Stiffening the Chassis

From 3.8Wiki

So you've gotten your Mustang's suspension setup to drag race, open track, autocross, or just enjoy on the open road, and now you want to stiffen the chassis a bit to help the suspension do its job a bit better? With a few simple modifications or some not so simple modifications, depending on how far you want to go, you can have your Mustang's chassis solid as a rock.

The most common and simple chassis modification, which happens to be one of the most effective as well, is the addition of subframe connectors. The Mustang has no real frame, as it is of a unibody contruction where the body IS the frame. Instead of a true frame, there are two separate subframes under the car, which the front and rear suspension bolts to. The front subframe consists of two rails starting in the fenderwells, and traveling down under the car, parallel to the transmission tunnel, stopping about halfway down the door. The rear subframe starts under the rear seat, travels up into the rear wheel wells, and ends at the rear of the car. Connecting these two subframes together really helps to cut down on overall flex in the car, keeping suspension geometry in line, and allowing the suspension to do what it is designed to do.

You have two basic types of subframe connectors, standard and full length. A standard subframe connector touches each subframe rail with just a few inches, just enough to get the job done. These work very well on daily driven, or occasional track cars. When you start getting more serious, a set of full-length subframe connectors will be of great benefit. The full length connectors start as far forward on the front subframe as possible, and reach as far back on the rear subframe as possible. Since the connectors are almost always of a more substantial metal than the stock subframes, the additional length really helps cut down flex in more serious situations.

Another type of connector that I haven't mentioned are "through the floor" subframe connectors. These are a much more involved process, and are usually only installed on open track type cars. If you are looking to install these, you don't need an explanation. :)

If you are drag racing often, or are using sticky tires, you should think long and hard about seam welding the torque boxes (control arm to chassis attachment point) and/or installing torque box reinforcement kits. From the factory, the torque boxes are spot welded, and with much torture, these spot welds can be ripped apart, causing pops, creaks, moans, and in seriously injured cars, a complete separation from the car. Welding all the seams of the torque boxes up helps prevent this, and as extra insurance, a lot of people choose to install torque box reinforcement kits (also known as "battle boxes") to help brace these critical points.

Even more serious? The next step, or should I say giant leap, would be installing a 6 or 8 point roll bar in the car. These have a main hoop that is within 6" of the drivers head, rear struts coming down from the hoop into the trunk, and two door bars going by the driver's shoulder/elbow area to the front floorboard. An 8 point bar adds two bars going from the sides of the main hoop down through the floor attaching to the subframe connectors.

These types of rollbars add a great deal of stability to the chassis, tons of driver safety, an attachment point for the shoulder harnesses of a 5 or 6-pt harness, and reenforce the back of the driver's seat. If you plan on running ~11.50 or faster in the 1/4 mile, and don't want to have your fun interrupted, plan on installing a 6 or 8 point rollbar.