How structural is the bulkhead between front trunk and gas tank? I realize the double walled top of the bulkhead that spans the strut towers is probably structural. Specifically, I am asking about the sheet metal underneath that?

I ask because on my project car this was cut out to make space for a fuel cell. I plan to use the factory tank and I have a graft from a donor car to replace it. But, I am considering using the graft to make an access panel (to beneath the tank) and bolt it to the bulk head as opposed to welding it in as a patch.

The upper piece, or a cage equivalent is required. Now the lower wall...

I had to cut a slot out of it for my fuel cell, just not the whole thing, and I have the fuel pump and filter fastened to it. In your case, I like cross bracing in that area in lieu of that entire piece. But it appears your cell may be in the way of that mod.

I wouldn't replace it. However, if you're going to race the car and or seriously stiffen the suspension, I'd make some attempt to cross-brace the strut mounts if possible. If it's a street car then it's not as important especially if the suspension stays "on the soft side".

Good luck

Take a coat hanger and pull it into a rectangle. Then tape it to the workbench with the shape standing up like a picture frame. then push the top corners of the frame right and left. Now cut a piece of cardboard the shape of the wire frame rectangle and tape it all around the wire frame. Now try to push it left and right. The upper towers were designed to hold the camber force of the struts with this bulkhead as part of the design. You could add an X of V brace to the open space and that will handle the stress load.

It's a shear load as Rick said.
You either need an x brace to take that load, or the piece of sheet metal.

Rich

Most racecars have the area below the top cut out for the fuel cell. I added some bars to the top after cutting the sheet metal out for my cell.

Hmm... Thought provoking responses....

I found a picture of it from when I bought the car.... What you can't see is the hole goes all the way to the hump for the lower X member.

In addition to the shear force from the struts, that sheet metal also works in conjunction with the spare tire to absorb/dissipate force from a frontal impact. Of course, if there is a fuel cell in place of the spare tire, this is a moot point. Just try not to run into anything.

I don't think you need to do anything. The structural coss-member is still there. But then again I have a Lotus and it doesn't have any support anywhere.

That's not too bad. I pictured the panel cut out from wheelhouse to wheelhouse.

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Here are better pictures. One of the hole, another of the graft. I could make a patch panel out of the graft. But I am trying to cut a corner on fab work and gain a bonus with access to under the tank for those rare times you need it. But, I don't want to do it at the expense of structure or safety. This is not a restoration, but more of a racer wannabe build.

BTW car was an AC car and will get a front mounted oil cooler.

Click to view attachment

Click to view attachment