Stiffer body - how to do it?

[16v of E30]

for a good start, you could do the strut tower braces.  they are kinda expensive, but if you have the resources, you can pretty much make them yourself (with a welder)

Another option would be the b-pillar cross bar (hence taking out access to the back seat...)

front and rear sway bars and you should be tight like my other favourite thing...

[HMS_Tim]

The biggest problem with stitch welding the chassis is that it will take alot of work.  You need to go all out and have all the right tools to do it properly.  I do not know what your situation is as far as having a shop or garage.  So I will just shoot some things out.
The only right way to stitch weld the chassis is to do every seam on the car.  It is a unibody design and it should have that unibody riggedness. Meaning each part relys on the others attached to it for strength. The car should be disassembled to do this, and dipped to remove all adhesives and coatings. This however is a tremendous about of work and money.
I would suggest welding the problem / weak areas of the car first.  Such as everything around the rear subframe mounts and all around the trunk area. Shock mounts too.  Up front there isn't a whole lot to do unless you get creative.  Stitch the seams around the strut mounts.  Plating around the strut mounts would add some strength too.  I agree that strut braces are a good solution front and rear.  Easy and bolt on.  Be careful as some aluminum bars are not a stiff as you would think.  Steel is heavier, but it is cheaper and stiffer.
Overall strength is only as good as it's weakest point.  Get reinforcement kits for everything on the e30.  Turner Motorsports makes a nice complete kit.  If you are handy with metal you can fab things on your own.  Just remember the strong welds are clean welds.  You need to get all the adhesive out of the area you are going to weld.  Dirty welds = useless welds.
All of these little things combined will add alot of stiffness to your car.

All of these braces and reinforcement should be done anyway if your going to track the car.  Truct me things break and cracks spread fast!  You would want them done before you do a cage because stiff cage equals weak car. (Hint: weakest point!)

Good luck and we love pictures here.

[Jimmy Lewis]

so do you have some input on where he should look or are you gonna sit there and act like a douche?

Yeah dude, the smiley at the end of it implies he is kidding around, jeeez.

[HMS_Tim]

Check out this site.
It might be some help.
http://www.aceengineering.ca/stitch_welding.asp

[Boyracer]

During weekend I read book about different 3-series. Not sure how reliable their data is but this is what they said about torsional stiffness:

E36 30% better than E30
E46 45% better then E36

So is E30 is 100% as baseline then:

E36 is 130%
E46 is 182%

There are small variations between sedan and coupe models.

[Massimo]

Well if i had the money it would be one of the first things i would do. I find that if i go over a speed hump or drive way on an angle i can here the parcel shelf and door interior panels move as the body twists slightly.

I also know a guy that has a commodor (Australian Car) put some stiff as springs on an in 6 months the car had warped one wheel didn't even touch the ground!!! But then again it is a commodor.

[Royalratch]

Without doing a full race-prep roll cage and butressing, people usually put a strut brace in the front and weld a strut brace between the rear shock turrets under the parcel shelf (inside the boot).

Thicker roofskins with no sunroof also help but that's also major surgery.

[Boyracer]

Here's something about seam welding:

http://forums.bimmerforums.com/forum/showthread.php?t=1093968

[nuvolarossa]

about BMWs structural torsional stiffness:
BMW E36 Touring 10,900 Nm/deg
BMW E46 Sedan (w/o folding seats) 18,000 Nm/deg
BMW E46 Sedan (w/folding seats) 13,000 Nm/deg
BMW E46 Wagon (w/folding seats) 14,000 Nm/deg
BMW E46 Coupe (w/folding seats) 12,500 Nm/deg
BMW E46 Convertible 10,500 Nm/deg
BMW Mini : 24,500 nm/deg
BMW E90 : 22,500 nm/deg
BMW Z3 cabrio 5,600 Nm/deg
BMW M roadster: estimate 6300 Nm/deg
BMW Z3 M coupe 16,400 Nm/deg
BMW Z4 cabrio: 14,500 Nm/deg
BMW Z4 M Coupe : 32,000 Nm/deg (BMW AG's press)
 
dynamic stiffness:
BMW Z3 M Coupe: 29.2 Hz,
BMW Z4 Roadster: 21 Hz
BMW E36 M3 coupe: 29.2 Hz

[miniman917]

the best way to reduce suspension and body movement is to replace all rubber bushings or mounts in the suspension system with heims joints which will remove any bushing deflection. the most important place to do this is at the rear of the front lower control arms. this will make the feel of the ride a lil bit rough but the increased handling should be totally worth it.
a mod like this would be the first step before going to reinforce the rest of the vehicles structure

[JP 91iS]

the best way to reduce suspension and body movement is to replace all rubber bushings or mounts in the suspension system with heims joints which will remove any bushing deflection. the most important place to do this is at the rear of the front lower control arms. this will make the feel of the ride a lil bit rough but the increased handling should be totally worth it.
a mod like this would be the first step before going to reinforce the rest of the vehicles structure

I've never heard of a heims joint, what are they?

[papercutout]

Here you are, heim joints! http://en.wikipedia.org/wiki/Heim_joint

Search google for 'heim joint E30' maybe? I've not tried. Poly bushing will help the car feel 'tight'.

Seam welded along all SEAMS. Search google for seam welding photo's to know the style (seems to be inch of weld, 1/2 - inch non weld, then weld again).

Then rollcage, and boy will your car be stiff!

[swiss318is]

did someone stitch-weld his e30??