The number of mounts really doesn't matter as long as the differential is solidly mounted and that there is sufficient leverage to eliminate flex in the mounting system in relation to body role.  What I am saying is that you want a mount that is solid but you also what a mount that connects the differential out towards the sides of car to eliminate differential flex in relation to body role.  If you look at the corvette units they use the bat wing, the Jag unit uses the cage and even the ford units in their stock configuration have the mounts spread out.  I guess my question is what will be your mounting configuration as far as design??  that is really more important than the number of mounts.  BTW WELCOME TO THE FORUM!!!  Got any pix of your project???

Schitzo! How you go?
I had to take time to think about your question. And I had came up with the same as these guys. Looking at PJ's pic it also had dawned on me. Chevy was pretty smart with their mounting points by moving them outward, the further the mounts are moved away like that. The less motion the carrier will have moving in relation to the rubber mounting.  Your 8.8 mounts closely to the differential no? Can you post some real (your) pics?

Did you find my post, "First drive C4 conversion in a BMW". It's in the IRS video thread. Video shows a Corvette C4 in a E30. He also removes the C4 leaf spring and opts for coilovers.

Last edited by Ralphy (12/26/2011 6:36 am)

Below are some pictures of the subframe and diff itself. It will have 2 mounts on the front and two in the back. There is still quite a bit of fabrication I need to do but at least I have completed the design which was the harder part.

This was the day I got the diff and put the two together to see if it would even work.


Initially I was going to use a steel bracket bolted to the aluminum cover as the rear mount but I really didn't like it from a strength/function standpoint. So back to the drawing board.


After some thought I chose to drop the aluminum cover and use a steel offroad cover. I will weld arms that stretch from the cover to the rear mounts

Last edited by Schitzo (10/29/2012 7:11 pm)

Schitzo,
I think the important issue is, how much are your control arms moving? Your sub-frame is where your suspension is mounted. If your priority is handling,, stiffer mounts are the way to go. Your control arm bushings should be changed also.

Ralphy

Last edited by Ralphy (12/26/2011 6:00 pm)

I like your steel cover idea, just make sure it mounts as far out in the sub frame as possible for better leverage.  I like redundancy so if you can weld and bolt using the factory cover bolts it will add strength, also if you weld what precautions to you plan on taking to avoid warping the cover causing seal issues??  so educate me here what was wrong with the OEM diff, what diff did you install a year ago, what was wrong with it, how hard was it to get the rest of the components to graft to the non BMW differential, and what made you decide to go with the Ford unit???

Daze wrote:

Ialso if you weld what precautions to you plan on taking to avoid warping the cover causing seal issues??

The cover itself is made of 1/4" steel plate while the flange is 1/2" steel.  As such I don't anticipate any warping however, the cover will be bolted to a welding table during welding. If any warping occurs, we will mill the flange flat  again. Again I don't anticipate will need to mill anything.

Daze wrote:

so educate me here what was wrong with the OEM diff, what diff did you install a year ago, what was wrong with it, how hard was it to get the rest of the components to graft to the non BMW differential, and what made you decide to go with the Ford unit???

Allow me to quote you "If it isn't broken, modify it anyway"

Joking aside, originally this car came with an anemic ~150 rwhp 6 cylinder engine which has since been replaced with a V8 putting out about twice as much as the original engine. The stock diff was not only to small for the new power but it was also an open differential. I threw it away and replaced it with one of the strongest diffs BMW offers which also has a limited slip diff.(LSD) It is out of an early 90s M5.

However, the LSD in these diffs leaves a lot to be desired especially on the track. Coming hard out of tight corners, you can feel that inner wheel letting go. I intend to remedy this with the Ford diff which has a slew of LSD carriers available for it at very reasonable prices. I also intend on minimizing the diff flex issue with the new setup. The numerous gear ratios available for the Ford diff is a bonus. hope that helps.

Ralphy wrote:

Another C4 IRS, motion shots of c4 irs in turbo bmw e30.
http://www.youtube.com/watch?v=XvxLdSQxwP0

Nice shot. They did a great job of setting up that rear. Seems very confident even under power.

By the way how do I get rid of the Verification image everytime I have to post?

Thought I would update this thread with the finished product. It turned out great

Thanks Ralph. Yes, it's in with ~150 easy miles as I'm currently breaking in the gears. 
By the way, great link to IRS videos. I clicked on one and next thing I know 2 hours had passed!

Last edited by Schitzo (9/15/2013 8:16 am)