I have always though of our chassis as being similar to a shoe boxes, which are easy to twist, especially convertibles which are more like having the top of the box removed.
There was a good video years ago that showed the chassis flex before and after adding bracing. I can't find it now, and don't remember what the company's name was. It had an "X" in the name...
US Cartool and others offer chassis stiffening kits most all of which add the radiator support bracket.
I added their full kit and made my own Monte Carlo Bar which eliminated the last vestige of cowl shake that originally plague my convertible. This completely transformed how my car performs and handles, and is worth looking into. You obviously have the fabricating skills, and your cars are impressive!
"Mopar Chassis Stiffening Solutions
Classic Mopars (A-, B-, and E-bodies) were unibody designs, which, while lightweight, exhibit significant flex compared to modern performance standards. Stiffening allows the suspension to work more efficiently and predictably. Common components, often available as kits from Mopar-affiliated suppliers like Mancini Racing and US Car Tool, include:
- Subframe Connectors: These weld-in components connect the front and rear frame rails, effectively turning the unibody into a full-frame vehicle and significantly increasing torsional rigidity.
- Torque Boxes: These reinforce active suspension mounting points to distribute brute forces, especially during hard launches or cornering. Many B-bodies did not have these from the factory but can be retrofitted.
- Inner Fender Braces & Core Support Stiffeners: These add strength to the front frame rail system, which is prone to twisting.
- Rear Spring Relocation Kits: Often part of a "Level 3" comprehensive kit, these move leaf springs inboard to allow for maximum tire width and improve handling.
- Lower Radiator Support Braces: These provide additional triangulation and strength to the front of the chassis."
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