Cage work finnaly begun!

Spent all day on Saturday working on my friends Dimitri's E36 race car assembling his new rear suspension setup. It was SOOO FREAKIN hot!!! Must of been like 110 at least! We got thru the day drinking lots of water and sweating about twice that and finished his car.

Started sunday by watching F1 with My mom and my stepdad. GO MASSA!! Go Senna!

Then it was back to working the the OVEN they call the valley. Today we towed my car to the shop with Dimitri's X5. Which we like to call the ultimate tow vehicle! I wish it was mine.... the pair looks so good, don't they?

I decided to start work on the cage from back to front. That is to say I will start in the trunk and slowly work my way to the engine bay.

First order of business was to remove the awkward bar spanning across the 2 down tubes. I cut it out with the mighty sawzall then ground down the nub and painted it.

After grinding.....
after all painted up!
Next I used the same tube I just cut out to serve as my strut tube. You might ask me why no baseplate? Well I considered it, but as you might be able to see in the pictures the metal on that strut tower is VERY thick around 1/8". So I decided the best thing would be just to weld the tube directly on the strut tower. I will not be using coilovers so there really is not much load in this area. As my "downbar X" will be welded to my strut tube In case of a roll over the load will be shared by both mounting points. I did not design or install the original cage (ireland Eng. did) or else this whole area would of been very different. I'm just "modifing and adding" to the existing cage so keep that in mind.

Now after I welding in the "strut tower tube" I added the "diff tubes".

Quick flex test of this area I did today- I jacked the car up from the diff mount and I could actually see the floor board moving up or "bowing" from the center maybe 1-2mm at least. I was surprised by the amount of flex I observed! Now all the suspension forces that come thru the rear wheels make there way into the chassis thru the suspension arm into the subframe and into the car thru the subframe mounts. The other load path is thru the spring pads. The third and last location is the diff mount and the suspension loads and diff power "torquing" that might occur all transfer into this area.

TO address this I have seen this done many different ways. The diff mounts in 2 points on what basically is a square tube that spans in-between the strut towers along the floor. So the best solution would be to cut the tubing open (ala e36 subframe tie-ins) weld a plate then a tube sticking out. Then plate cloe the hole and weld you connecting tubes to it..... that's a bit too involved that I'm willing to go right now.

Another way I have seen is to tubes meeting in the middle of the trunk.....this seemed silly as the diff mounts in 2 spots and not is the center.

this pic from another 2002 race car build shows the diff mount and the tubing well.
I decided to go with 2 tubes mounting to the area directly above the mounts. Pretty much like the pic above. Now I understand I'm not actually connecting the tubes directly to the diff mounts but the large plate and the 2 tubes will greatly increase the stiffness of the area and now any loads will be transfered up into the cage instead of bending the floor.....

There are 10,000 to cook potatoes...this is just how I cooked mine.
Also this leaves a nice space in the middle to mount the battery!
here you can see the diff mounting bolts in relation to the tubes. I used 1.5"x.120 wall DOM for the strut tube and 1 1/4"x.120 wall DOM for the diff tubes.
....and that's as far as we got in today slighty cooler 100+ degree heatwave......

Why do I wait till the summer to start working on things like these?