These days, GM has the unibody thing all ironed out. The result is lightweight chassis that are substantially stiffer and stronger than yesteryear’s full-frame cars, and for resounding evidence, look no further than the fifth-gen Camaro. Not only does it handle the tremendous loads imparted by 426 hp, 4,100 pounds of mass, and over 0.90 g of lateral grip, it does the deed without main ’rails running along its perimeter to help stiffen things up. Unfortunately, even full-frame cars of the ’50s and ’60s aren’t nearly as stiff as modern unibody cars, and twist up like the storyline of Lost once some modern horsepower and tire grip are thrown into the mix. Recognizing this problem long ago, companies have been churning out chassis stiffening components for quite some time. Unlike unibody cars like Camaros and Novas that can be substantially stiffened up with subframe connectors and aftermarket front and rear clips, there is no easy fix with full-frame Tri-Five Chevys. The solution is engineering a completely new frame from the ground up, and innovative aftermarket chassis builders have done just that. To find out what’s involved in pulling off such a conversion, and how much a full-frame swap can improve ride and handling, we sought out the expertise of the top chassis builders in the business. Thanks to Craig Morrison and Matt Jones of Art Morrison Enterprises, and Steve McClenon of Hotrods to Hell, we got thoroughly schooled on the inner workings of an aftermarket full-frame chassis. Here’s the scoop.
Matt Jones: The original frames used in the ’50s and ’60s were merely a way for the engineers to mount suspension components to some sort of structure as cheaply as possible. Most of the structural integrity was handled by the body, which was deemed enough for the vehicle’s intended usage without much additional support from the frame. By today’s standards, vintage cars with full frames or unibody construction are very flexible. Open-channel cross-sections were very popular during the ’50s and well into the ’80s because they were cheap to produce and provided increased cabin space. Materials were designed to be thin, which reduced material cost and tooling wear during production. Today, much more focus is placed on overall structural strength as a way to improve the overall quality of a vehicle. Modern cars can have more than double the torsional stiffness than vehicles made in the ’50s and ’60s. Chassis stiffness is very important to ride and handling, and factory muscle car bodies need all the help they can get. With increases in spring and roll rates, more stress is placed on the body and frame. Stiffer structures will allow the suspension to work more efficiently, which makes transitional handling more crisp, and also reduces interior rattles by a significant amount. They’re also safer and provide improved ride quality.
While it is difficult to increase the body’s strength, we can focus our attention on the chassis to make sure it is as stiff as possible while maintaining packaging constraints. Designing an entirely new frame allows much more freedom of design than simply designing around an existing frame. Suspension design can be revised for more aggressive handling and to accept modern lightweight components, such as tubular control arms and lighter steering racks. Framerails can be narrowed or shaped to allow wider tires while still maintaining an acceptable turning radius. Finally, material shape and thickness can be optimized for increased strength without gaining too much weight.