OT: torsional rigidity in a u-shaped channel Options

[3liter914-6]

Hello 914ers,

I've got a question that has to do with a Volvo project I'm working on. V8 conversion, and because I'm doing an efan and the engine is a little farther forward in the chassis than standard (due to the t56 tranny), I'm having some issues.

The main issue is that I had to install the radiator 1" farther forward than standard. Not a huge problem, everything still fits, but the radiator is too tall and the cap extends above the slope of the fenders. When I get the hood back on, I'm going to have some problems. What I need to do is lower the top of the radiator crossmember.

It's a U shaped channel, probably about 3" deep. 18 gauge steel, and with a stamped piece of 18 guage steel spot welded to the top of the channel to close it off. I figure to put the radiator in a position where the hood will close comfortably I need to chop about 1.5" out of the legs of the U.

I bounced this off of a friend of mine who is an aero eng. grad student, and he confirmed what I thought--that the strenght of the crossmember is directly related to the height of the U. He couldn't answer my followup questions about whether seam welding and going with a thicker gauge of metal (16 or thicker vs 18) would make up for the lack of height.

He did suggest that filling the enclosed crossmember with a heat expanding foam would add to the torsional rigidity, but didn't have any specific suggestions on products. IIRC a couple of manufacturers do this on their frame rails. Is anyone familiar with this technique, and where I can obtain such a product? Would one of those home insulation spray expanding foam product work (sprayed after all the welding is done obviously)?

I have another question, which is related to cutting the 1.5" out. I'm not good at all with eyeballing a cut, and I can't get a ruler/t-square anything like that on there, as the crossember bows out in places, and I can't just measure up from the bottom as it's not a uniform depth.

I've levelled the car off side to side, and will level it front to rear, so I was thinking I could lay some saran wrap in the channel, and fill it with something like plaster of paris. Something that'll pour in, and setup hard yet still be removable. Assuming I have everything levelled off, I should get a pretty straight and uniform line that I can use as a guide for my cutting. Sound reasonable? Any suggestions on a good material to use? Any other suggestions on getting an accurate cut?

Thanks for any input/advice.

Adam