Straight Axle or IRS & Which One
 

I'll start with my understanding of the subject, and let you all tell me where I'm wrong. I need some education.

IRS will give better handling and ride, if only theoretically, but this seems to be accepted by most. Many manufactures offer straight axles, especially the 9" Ford. Certainly they can work. The very short (approximately a foot) drive shaft limits the allowable travel on a straight axle, which can affect handling and ride. Maybe this is true, but in a practical sense, does it matter?

If you go straight axle there is three link and 4 link and maybe more. Handling issues that I'm certain that I do not understand. I do know that a 9" is plenty strong for 500 lb-ft of engine torque and sticky tires.

IRS - most manufactures who offer these use the T-bird 8.8" setup. A FFR guy at the London show stated to me that with street tires the HP does not matter, as you cannot put more to the ground than the 8.8" IRS can handle. I don't buy that argument, as I put a 283 with turbo 350 automatic in a Vega, leaving the Vega rear end and stock tires on it, with the same reasoning. First time it shifted from 1st to 2nd at full throttle the rear end disintegrated, and the engine over revved and spun a bunch of bearings. Chock it up to youth.

The Jaguar IRS is used by a few and is plenty strong, but a pain in the butt to work on. At least that is the claim. Mercedes, and Vettes have better IRS on them, but I hear little about them. I don't know why you couldn't cut a 9” down and make an IRS out of it. What options are there on IRS?

Is there any info on how much torque the different IRS options can handle? Any practical information on the ride and handling advantages on the IRS?

Thanks in advance.

Since the IRS control arms can be set up just like an independent front suspension, it can be manipulated to keep more tire contact at more angles than a straight axle unit can be.
With the proper geometry, it can also be manipulated to increase corner turn in toe and camber, which can be very important on road tracks- not so much for drag racing or street. Since there is less unsprung weight, road manners are also better, especially on rough roads.

The 8.8" Ford is a very nice IRS to use and work with, but many others are available that can work equally well. I believe the Jag Rears are available with outboard rear ends on some kits. The Everett Morrison takes Vette suspension, including IRS IIRC. Some kits are available with Ford 9" adapted IRS set ups and several aftermarket companies make 9" Ford IRS set ups for many applications, but I'm not aware of any distinctly made for a Cobra. However, anything can be made to fit with enough work.

Most IRS can be made to handle substantial amounts of HP/Torque with the proper hardened and machined axles. Several aftermarket shops make high torque rated axles/CV's for the 8.8 Ford IRS as well as the 9" Ford IRS units.

Try www.dutchmanaxles.com for one place for 9" Ford IRS set ups and custom, race rated axles. Very nice work, good people to deal with, and very good service. AMP also offers these pieces but their reputation for service is somewhat "lacking".

If anyone is looking for one, I happen to know where a Jag Rear and front suspension out of a Contemporary is available at the moment. Includes Wilwood brakes, inboard brakes in rear, and all the suspension pieces.

Bob

package IRS assemblies...
 

Team321 (www.team321.com) in Cocoa Beach, FL makes a double a-arm,
rocker arm IRS using an 8.8" diff. It can be supplied in custom widths for various
applications and there are a number of brake options available for it. There are
several photos on the site of an FFR chassis that was modified to take this IRS.
RCC Specialty
Products in Ft. Worth, TX makes a 9" based package IRS using Toronado half-shafts and hubs which they say is good for 650 hp. Your choice of
inboard or outboard brakes. Although the site doesn't mention available widths,
I assume they can supply it in various widths.


....Fred

AMP also make a good IRS. They use a modified 9" and it is supposed to be much stronger than the Jag Salsbury.
http://www.cobracountry.com/amp/home.html
John

We run Vette IRS but we also use the Vette frame so just a natural. It is a great unit and the Dana 44 has been around for years so pretty much figured out and proven to point of perfection. Same unit used from 1968 until 1980 when they went to an alum housing but still interchangeable internals and so on. Also since its years of being raced and marketed there are many aftermarket parts avail;able. The fact they are the 3rd generation Vette and they are now selling Gen 5 Vette makes them very affordable. The street rod guys go after the gen 4 stuff so again more availability to gen 3 stuff. The G4 items were lighter sprung weight but aftermarket g3 is also reduced weight so there ya go.
The G3 car was in the 3700 pound range so pretty beefy, I have never grenaded a rebuilt C3 IRS even with very healthy big blocks. I have broken one 1/2 shaft U-joint but that happened at low speed/RPM so almost no damage. I do recommend Hoops for all drive shafts in any car used as a TOY. Lack of traction probably saved all my cars from IRS damage but they are not drag cars and a big block in one of these will just roast tires regardless. I do think they get better traction than most IRS units out there because of the design. They seem to squat N squirt as only way to describe launch.

Depends
 

Hi,
1st off you or me could never drive our cobra's on the street fast enough to warrant an independant rear end. choice is another matter.
2nd if you want to track the car, you do what you want to do; drags are only for a built 9" Ford, NHRA doesn't allow IRS in faster cars. Road racing is IRS, but then you better have a full roll cage and fuel safe cell or your toast.
3rd, a show car has just too much money thrown at it and do whatever turns your crank.
HAVE FUN with your COBRA.
Perry.:MECOOL:

What I'm doing for my 8.8 IRS build is using the 31 spline differential from a 2004 Mustang SVT. Standard 8.8 is 28 spline. Ford made the switch for their higher horsepower Mustang. Custom axles have to made but the are available from a couple manufacturers like Dutchman.
Larry

Without an IRS setup on a 90" (Cobra) wheelbase car with any kind of HP, it'll swap ends faster than you can blink an eye. Also, with a short driveshaft you'll have a tendancy to bind up the rear with a soft setup on a straight rear. Food for thought.

Olddog,

You are in the mid-West so it may not be the same however, New England roads are better managed with IRS. Solid axle light cars tend to skip on rut filled roads and pavement variations in corners. I can say one ride through Boston with a solid axle car will make even the most die hard solid axle man question his choice.
IRS sticks and skipping is of no concern............I have done it both ways....

My 2 cents,
Jeff:o

Here is some REAL food to digest.
Colin's Pro-street legal cobra is now into the 7's in the 1/4 mile,nuff said about a solid 9" rear.[ 1,400 HP ]
My slow smogger cobra with a solid 9" ,tri bar 4 link and 8 1/2" driveshaft has been to California 3 times,Idaho,Nevada, Oregon coast 2 times and regularly sees friday night street drags @ 11.9's. All you need is a little knowlage of how to set up suspensions and you can have a real solid road cobra.
Actually the driver determines if you spin out,I know,try going over 'Snow'qualmie Pass with a cobra in the snow.It was a fun adventure.
Perry.

So guys,
Is there a consensus opinion/formula about the best way to set up a solid rear axle for good hookup as well as sticky cornering, does it truly have to be one or the other (hookup vs. handling)? There has to be a way to keep the suspension "at balance" to allow good performance both directions...

Yes. It's called smooth pavement.

OLDDOG = "There has to be a way to keep the suspension "at balance" to allow good performance both directions..."
No it does not have to be 1 or the other but a compromise is giving a little here to get a little there and nothing wrong with that.
Highplains is much more inspired to the drag side and he is right in claim Advanced ET cars must have a solid axle and dis-allows IRS but that alone does not make it a bad choice for a Cobra, Vette or other performance suspension.
As a point of reference the Olds Toranado mentioned earlier is an absolute torque monster and a real tank (very heavy) it has a non solid axle. I agree not apples to apples here but a paralell theory ...kinda?
If I was building a drag car it would have a solid non sprung axle and my Cobra inspired cars have an IRS but that just means I won't be stealing highplains extra parts and visa versa so life is good