Rear Strut Tower Brace and Coilovers?

[v8z4]

I'm contemplating making a strut tower brace for the rear shock towers. The attached pic of the BMR F-body brace is just for reference (not the actual part I would use.... would make something similar though). I ditched the "expandable trunk panel" when I decided to install my amp and relocate my battery (prep work for dual exit exhaust) so there is nothing there preventing me from making two plate out of steel, bolting them to the shock towers (using the shock mount bolts), and then tying the plates with a round bar (all welded fixed/no joints). In actuallity it simplifys my life since I currently have to find something to fill the carpet hole where the "expandable trunk panel mounts" were.

Anyone ever seen/done something like this on a Z4? Did it do any good (would think it should do something)?


Now the big "issue":

In the long term I'd like to convert to TRUE coilovers on the rear (along with coilover struts in the front). I have some nice Bilstein ASN aluminum threaded body shocks lying around that I can re-valve and would fit the bill nicely.

I have read where some people have stated the rear shock towers are too weak to support the weight of the car, but the metal thickness measures out to about 2mm (~0.078" or 14 gauge) measuring the rolled lip around the shock. Foxbody (1980s-to-1993) mustangs used 16 gauge (0.0598") steel for their front strut towers (which support V8s and get raced).

Has anyone actually TRIED coildovers on the rear shock tower and had good/bad results? I noticed the shock tower "cap" (top round part) is rosette welded in a number of placed and is should be easy to add weld to the bottom of the "cap" to fully tie it into the tower.

If just welding the lip isn't enough to support the weight, what would be required?

See pictures for visuals:

 

[srhutch]

Can't help you here, but think you mean 2.0mm not 20mm :wink:

 

[v8z4]

Can't help you here, but think you mean 2.0mm not 20mm :wink:

HAHA... thanks for pointing that out. I must have converted 0.78" rather than 0.078"

 

[a340driver]

I'm sure there will be some increase in torsional stiffness. But only minor, the structure is already well braced in that area due to the rear of the boot and the fact that the bodywork extends over the top of the boot. For the money, I'm sure there are more constructive places to invest in benefits.
But I'd still love to see you do it!

 

[bcworkz]

I agree the stiffness benefit is marginal. My gut feeling is the strut tower is only marginally strong enough. It would probably work, but may not really be sturdy enough in the long run. Consider the lip you measured may be much thicker that the rest of the cap because of the way the piece is stamped. Also consider that those round spots may be spot welds, not rosette welds. This indicates a different strength and material thickness than rosettes would.

If you do proceed, do let us know how get on!