A method of measuring chassis torsional stiffness is shown. All shock absorbers and three wheels are replaced with steel members. Car is lowered onto the one front steel member and the car twists under its own weight. Two laser pointers are mounted to the chassis. One laser is mounted to the rear subframe near the upper shock mount, the other is mounted to the lower radiator support. The lasers point to a fence 80 ft away; turning the slightest movement of the laser into a large movement on the fence. Measure the difference in height of the laser dots to figure angle of twist. Use the RIGHT REAR corner weight for the load (if you use the steel beam on the left front). Divide these two quantities to determine the chassis torsional stiffness in ft-lbs/deg. The stock chassis was found to be about 6,100 ft-lb/deg using this method.
Note that a rollover bar is installed in the photo. Using only the NHRA required tubing members, there was no significant increase in torsional stiffness versus the stock chassis. With the addition of four members, connecting the shoulder nodes to the shock towers and diagonally across the rear seats, the stiffness was increased to 13,500 ft-lb/deg; a substantial difference. These members are visible in another photo. See that photo here:
