on a 240sx forum not too long ago, included information from a major car company's test results for different density foams. How much weight was added by the foam? Don't you think seam welding is going to add a bit much weight? I will assume that you are doing some sort of welded roll cage since it is a race car, then my question would be why even bother with seam welding the entire car and foaming? Nice project & keep it up!!