Rear Frame Design

[olason]

I am modeling a frame for my 1968 olds 442. I used approximate measurements, and built the frame thus far similar to the photos of an Art Morrison chassis. I am doing all of this on Pro Engineer WF 4.0, so changes are much easier to do now. I was wondering why I had the bent rails in there being I plan to run an IRS, and the pictures had a solid axle used.

What would be the best way to design the rear frame for strength? I want to have a rear sub-frame that I can drop out for easy removal of the center housing. I assume using straight-cut edges on the tubes in the rear would make for the easiest mounting of a sub-frame. I should have to worry about the strength of a sub-frame I don't believe. Would it be possible to even use one from a C6 Corvette since I plan on running C6 suspension.

By the way I have C6 spindles, hub, rotor, etc. I found someone had posted on the gt40s website.

From what is below I already plan to redesign it, but I wanted some input.

[exwestracer]

I am modeling a frame for my 1968 olds 442. I used approximate measurements, and built the frame thus far similar to the photos of an Art Morrison chassis. I am doing all of this on Pro Engineer WF 4.0, so changes are much easier to do now. I was wondering why I had the bent rails in there being I plan to run an IRS, and the pictures had a solid axle used.

What would be the best way to design the rear frame for strength? I want to have a rear sub-frame that I can drop out for easy removal of the center housing. I assume using straight-cut edges on the tubes in the rear would make for the easiest mounting of a sub-frame. I should have to worry about the strength of a sub-frame I don't believe. Would it be possible to even use one from a C6 Corvette since I plan on running C6 suspension.

By the way I have C6 spindles, hub, rotor, etc. I found someone had posted on the gt40s website.

From what is below I already plan to redesign it, but I wanted some input.

Think carefully about how much kick-up you really need with IRS... You have a much smaller shaft size and less motion than what you'd have with a stick axle.

[RS_Customs]

Another thing to consider is the radius of the bends in the rails. There are only a few companies out there that will bend rails for you and they usually only have a few die sizes to bend with. You could probably call around and find out what they have so you can use that in your design before you get to far with it.

The nice thing about designing a IRS rear is you can make a subframe to help with strength.

Robert

[T.K.]

Have you checked out roadser shop IRS setup. It uses C6 control arms and spindles but a 9" drop out center section. they sell it complete, but I bet if you wanted it minus the control arms etc they could price it for you. Its steep but after you see what it will cost to have 2x4 bent, maybe not so bad. If nothing else you can see that it really doesnt kick up much at all and get some ideas of what it should look like. like stated above its really not all that similar. You change your mind and want a straight axle 9", I'm considering selling my whole Art Morrison setup

[RS Performance]

T.K. is correct - we offer our IRS rear as a standalone unit to allow builders to integrate it into a chassis.
http://www.roadstershop.com/products...dent-rear-unit

It is really designed to work as a 'unit' as the control arms are actually our own and designed with certain geometry to achieve the specs offered by the setup. (It does use the C6 spindles and hubs.)

We also offer it separately to eliminate the 'guesswork' for those looking for an IRS. We spent a great deal of time and effort in not only the R&D of the setup, but the real world track and street testing to ensure it actually works!

Also check out the video here, which highlights the benefits : http://roadstershop.com/blog/2011/ro...-irs-overview/

If you have any questions on the setup, just let me know!

[T.K.]

man i knew the spindles were c6, whiffed on the CAs

[olason]

Hey thanks for the responses,

I haven't had time to be on here much recently, or work on my project car.

I knew that roadster shop had that rear assembly. How hard would it be to modify to use with an 8.8" irs unit? That is what i planned to use out back on this car for now.

This project is in on the back burner for now. I got my senior design project, and we compete at the end of April in new Hampshire for sae formula hybrid. The frame isn't even complete yet from the last group. So there is a long way to go. I will contact roadster shop about this as a possibility though

[Oldskool442]

The 8.8 unit is definitely an option, and they can be found in several cars other than the 99-04 Cobras. If memory serves me right, Thunderbirds had them in iron and Lincoln Mark VIIIs had them in aluminum, and they're cheap/plentiful in the junkyards. The 01-04 Cobras and 00 Cobra Rs were the only ones that had 31 spline, but the diff can be swapped out to fix that. If you use the wheel bearings and hubs from these cars you might be able to run the OEM axles, or find an aftermarket company to make custom length if necessary. There's also a couple companies making a rugged diff cover to replace the flimsy factory units.

Take a look at the 99-04 Cobra subframes too, it might be a good option for mounting the LCAs to, and mount the UCAs and diff to the chassis itself.

[Rhino]

Keep in mind many suv's have them as well. Later years of the Ford Explorer/Mercury Mountaineer had an 8.8 and IRS. They're likely steel so it's a cost/weight trade off, but at least it's 100% sprung weight on the "right" end.
If I recall correctly the mountaineer almost always came with larger spline axles and some sort of limited slip unit.

[T.K.]

i dont know of anyone selling a unit that uses the 8.8. if you still have the donor i have two suggestions for you. 1) build your frame to accept the entire rear subframe if possible, or 2) after pulling all of the IRS parts from the donor make a jig that bolts to all the IRS pickup points. use the measurements of off the jig to do your cad magic but more importantly use the jig when you build your frame to maintain the OEM geometry