Custom Torque Box - Passenger Side

Purpose:
1) Chasis Strengthening

Here is the finished project (12ga metal). A passenger side torque box is one of the most common chassis strengthening projects for a classic mustang. A must-do if you want to beef up the unibody chassis. You can buy a repro 14ga torque box but if you go it this way you can customize the project just how you want it. Whether this is better then if I had purchased a repro box and welded it in, I don't know, but I got to use 12ga metal and it's exactly how I want it.
This is the bottom of the completed box where it meets the toe pan above the floor support. The gap between the torque box and the toe pan came out very even so that is a good sign I did something right.

Here's the starting point. It's a nice large easy area to work with.
As with many of the projects I start out with a template to get an idea of just what it will take to get this done.
I got a pretty decent fit but I want it flush up against the firewall where the curve is.
Here you can see the cuts needed on the left side of the plate to bend it up flush against the firewall. I used a 1/16 wide cut off wheel but you can use a 1/32 to minimize the loss of metal in the cuts. Either way, I will weld these in later.
A shot from the front. The clamping isn't too bad, just make sure to have some wide deep clamps. You can either purchase them or make your own. The plates are flush up against the rocker panels and it will not be spot welded.
Here I have the upper plate welded in place and have already cut my bottom plate and started fitting it.
A nice inside shot of the box with welding done. Continuous welding all along the edges on teh upper plate. Some intermittent welding on the bottom plate, but there is a continous weld on the underside of the bottom plate so it's really overkill now. The 12ga plate will snap before these welds do.
The third plate template. These templates are not perfect but they are close enough so that any gaps can be filled in with welds.
Here is a shot of the final plate which I have already cut as needed.
Before I seal the box with the last plate we need to get the inside of the box prepped. I sealed these welds with seam sealer which works as excellent corrosion protection over bare metal.
Can't forget to primer the inside.
...and the outside.
The final prep was some spray undercoating. This is the inside of the torque box.
This shot shows the spot weld areas prepped for the toe pan.