Ron

wicked68
02-01-2009, 05:42 PM
dont be surprised if you get a lot of wheel hop with an irs

I have seen several late model cars running this that get nasty wheel hop under power in the first 200 feet.

newby
03-29-2009, 01:37 PM
these open ended comparisons never work... there are too many possibilities.

for solid axle set ups there must be a dozen routes to go with varying degrees of fabrication required and their own pros-cons... from traditional 4 links to truck arm conversions to slapper bars to dse quadralink style set ups the list goes on and on.

for IRS you have just as many set ups... jag, ford mustang, crown vics and t birds, vettes, vipers, bmws, new gto's, porsche, custom 9", some newer suvs, home built and the list goes on.

when considering which route you want to go, you must decide on two things: how much do you want to spend and what do you HONESTLY plan to do with the car. if you plan to street drive and long trip the car, IRS without a doubt.

if you are not a member of your local scca club and the only venue you have for 100 miles is a drag strip then solid axle is probably the choice for you.

i would say that if you are north of 800ftlbs or your car is particularly heavy, solid axle all the way. however, if you have the money to build a reliable engine that puts out greater than 800ft/lbs of tq (which is coincidentally the max for most OEM IRS) then you probably have the money to modify any IRS to handle the power any way.

look at what the OEMs are doing. all of your 'top notch cars' are irs. the cars I most enjoy driving on the street all have IRS. Unless you live on the west coast, all roads are bumpy. I've had old ass solid axle cars that could pull a posted 45mph clover leaf on/off ramp at 60mph with no drama, but as soon as I hit a break in the pavement is was tokyo drift time. that craps gets old.

c4 irs and some others are different than say the c5/c6 that a previous poster bashed in that they are essentially 4 links. most ppl agree the gto and cobra rears make too many compromises and are not worth messing with. in europe people constantly rip the rears out of bmws for their own irs projects with great success. viper rears are pricey, vette rears will set you back around a grand, and most of your 'engineered' set ups will set you back at least that.

further more I would pay money to see ANY car launch well with 500+lbs/ft of tq and super hard super low profile run flat street tires that come stock on the vette... lack of traction does not constitute a design flaw.

if you want to get a real comparison your question needs to go more like: "...I have $2k to drop on getting a complete rear end in my car. I have a decent locker posi 12 bolt with drums under the car now, but I found a good deal on a dana 44 c4 rear. what are my options for the 12 bolt and which would you choose and why?"

Prechel
10-31-2009, 07:05 PM
i think a good question to ask would be who bought the 69 camaro from century 21 that had the c5 vette IRS swaped into it how did that turn out for the man who bought it what kinda problems did he run into if any

Monte71
11-02-2009, 01:36 AM
i prefer live axle,but if IRS wasnt so expensive id prolly switch,and if it can handle 1200hp.

Norm Peterson
11-03-2009, 08:34 AM
these open ended comparisons never work... there are too many possibilities.

<snip>

when considering which route you want to go, you must decide on two things: how much do you want to spend and what do you HONESTLY plan to do with the car. if you plan to street drive and long trip the car, IRS without a doubt.

if you are not a member of your local scca club and the only venue you have for 100 miles is a drag strip then solid axle is probably the choice for you.
I don't think the answer to the question of which suspension to use for street/trip/SCCA activity usage is anywhere near that absolute. For dragstrip duty it probably is.


Perhaps the questions for a typical PT car that should be asked are "by how much will the ride improve by swapping in IRS assuming that currently achievable stick axle suspension performance levels can at least be maintaind for each individual's specific driving?" and "after I get it done, will I think it was worth it?". Anybody else feel that a car that fails the second question will end up being sold?


Norm

Jim Nilsen
11-08-2009, 07:06 PM
So far I am satisfied with my C4 IRS and front suspension. The car handles like a go kart. The corners have been really predictable and when it breaks loose it hooks right back up. The looks of the IRS is something you don't get with a straight axle. The ability to change camber is also a nice option although you can spend a lot of money and do the same with the right straight axle. I still haven't gotten on it hard enough to get wheel hop but we will see if it happens?

All in all it is what you like and then what the car likes for the way you have the rest of it setup, too much power and the IRS just isn't up to the task.

I built my rear frame so that I can put in a straight axle setup with ease and if I ever get too much power I may change it then. I paid $650 for my Dana 44 rear with the brakes and that is hard to beat.

van454
11-13-2009, 04:12 PM
I have had a bit of look at the IRS from the VE commodore (pontiac G8) and it looks like a very well engineered set up. It is all on a nice sub frame too, shouldn't be too hard to fit one to another car. Maybe that would be a good option for my third gen T/A

calforniacuda
11-14-2009, 09:46 AM
I think the cheapest and easiest IRS setup to put in another vehicle is from the Mustang Cobras. You can get a used entire system for under a $1000. There are lots of aftermarket kits to stop wheel hop. Anthing else needed like coilovers, bushings, sway bars, etc. The sytem fits into a cradel that was bolted into Mustang rear end.

pdq67
11-27-2009, 06:18 PM
Reading right along.

pdq67

Norm Peterson
11-30-2009, 07:06 AM
I think the cheapest and easiest IRS setup to put in another vehicle is from the Mustang Cobras. You can get a used entire system for under a $1000. There are lots of aftermarket kits to stop wheel hop. Anthing else needed like coilovers, bushings, sway bars, etc. The sytem fits into a cradel that was bolted into Mustang rear end.
At one point, I had a 3-D suspension spreadsheet that was based on this particular IRS. Damned if I can find it now, though.


Norm

killer67
01-27-2010, 12:36 AM
Full chassis and independent is the way to go

BillyShope
01-27-2010, 04:31 AM
...and has recently (within the last couple of days) been updated to take into account the unequal dynamic spring forces when antisquat is not 100%.
http://home.earthlink.net/~whshope (http://home.earthlink.net/%7Ewhshope)
over 130,000 visitors
Since "killer67" has revived this old thread, I have the opportunity to correct a comment I made earlier. Since, with complete cancellation of the driveshaft torque, there is no chassis roll, the relative values of front and rear roll stiffness have no effect and the spreadsheet change I mention above should not have been made. I have again corrected the spreadsheet on Page 18 and it is now in agreement with the spreadsheet on Page 40. In other words, if you calculate the distance forward to the instant center from Page 18 and input it into Page 40, you get the same results (i.e., identical angles for the symmetrical links.)
http://www.racetec.cc/shope

Norm Peterson
01-27-2010, 04:36 AM
Full chassis and independent is the way to go
If it were only that simple. Please read at least the first page of this topic.

"Full chassis" is kind of vague.

Anything as "one-off" as swapping an IRS into most any stick axle car is going to require some development. Unless, I guess, the car only gets used for easy cruising and/or static display at car shows and the IRS is simply a "bragging point".

At some risk of repeating myself within this thread, a well done stick asle suspension is better than in indifferently done IRS (and vastly better than a poorly done one).


Norm

monteboy84
01-27-2010, 06:38 AM
The old IMSA GTO class allowed only stick axle rear suspension on cars like Camaro and Mustangs, but Corvettes could run independent of any kind, (quick change center section) or a solid axle. The DeAtley team with David Hobbs driving, switched from Camaros to Corvettes, they were winning with the Camaros, the Corvettes with independent suspension didn't work very well, they wore out the rear tires early in the race, traction out of corners late in the race was a huge concern for those cars. They eventually got the cars working better, enough to quit running the Camaros they had, but there was little difference between them on a race track.
Perhaps some other application/situation would show up differently.

It's funny you mention that, I'm sure what you were running against was all C4 stuff, but all the geometry of our C3 race car is terrible. It's got a huge amount of bumpsteer due to the trailing arm/halfshaft arrangement, which means the best setup has a bunch of static toe-in out back. There are things we've done to alleviate this and make it a good track car, but for street use it'd be pathetic. I'd rather have a straight 9", which is what we have in the Camaro.

So, an IRS will get you worse off if it's not properly designed, I'd say for the majority of PT guys, a good solid axle is a better arrangement.

79-TA
01-27-2010, 01:37 PM
If it were only that simple. Please read at least the first page of this topic.

"Full chassis" is kind of vague.

Anything as "one-off" as swapping an IRS into most any stick axle car is going to require some development. Unless, I guess, the car only gets used for easy cruising and/or static display at car shows and the IRS is simply a "bragging point".

At some risk of repeating myself within this thread, a well done stick asle suspension is better than in indifferently done IRS (and vastly better than a poorly done one).


Norm


You'll notice that he (killer67) left about 50 other equally insightful posts in the course of 2 hours last night.

Norm Peterson
01-27-2010, 02:07 PM
Yup.

I looked there too, as it was too suspicious-looking to not provoke curiosity.


Norm

brian65fb
02-11-2010, 02:29 PM
griggs racing mustangs seem to be fairly quick on a road corse and they use a solid axle with a torque arm, nascar uses the truck arm setup Hot Rods To Hell sells a kit for 67-81 camaros