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.
1 Stiffler’s, by Innovative...
1 Stiffler’s, by Innovative Performance Technologies, started by using dial indicators and twist-testing the body of a Fox Mustang. It also later performed the same tests after installing its new components. Similar tests were performed on an SN-95 as well.
2 The transmission crossmember...
2 The transmission crossmember serves as the mid-way point for the Spider Brace. The front braces attach to the front of the crossmember and extend to the lower chassis brace, and the rear braces attach to the rear of the crossmember and extend to mounting points on the subframe connectors near the torque boxes.
3 One of the unique features...
3 One of the unique features of the Stiffler’s brand is the Spider Brace. Seen here, the Spider consists of a lower chassis brace ($85), transmission crossmember ($145), and the adjustable braces ($189).
"What was needed was a way to gain additional support to the rails and a means to transfer those loads to the main subframe system. So we devised a small group of parts that when installed acts as a lower chassis rail in a full tube-frame car. This was accomplished by taking our lower chassis brace, which attaches to the K-member, and connecting it to the subframe system with a series of adjustable bars we call the Spider Brace. With these parts, front-end rigidity is dramatically improved."
Knowing that an experience engineer and Mustang enthusiast developed these innovative products would be enough for some. But what's more than that is the attention to detail that was taken when developing the parts. For instance, weld locations are protected from the powdercoating process by pieces of easy-peel plastic so you don't have to grind on your new parts to install them properly. Also, the web brace comes with slip-to-fit ends. This eliminates hammering the components into place, providing easier installation and a better fit.
We requested a pair of the subframe connectors for our SSP coupe, but Figg sent an entire system. Instead of installing it on our daily driver that only sees track time for component testing, we're going to save it for a more hardcore build in the near future. However, we did install the subframe connectors, since the old coupe needed them.
Follow along as we introduce to you the entire Stiffler's kit for a Fox-body and install the subframe connectors on our SSP.
4 The lower chassis brace...
4 The lower chassis brace bolts to the stock K-member and is used to tie the Spider Brace to the framerails.
5 The transmission crossmember...
5 The transmission crossmember is made of lightweight tubing, and includes strong polyurethane bushings and all the mounting hardware necessary.
6 The Spider Brace bars are...
6 The Spider Brace bars are threaded, and include all the necessary mounting hardware. Like all Stiffler’s components, they are also powdercoated in satin black.
7 The web brace ($215) comes...
7 The web brace ($215) comes with adjustable ends for easy installation. Stiffler’s even left the areas to be welded uncoated to make installation a breeze. Required for web brace installation are the subframe connectors ($159) and stiffening rails ($70).
8 Stiffler’s also covered...
8 Stiffler’s also covered areas on the subframe connectors to be welded with contact paper before powdercoating. All you have to do is peel the plastic pieces and weld the pieces right in. You can paint the exposed area once you’ve completed the installation.
9 Another component Stiffler’s...
9 Another component Stiffler’s offers is the driveshaft loop ($78). It will either bolt to your existing stock transmission crossmember or the Stiffler’s tubular crossmember.
10 After installing the subframe...
10 After installing the subframe connectors, the web brace is tacked in.
11 Finished product on the...
11 Finished product on the outside...
12 This is what the FIT system...
12 This is what the FIT system ($420) looks like completely installed on an SN-95. It consists of the subframe connectors, stiffening rails, and web brace.