Independent rear suspensions...
Independent rear suspensions such as the one on this Mustang Cobra are the exception to the rule, as they were only available on the limited-production Cobra models. The unique handling attributes of the IRS is a story in itself, but know that the aftermarket has you covered when upgrading it.
As with most performance parts, all coilover kits are not created equal, and you'll want to compare the features of each.
"We designed our threaded sleeve assem-blies to fit snugly on the struts and shocks," Schwynoch says. "The tight fit keeps the threaded sleeve from rattling on the strut. More impor-tantly, the lower spring perch is kept square to the strut and shock, reducing the chance of the spring bowing and rubbing on the threaded sleeve."
This is just one of the many reasons to do your homework before going out and dropping big coin on a hot suspension setup. No matter how good these setups are, they need to be optimized for each application. The various manufacturers can help you out with choosing the right shocks, struts, coil springs, and spring rates.
Chassis Stiffening
Since the unibody structure is the foundation for your performance vehicle, it must be strengthened to handle the increased loading and stress often encountered in performance driving. The Mustang aftermarket is chock full of components to accomplish just that, and what's better is that the parts are generally inexpensive as well.
Why does the chassis need to be stiff? There are a number of reasons. The chassis in your car was designed to provide a relatively rigid structure given the vehicle's power output, weight, suspension setup, and engineered crash structures. When you increase power and/or suspension stiffness, the added stresses are transferred throughout the chassis, and this increases the load or stress on the structure. Constant flexing could create chassis damage or misalignment of the suspension pick-up points. That's why drag racers tear out torque boxes, C-pillars crack at the roofline, and strut towers are tweaked out of alignment.
By stiffening the chassis, the main structure of the vehicle, you reduce flexing, and this in turn allows all parts to perform better. You get to put the power down sooner and harder, and your suspension will be more predictable.
The most common chassis modification Mustang owners make is subframe connectors. If you take a gander beneath your Stang, you'll notice there are framerails stamped into the chassis at the front and rear of the car. The problem lies in the fact that Ford never connected them (until 2005, that is), and in a rear-wheel-drive application, the chassis flexes right in the middle, which causes all sorts of problems. Subframe connectors tie the two sets of framerails together to make the structure more solid. There are quite a few types, from bolt-in, to weld in, to custom units that require the floor of the car to be sectioned out and the new rails welded into the structure.
Another popular modification is the strut-tower brace. This device was originally called a "Monte Carlo" brace because of its use on Ford Falcons used in European rally racing. This bar ties the two shock towers in the engine compart-ment solidly together, and they are usually triangularly fixed to the chassis firewall. Under hard cornering situations, the shock towers can flex (in and out), which doesn't allow your sus-pension components to do their jobs properly. Ultimately, having a stiff chassis will allow the suspension parts to move in and out or up and down consistently over time.
When applicable, the ultimate chassis stiffening modification is a welded-in rollcage. A properly installed cage, or at minimum, a rollbar, ties into critical chassis points to triangulate them, thus providing not only safety for the driver, but torsional stiffness as well. Beyond the roll-cage, a full-tube chassis can be constructed to replace the factory unibody chassis and support the body components and drivetrain.