2nd Gen IRS

[exwestracer]

So does that mean you're going with a custom front end? It would be a huge coincidence if those geometries lines up with something that's already out there! I asked Detroit Speed for their front end geometry once to design an IRS, but they said no. Completely understandable, but it would have been cool to design something complimentary.

A little info on how I try to have the students approach a project like this...

We always start a project like this by establishing the lower control arm level in in both planes, then the upper arm mount is located to give the swing arm length to work with whatever tire is going on the project (lower profile= less camber gain). This is all done on the "concrete computer" - drawn out full size on the floor. We will also do the same for the 350Z rear and map out the swing arm length and R/C progression to compare that with the front.

Lastly we look at projected front/rear weight balance and C/G heights (admittedly this is usually an educated guess given engine type, fuel placement, etc.) to come up with an idea of front and rear roll moments and front anti-dive geometry. If we have time (and all the components), we'll weigh the car and do F/R tilt and side tilt weights just to verify our assumptions. Very rarely do we get that far given the time available and the emphasis on learning, not production.

This one is getting a 2X4 rectangular frame, Howe replacement lower control arms, coilovers, and SPC adjustable upper arms. We will be building all the mounts to fit the desired tire size, ride height and geometry.

[zamora7]

Just something else to throw out there: The new GTO rears are not a double A-arm setup but they work really well, are very well packaged, and you can buy the whole setup brake-to-brake all day long for $250 on Ebay. You have very limited gear selection and posi units but they come with 3:45 gears and posi-traction from the factory designed to work in a 400 horse, 3800 lb. car so they do hold up fairly well. If you make more power we (and other companies) offer billet 300M CV shafts and stubs and there is even a company now making Ford 8.8" retrofit diff kits. For $250, you could buy a couple of spares!

Damn! This is what first came to my mind when I saw the title of the thread, any idea how difficult would a set-up like this would be? I even thought of putting one of these into a 4th gen fbody, but money is the only issue.

[exwestracer]

Damn! This is what first came to my mind when I saw the title of the thread, any idea how difficult would a set-up like this would be? I even thought of putting one of these into a 4th gen fbody, but money is the only issue.

The GTO uses a semi-trailing arm suspension which is great for packaging (lots of rear seat room), but is always going to be a compromise when it comes to handling. The STA design has a very short swing arm length, and the angled mounts give caster, camber and toe change as the suspension travels. These things have been around for years in everything from Datsun 510s to BMW 850s (...so that's 340 cars...? lol). If you're going to go to the trouble of swapping one into another car, IMO the only reason to choose that design is for interior space reasons... There are much better packages out there.

[zamora7]

The GTO uses a semi-trailing arm suspension which is great for packaging (lots of rear seat room), but is always going to be a compromise when it comes to handling. The STA design has a very short swing arm length, and the angled mounts give caster, camber and toe change as the suspension travels. These things have been around for years in everything from Datsun 510s to BMW 850s (...so that's 340 cars...? lol). If you're going to go to the trouble of swapping one into another car, IMO the only reason to choose that design is for interior space reasons... There are much better packages out there.

Good to know this, thanks for the info.
340 cars lol.

[exwestracer]

Well, we HAD photos...until Ryan's camera vanished out of the shop last week. GRRR...

The frame rails are laid out and tacked together, and the frame has been fitted into the floor. The guys are about 1/2 way through building the mounts to hang the IRS cradle. We are using heavy wall DOM tubing to make pins to go through the stock subframe mount bushings. Ryan can replace the bushings with solid later if he feels the need. The pins are welded into bosses off the frame, and internally threaded for cap screws to hold the cradle up. We may put some double shear plates on the front mounts just as a security blanket.

Once the rear cradle is in place, the next big job is to get the front arm mounts located and built. The Howe front LCAs are late (surprise!) getting here, so the front may get mocked up with the stock lowers (same geometry, he'll just need to use spacers for the Heim joints on the Howe arms).

Ryan was understandably PO'd about losing the camera, but he did take some cell pics Sat night, so he may post them. If not, I'll try to get a few before the frame goes in the car.

[exwestracer]

Some progress on the 350Z IRS installation. The Howe LCAs showed up today, and they're pretty disappointing... They advertise them as an OEM replacement, even specify the C/C length, and yet they're an inch shorter than the stock arms. Good thing we didn't have the front mounts on yet! The 2 arms aren't even the same as each other...but they'll work. The guys got the front crossmember placed tonight after I took these photos. We're using 2" X .120 DOM to build a "K" member that will pick up the LCA and motor mounts.

The rear cradle mounts are tacked in place, enough so it will hang on it's own bolts. The fronts will be boxed, and there will be some gussets added at all corners later. Hopefully, we'll get the front control arm mounts on and get this thing stuffed up under the body in the next couple of days.

[jp455]

Looking good! Whats the deal with the gigantic spring pocket though??

[exwestracer]

Looking good! Whats the deal with the gigantic spring pocket though??

Stock coil spring mount for the350Z. To save interior space, Nissan separated the spring and shock. You can just see the shock eye bosses on the top of the uprights. We had considered using those pockets...for about 10 seconds:bsjerk:... Since he won't need the spring perches, those bulky transverse links are going to be replaced with coilovers and straight tubes later.

[Macadoo355]

I have a bunch of pictures on my phone ill try to swap to the computer tonight, thanks guys

[jp455]

I figured they are the coil spring mount, they just look like the spring has a huge diameter! Good deal that you're getting rid of them, it looks like something a lot smaller and lighter can be substituted.

[exwestracer]

Well, a last update (from me anyway) on the 79 Camaro IRS project. The car is returning home and hopefully will be completed in good time.

Ryan has a few more detailed photos he may share.

The front K member was completed and we designed some innovative upper control arm mounts that mount to the large surface of the inside of the rail, rather than the top. There wasn't time to get the upper mounts for the coilovers built. The body was lowered onto the frame and everything fit together remarkably well. Getting the aluminum IRS cradle to fit for proper ride height required cutting about 1/2 of the rear seat bulkhead out, but the clearances were pretty close. If the cradle had been steel it would have been much easier for Ryan to modify it than cut more floor. Also, the decision to include a full frame welded into the floor probably took up a good week of our limited build time. I believe it was the correct way to go structurally, but the swap could be done much more easily by modifying the IRS cradle and stock rear subframe.

We ended up with a swing arm length of about 2X track width in front, which should be acceptable for the fairly low profile tires he is going to use. The rear is similar, and while we obviously did not get around to checking CG, I think the front and rear geometries will complement each other.

The car left rolling, which was a major accomplishment given that only 2 students did all the work. I hope Ryan will keep us all updated on progress and results.

[jp455]

Whatever happened to this project? Any pics of the end result? Would be awesome to see how it takes a curve!

[overZealous1]

attepting it in a 67 camaro next. will start another thread. these rear ends are getting plentiful and cheap!