[alfavirusnz]

rkirkpatrick is right. Alfa Romeo, along with Mercedes Benz, Citroen and Rover were designing crumple zones well before it was fashionable,commonplace, or mandatory. I have literature indicating this fact, as obviously rkirkpatrick has. Alfa was amongst a small group of manufacturers whose engineers seemed on a mission to produce a "better" car simply almost as an intellectual exercise rather than the purely commercially driven (and ultimately more successful) manufacturers. Certainly with frontal or rear impact the zones appear to work quite well although because of the infancy of this aspect of design the zones would not work as effectively as a modern obviously.
I`m for seam welding the passenger cell, especially along the sill to floor area but would leave the front and rear segments alone. I have done this to my Giulia Ti and the increase in torsional stiffness is noticeable.

 

[alfavirusnz]

Jema, I would strongly suggest seam welding the passenger cell area of your car. The benefits outweigh any negatives I can think of.

 

[alfavirusnz]

That photo is how it is done. I also did all joins inside of the cabin too in my Giulia Ti. Essentially the passenger cell/tub is where you want the added strength for both increased torsional strength and increased protection. The front and rear portions shouldn`t be altered too much for a road car as it is these that are your energy absorbing parts and if in good condition are more than adequate for a road car providing you don`t go silly with tyre sizing. These structures are designed for soft well controlled suspension and limited grip (controllable slide) Increase the firmness of the suspension too much or the grip too much and you load the structure beyond what was originally intended.

 

[alfavirusnz]

To verfify the increased torsional rigidity on my Giulia I just jacked the car up on one corner and tried opening and then closing the doors. Prior to my seam welding the doors stuck ever so slightly. After doing the welding the doors open and shut faultlessly plus the car does not rattle on a rough track I use and subjectively feels much better on the road. I did the same test on our Lancia Fulvia 2C which I have yet to seam weld and like the Giulia was the doors are "sticky" (although it doesn`t rattle like the Giulia did). I will be seam welding this. The Giulia doors now close perfectly with just an gentle push from around 6 inches, very old Lancia or Rolls like.