Torsional frame flex reduction

[exwestracer]

If I could rephrase the op's question....would the x frame be stronger torsionally than a simple bolt in crossmember?

Ray, how would raising the sills (making them taller) help with torsional twist?

Donny, if we look at the frame as a whole, torsional flex is really bending one of the rails up in relation to the other. This load is balanced out at the spring pickup point at the opposite end of the rail.

Now, I DID make an assumption that the front and center crossmembers are holding the rails stable at those points. If we ran tubes from the front spring pockets to the top of the kickups (basically the bottom half of a roll cage) we would be removing the hinge point between the front spring load and the opposing spring load in the rear. Basically, the higher sill is acting like a big "gusset" along the same lines. Not as effective, but there isn't much else you can do without going right through the center of the car. That's actually why the original 300Sl Mercedes had to have a gullwing door. The sills were raised radically to help torsional stiffness.

And, yes the X member would be better than a bolt in straight crossmember. How much better depends on how tall the material is and how much notch has to be taken out of the center for trans clearance and a mount.