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Message: <blockquote data-quote="wash" data-source="post: 1137797" data-attributes="member: 18190">Evidently Ford started using foam in 98 or 99 mustangs and I've heard several Japanese auto makers use foam.Chassis deflection is measured by rigidly attaching the car to the ground at one end (usually the rear), supporting the other end beneath the center line on the long axis so the chassis could pivot if the other end was not constrained, then hang a known weight off of a lever of known length mounter 90Â° to the long axis and measure deflection with one dial indicator beneath each frame rail (on the free end).With a little trigonometry you can even get a ft-lbs per degree number.I realize that holes are bad but the placement is what matters.  In a lightly loaded panel, holes can be fine because the yield point is never approached. In a highly loaded panel the stress concentration of a hole can cause catastrophic failure.  If you take time to think about it and you know what to look for, its fairly easy to identify areas of high stress.  If you have to drill in a bad place you can plate the area to locally increase the strength or drill oversized and weld in a thick wall tube to restore the strength.People have been doing stuff like this for a long time, even before the manufacturers figured out that full frame rails aren't an efficient use of steel and started making unit body automobiles.  There are lots of techniques used to design steel structures, the trick is knowing how and where to apply them.  I've seen lots of high performance structures, fabricated several, talked design with engineers, taken a few courses and read quite a bit on the topic (hard bound books with more equations and text than illustrations and photos).Considering your theory that chassis rigidity is only one detail contributing to the suspension performance, I'm sure you're right but if I take care of all the details, the big picture will take care of itself. I intend to take care of ALL of the details.</blockquote>