Marc Christ Associate Editor
August 18, 2011

Unibody vehicles such as Mustangs offer many benefits to the manufacturer and consumer, like affordable price, lightweight construction, and increased fuel economy. However, the things that can make the unibody design desirable can also make it weaker. Lack of complete framerails gives the lighter, less-rigid body opportunity to flex. The effects of this flexing can be felt immediately (especially in drag racing and road racing applications) and can also create long-term problems like metal fatigue. This fatigue is what causes Fox-bodies to creak and squeak over the years. Thankfully, Ford has greatly improved the design in its S197 platform. In true Mustang aftermarket fashion, many companies have developed subframe connectors, strut/shock tower braces, and chassis-stiffening kits to remedy Fox flex. Some racers just weld their rollcage through the floor to the subframe connectors, but for most, a bolt-in or bolt-and-weld-in chassis-stiffening kit is plenty.

New to the market with an original product is Stiffler's by Innovative Performance Technologies (IPT). Brian Figg, a former Indycar engineer, formed IPT a few years ago, initially as an engineering consulting firm. Its flagship product offers up a full line of Fox and SN-95 chassis- stiffening components-as well as some Lightning and S197 products. It offers components such as the FIT system, lower chassis brace, web brace, and the proprietary Spider Brace, all of which we'll explain in more detail later.

"I worked for suspension component manufacturer KYB Corporation for five years... (then) I went back to Indycar racing for 10 years. A few years ago, I left the racing world and began working for myself, doing engineering consulting for several automotive-related clients," says Figg. "Having owned several Mustangs, it was at that time I became interested in the Mustang performance market as a business, and began to work on new chassis product ideas."

Being an engineer (and self- proclaimed car-geek), he began collecting data to identify the problem areas and getting a feel for the market and the subject at hand-Mustang chassis.

"We gathered a Fox-body and an SN-95 car and built a fixture to properly hold them for twist testing. Next, the cars were instrumented with a collection of dial indicators, all strategically located along the bottom of the car. A load cell was then paired with a hydraulic cylinder, which allowed us to measure the amount of force being used to twist the car. A series of tests were then run at increasing loads while the dial indicators recorded the amount chassis deflection. This data gave us a 3D view of what the chassis was actually doing when under acceleration, turning, and braking. We then analyzed and used that information in the design of our FIT System products. As each design was completed, a prototype was made and installed on the car, and the twist tests were repeated to confirm the part performed as needed."

The result was the FIT System, which consists of a typical pair of subframe connectors, a web brace, and jacking rails. But the IPT team didn't stop there. It added a transmission crossmember, a lower chassis brace, and the aforementioned Spider Brace, which ties it all together.

"We discovered the huge amount of vertical deflection in the front framerails caused by suspension loading. Several key issues arise from this movement, most notably the front suspension geometry (alignment) changing as the rails hinge up (OEM or aftermarket K-member). For the road racer or street driver, this happens most frequently under braking and cornering, right when you depend on the suspension alignment the most. The drag racer will have this happen as the car launches-the rails will droop down, slowing the weight transfer time to the rear wheels, thus reducing traction and increasing 60-foot times.

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