Detroit Speed's How to Build a Pro Touring Car. Tommy Lee Byrd

it served as the first of many unibody vehicles built by the General.

      Two years later, the Chevy II was introduced; it was a much more conventional compact car for the time. It, unlike any other vehicles at the time, had a bolt-on front subframe that was obviously a manufacturing decision designed to save the company time and money. But, hey, it turned out to be a great move for Pro Touring guys because it allows easy subframe removal and installation. A few bolts here and there, and the entire front end of the car can be removed. Brilliant.

      When General Motors joined the “pony car” market in 1967 with the Camaro and Firebird, it introduced its F-Body chassis design, which has turned into the most popular Pro Touring platform in the industry. The F-Body continued the bolt-on front subframe approach, and later passed it on to the 1968–1974 Chevy Nova, and BOP (Buick, Oldsmobile, Pontiac) equivalents.

      As mentioned earlier, Mopar used unibody chassis construction for many years, even on its full-size cars. When the muscle car and pony car craze hit in the mid-to-late 1960s, Mopar had a number of high-performance models, all of which featured a unibody construction with torsion-bar front suspension and leaf-spring rear suspension, a common design element in most of its models in the Chrysler, Dodge, and Plymouth lines.

       Chrysler Corporation relied heavily on the unibody platform, but its chassis designs featured an integrated front and rear frame section. Large cars, such as this Dodge Charger, are a little too heavy for high-performance handling without first installing additional bracing and subframe connectors.

       Ford also used an integrated front and rear subframe. This Ford Mustang has the floorpan removed for rust repair, which shows exactly how much this chassis relies on the structure of the sheet-metal floorpan. This chassis is greatly strengthened by extending these front subframe rails to meet the rear rails.

       Subframe connectors are pretty simple pieces of metal but they’re very important chassis components. If you’re serious about building a Pro Touring car with a unibody chassis, a pair of weld-in subframe connectors is a must-do modification to take advantage of the new suspension.

      The Mopar crowd doesn’t get much love in the Pro Touring world but many of the Mopars from the 1960s and early 1970s are very capable performers. It’s just a matter of strengthening the unibody structure with subframe connectors and adding a mild roll cage to have a great platform to build upon. Aftermarket support for Mopars isn’t quite up to par with the GM brands but if you’re willing to shell out some dough for custom components, you can make a Mopar handle with the best of them.

Subframe Connectors

      Despite the difference between the Big Three’s attempts at unibody construction, they all share the same problem: strength and rigidity in harsh driving conditions. Drag racers and road racers deal with the same struggles when dealing with unibody cars, so the idea is to remove the tendency for the chassis to flex under hard loads. The answer, in most cases, involves fabricating or installing a set of subframe connectors. The connectors are self-explanatory, connecting the front portion of the frame rails to the rear portion of the frame rails. In other words, they provide support in the middle floorpan area, where manufacturers relied solely on the floorpan and rocker panel structure to take the abuse.

      Luckily, subframe connectors are usually an easy install. Some are bolt-in style, suitable for a guy building a car in his driveway, but they tend to hang below the rocker panel pinch weld to avoid the dips and pockets in the stock floorpan. This obviously isn’t the most attractive look, so most hardcore Pro Touring enthusiasts go with a weld-in design that is recessed into the floorpan.