[aggie91]

I agree with Kieth also. His #5 above is what we are trying to improve by boxing the frame. A boxed frame is now a rectangle in cross section as opposed to a C shape for an unboxed frame. A rectagle tube has a better section modulus than the C for a give material. For the welding reducing the yeild strength of the material, that is true, but if you reduce the yeild from 55,000 psi to say 40,000 psi, than your RBM for "new" box is now = 680,000 for example 5b above, still an improvement over the stock number of 605,000.

Now for a frame on a '66 that is not heat treated, the improvement would be a larger precentage. In example 5a 6+2.5+2.5x30,000(mild steel yeild strength) = 330,000. The boxed version (5b) would be = 510,000. That is a 54.5454% improvement in RBM.