Frame/Unibody
Most automobiles utilize one of two types offrames--ladder or unitized body. The late-model Mustang incorporates aunibody design, which is lighter than a full-frame car and morecost-effective to build. The unibody consists of the floorpan, the bodypanels, the front radiator support, and the front and rear subframes,all of which are welded together during original vehicle construction.
Frame Connectors
Because the Mustang uses a unibody frame, it isnecessary to install aftermarket frame connectors to link the frontsubframe with the rear subframe, thus strengthening the entirestructure. Installing frame connectors increases the stiffness of thefloorboard and chassis and greatly reduces flexing of the structure,resulting in better performance from the suspension and increasedlongevity from the chassis. Frame connectors come in many shapes andforms and they can be either bolted in or welded. For the ultimate instrength, chassis builders will section the floorboard of the vehicleand drop in custom connectors, which are then welded directly to thefloor of the vehicle.
Heim Joints
These double-adjustable upper controlarms use Heim joints at the front mounting point. A Heim joint is acaptured bearing that provides movement for the suspension link withoutany bind or deflection.
K-member
The K-member in a late-model Mustang is used to support theengine, along with the lower control arms. It gets its name from theK-shaped design. The stock unit is a steel member that attaches to thefront subframe of the body and provides attachment points for the lowerA-arms and the engine mounts. Aftermarket K-members are usually builtfrom tubular or boxed steel and therefore can be built lighter than thestock stamped-steel K-member.
Pitch Rotation
Simply stated, pitch rotation is the technical term forweight transfer. It is beneficial to have sufficient pitch rotation tohelp hook, but excessive weight transfer can cause giantwheelstands--which don't necessarily make you go fast, but they do getyou on magazine covers.
Roll Rotation
This is noticed as a twisting movement seen on some dragcars during launch. A car that roll rotates badly will lift the leftfront tire on launch much further than the right front. You will alsonotice on Mustangs that roll rotate badly there is a lot of chassisseparation between the left rear tire and the wheelwell, and littleseparation on the opposite side. Excessive roll rotation is wastedenergy that could otherwise be used to drive the car forward. This alsocan upset the geometry of the suspension and lead to poor handlingcharacteristics. Excessive roll rotation can be caused by a number ofthings, including a lack of frame connectors, lack of a rear antirollbar, or mismatched springs. It can even occur from an abundance oftorque or gearing. It can also be caused by worn bushings, a bentchassis, or broken/tweaked torque boxes. Generally, you can solve thisproblem by installing a rear antiroll bar, a stiffer right rear spring(or an airbag), and a rollbar or rollcage to stiffen the chassis.
Rollbar/Rollcage
Most drag cars are equipped with a rollbar or rollcage.The rollbar/cage is a steel structure made from mild steel or lighterchrome-moly tubing built into the car's interior to provide rolloverprotection and to increase the stiffness and/or rigidity of thechassis/frame. A rollbar generally incorporates a main hoop that sitsdirectly behind the driver and is supported with forward and rearwardbars. A rollcage is similar to a rollbar, but it incorporates additionalbars that are placed above and forward of the driver. In addition todriver protection, the rollcage adds strength to the chassis--and insome cases is used as the chassis--to which all the suspension membersare attached. This type of vehicle is termed as a "tube chassis" car.Modern doorslammers (shown) incorporate a Funny Car-style cage to addextra protection for the driver.
Shocks/Struts
Shocks or struts are damping devices that are mounted ateach corner of the vehicle and control the rate at which the wheelsoscillate. For the purpose of drag racing, it is beneficial to havefront struts that are loose on extension because this allows for a rapidrise rate of the front end, which assists weight transfer.
Springs
Springs act to provide a cushion between the wheels and tires,and the body of the vehicle. Drag racers will vary the size, shape, andrate of the springs to alter the effect of weight transfer duringlaunch. A tall, thin-wire front spring can be compressed quite a bit andwill possess a great amount of stored energy, whereas a short, thickspring will be much harder to compress. A short spring is thereforebetter suited for handling because it can resist compression. Commonspring types are coil springs and leaf springs.
Torque Boxes
Torque boxes are specially designed components on a stockMustang that are welded to the unibody. They provide an attachment pointfor the rear trailing arms (also called control arms). In factory trim,the torque boxes (upper and lower) are tack welded to the body of thecar, and under abuse they tend to tear away from the body. For racing orheavy street use, it is necessary to reinforce the torque boxes. Thiscan be done by welding the seams of the boxes directly to the unibody,or by installing an aftermarket reinforcing kit such as the Battle Boxessold by Wild Rides Race Cars.
Photography by the author and courtesy of the manufacturers