Self-contained IRS?

The Infiniti/Nissan unit is nice because it's all aluminum, has a huge aftermarket, and very strong diffs/axles with several ratio options. It's not completely self-contained though. Just need an upper spring perch and upper shock mount. It's easily converted to coilovers using the shock mount. Good modern brakes. And four big ol 14mm bolts hold the whole thing in.

But the biggest advantage right now is price and availability. While 350z's stay valuable, G35's have hit the bottom of their depreciation curve. There are at least 10 at my local Pull-A-Part at any given time. And running donors are sometimes dipping below $1000.

I had along post here and Android/Chrome ate it.  Will post later when I am home and on a real computer instead of a toy.

Most cars with IRS have bolt-inable setups because that is what works best on an assembly line.  I knew someone who threw an MN12 rearend under a '57 Chevy pickup, and all it required were four brackets for the subframe and two for the springs.  He pulled the hubs and had them redrilled to 5x4.5 to match the setup he had in the front.

Frenchy is right on this. 

The Jaguar IRS is the only completely self contained package I can think of (including the suspension mount points)

(I just bought one one for my El Camino street rod project)

In reply to SVreX :

It's also garbage, in ways that I posted in the treatise that I'd started to post but got lost.  There a lot of geometrical as well as practical reasons why using the axle as the upper link is a bad move.

The Jag rear is very good at not taking up much space, which is great for its original applications.

In reply to Knurled. :

Well, teach me. Before I do something bad. 

In reply to Knurled. :

You are saying the geometry is terrible. Frenchy is saying it can be adjusted to just about anything. 

Mixed messages. 

frenchyd said:

pres589 (djronnebaum) said:

Doesn't the Jag setup use the half shafts as the upper suspension member like a C3 Vette? This has a bunch of force channel through the diff / spider gears. 

Yes!?! Your point?  Geometry wise it can be adjusted to whatever your requirements are. If you are worried about strength, it is capable of dealing with massive forces and I’ve seen it under more than a few pickups. The big Jaguar sedan weighs over 4600 pounds. Add 4 fat old duffers and golf clubs and it still holds up.  ( by the way the parts are basically the same in the big sedan or light XKE, including the needle bearings to ensure accurate alignment that most rubber bushings don’t.  

Compromised geometry is the point.  

Making a live axle work better is easier than that thing.

It's great for the people who want IRS for the sake of IRS.  It's a heck of a lot of work to make that work better than IRS- don't underestimate the amount of work that Group 44 put into that to make it work.  There's a reason that the DB7 never raced, when the later V12's did, with a less compromised IRS in it.

SVreX said:

 

Frenchy is right on this. 

The Jaguar IRS is the only completely self contained package I can think of (including the suspension mount points)

 

(I just bought one one for my El Camino street rod project)

If all you want is IRS for the sake of having IRS, that's a great package.

If you want to tune it to the Nth degree, it's not so good.  

I didnt read the thread but I think the IRS is far to big to ever be self contained. That's why we should just go to a flat tax.

Sorry, just a bad joke. No actual politics here. Go back to Jaguar bits.

In reply to alfadriver :

Yes. That I understand. 

The question in this thread was about packaging. 

My personal question is about street rod applications. I don't think most street rod rear ends are tuned to the Nth degree. 

Street rods are looking for strength, some improvement over stock, and yes sometimes it’s appearance or “for the sake of it”. They are not  usually built to handle to tight tolerances (especially in a 4000 lb vehicle)

But I am trying to learn. What’s your opinion in street rod applications?

In reply to alfadriver :

I don’t think I can agree with that statement.  Perhaps because of my familiarity with that suspension it’s realitively straight forward in ways to improve the handling.  Both as a DIY and if you just want to buy the parts and bolt them on.  

For the later go to Rob Beere Racing and you’ll find the pieces and parts, For DIY there are plenty of examples Not just Group 44 also Huffaker racing,  Lister,  Walkinshaw Group A,  etc.  

plus further examples by following hot riders and Kit car builders. 

In reply to frenchyd :

From a handling and racing standpoint, I would never take any examples from hot rodders and kit cars.  In the almost 20 years I raced, I never saw ether (other than the live axle Factory 5 cars).

But you are welcome to disagree.  Having seen one in action, and how one had to tie it to the car to make it work- no thanks.  Good if you may have racing budgets to make it work, but if not, find a better solution.

IMHO, making a live axle work better would be a whole lot easier and cheaper.  Given that suspension design is free in DM and EM, one should compare the number of IRS vs. the Jag IRS vs. live axle set ups.  From what people have posted, the live axle dominates those two classes.

Again, if the goal is to just have an IRS, it's a great choice.  If you want really great handling, well, not so much- unless you put in a lot of work.  And you can put the same amount of work in other choices and get better results.

SVreX said:

In reply to alfadriver :

Yes. That I understand. 

The question in this thread was about packaging. 

My personal question is about street rod applications. I don't think most street rod rear ends are tuned to the Nth degree. 

Street rods are looking for strength, some improvement over stock, and yes sometimes it’s appearance or “for the sake of it”. They are not  usually built to handle to tight tolerances (especially in a 4000 lb vehicle)

But I am trying to learn. What’s your opinion in street rod applications?

For a street rod, I'd go with a live axle.  All day long.  3 trailing plus one panahard, and you are all set.  And the ultimate strength potential is better with the live axle choices.

If you want IRS for the sake of having it, it's not a bad choice.  But when I read the opening line- given that the starting point was the Grassroots prototype car, well, I figured ultimate handing was very high on the compromise list.

In reply to SVreX :  That rear end looks very nice, looks like it’s been rebuilt!

What the street Rodders  do is show alternative methods.  For example the stock Jaguar uses trailing links to handle the bending that occurs under acceleration  ( the tires want to toe out under hard acceleration without the trailing links ) 

the problem is the arch that the trailing links proscribe conflicts with the arch of the suspension as it moves up and down.  Jaguar gets away with that conflict by mounting the trailing arms in rubber and hanging the whole  cage on rubber.  

If you strengthen up the lower wishbones enough you don’t need the trailing links, or you can tie the trailing link inward to align with the inner pivot.  

I could show you pictures of your choices  if I ever figure how to post links.  There is a whole segment today on a article about Lister, including the rather clever way Bob Knodt  dealt with the issue on his track car.  

Bottom line? For a pure race car Ridgely mount the whole assembly. For any street use the factory rubber mounts. For a combination of each use the polyurethane mounts in approximately the stock position.  

Shocks, springs, and swaybars  are pretty well set for you by using the combination the factory settled on based on weight and intended ride.  

Example around 4600 pounds use the springs, shocks, and swaybar package in the XJ12  

around 4200 pounds with a little sportier ride select the XJS 

Around  3500 pounds use the XKE V12 2+2 

Around 3000 pounds use the XKE V12 roadster 

around 2700 pounds use the XKE ROADSTER up to 1971  

In reply to alfadriver :

What a straight axle lacks is exactly why cars went to Independent front suspension in the first place. That is any bump, force, or load applied to one wheel causes the opposite wheel to react in a negative fashion. 

Yes circle track guys get around  the problems of a straight rear axle with all sorts of trickery ( most of which NASCAR has outlawed) 

F1, Indy cars,  heck any race car that allows IRS quickly goes to it because they’ve already figured out how to make it work. 

Now I’ll grant that if you are putting 9000 horsepower to some great big floppy slicks that act like caterpillar treads IRS doesn’t get you anything

What you gain with IRS is the same thing you gain with IFS. That camber curve can be altered on front and rear suspension to gain traction as the car rolls over.  It’s done the same way, unequal length links. Usually one  link will be shorter than the other link.   If you look on a Jaguar the upper link is the axle and it’s length  is fixed (?but it can be adjusted). however the lower link is easy to make adjustable to adapt to different roll centers.  ( even if stock factory pieces are required. 

For  road racing  a well designed IRS is best. 

In reply to frenchyd :

That picture is not mine. It’s just an internet picture. 

The stock setup in the XJS mine came out of did not use rubber mounts for the carrier. It had metal clips that secured it to the frame arches directly. 

In reply to SVreX :

Go to Moss Motors’s Jaguar site look for the mounts. 

Heck let me find it for you.  

OK I’m bad, they are still using XKs unlimited site. 

you’re looking for suspension& steering, rear suspension. 

Part number SKU:JACAC  3067 

4 required 

 there are also pictures of the trailing arm bushings.  If you have access to a junk car you can chisel the mount off there are 4 rivets holding it on or if you want check Matin Robbey’s site And buy new. 

Lexus SC300 rear IRS subframe holds everything except the upper coilover mount. 

LSD options are limited (and not cheap) but you can swap the diff for a MKIV Supra TT diff. Bolt in swap, but one of the axles has to get swapped as well. (Supra diff is bigger on one side requiring a shorter axle.

Lexus parts are super cheap though. 

I have no clue about the geometry though.