Kristian Grimsland
Associate Editor, Muscle Mustangs & Fast Fords
February 1, 2013

Installing lowering springs to drop your Stang is one of the first mods many owners do. The effect often has great visual appeal, plus it can improve performance and handling.

When done right (read: with the use of good parts selection and setup), the result is improved handling with little degradation in noise vibration harshness (NVH). When sub-par or mismatched parts (springs and dampers) are used, your handling can be downright ill. We've all seen or driven cars that have harsh ride quality, and despite being low, actually don't handle that well.

Having excellent drivability and road manners is a main goal for our 1985 LX with Coyote power. Yes, we want to vastly improve the handling for the street and track, but we want it without a kidney-killing ride. Thankfully, suspension guru Kenny Brown of Kenny Brown Performance has a sweet setup in his AGS 5.0 components. With the new four-bar arms and coilover dampers, we'll soon be carving corners with some of the best supercars.

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Fox Mustang Chassis Defined
The Fox chassis has been a favorite for a long time. The design was introduced in 1978 in the Fairmont and Zephyr. Ford developed a diverse unibody chassis that was used not only for the Mustang, but also the Fairmont, Capri, Thunderbird, and other vehicles. It proved to be simple in design and easy to modify.

Over time, the Fox chassis had major success on the street and on all types of race tracks. Fox Mustangs are a favorite amongst drag racers especially. We'd say Ford, and many enthusiasts, struck gold—however, the platform showed its weakness when pushed to the limits of performance on track.

The lightweight unibody is also rather flexible and is prone to cracking in critical areas, namely the torque boxes and the floor, when big horsepower or torque is applied to the control arms that push and pull on the chassis. Therefore, your car may be susceptible to wear due to a lack of torsional rigidity, so strengthening the unibody is a must. Thankfully fortifying your chassis is easy.

All '79-'04 Mustangs were designed with a similar unibody construction that uses a triangulated four-link rear suspension and a modified MacPherson strut setup in the front. This system is easy to understand and easy to modify for better performance.

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The rear design consists of two upper and two lower control arms (also called trailing arms) to connect the rearend to the chassis and to limit side-to-side movement (of the rear). There are two springs to support the chassis (which rest on the lower control arms), and shocks to control dampening. The rear of the Kenny Brown system is engineered with coilover Koni shocks and his AGS control arms with revised geometry.

Likewise, the stock modified MacPherson front end is lightweight and simple in design, but lacks the benefits for maximum performance. The KB system utilizes a tubular K-member, tubular lower A-arms with revised geometry, Koni coilover struts, and adjustable caster/camber plates to dial in the alignment.

So when you're looking to improve the aspects of handling—such as reducing body roll, dive under braking—combined with more accurate steering and not trash the ride quality, you'll need to assemble a system of parts that is professionally designed and track tested.

Mustangs are also notorious for plowing/understeering and excessive nosedive during hard braking. This can cause rear lockup and make your Pony skiddish under hard braking. By adding anti-lift to the rear suspension, the rise rate of the back of the car under hard braking is greatly reduced. This gives you far better performance, control, and road feel.

Due to its design, the stock four-link suspension tends to have a very high-rear roll center. When under hard cornering and accelerating out of a slow corner, Mustangs have a tendency to lift the inside tire. When creating a lower roll center, the result is a lower point of rear rotation, reduced body roll, and thusly increasing handling performance and control.

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1985 LX Coyote Coupe—Reengineered
If you've been following this build for the past year or so, you've seen what we started out with when we brought home our 1985 coupe. When the LX first rolled into the shop, it was basically a shell with wheels—and the task of rebuilding it was a little daunting, to say the least.

As of today, we've given it an entire new identity with the installation of a Ford Racing Performance Parts Coyote 5.0L, new paint, Scott Rod Fabrications rear-seat delete, and American Powertrain Tremec T-56 Magnum six-speed transmission, and dyed our interior with help from National Parts Depot. Finally, everything is starting to come together.

Kenny Brown was actually in town when we first brought the coupe home, so he saw our Fox first-hand and wanted to be involved in the project. Upon returning to his home base, Kenny sent us his Advance Geometry System (AGS) 5.0 suspension kit, which includes an Extreme Matrix chassis-stiffening brace, subframe connectors, front tubular K-member, caster camber plates, front control arms, rear upper and lower control arms, and front and rear coilovers (a variety of shock/struts are also available).

To lend us a hand, Brad Grissom from Kenny Brown made his way to our Tampa headquarters. With his help, we installed our new suspension. Grissom is an expert in suspension geometry and has had his hands in many Foxes, so we were confident we would get the parts bolted up with little hassle.

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According to Grissom, the first thing any Mustang enthusiast should do to improve the handling on their vehicle is to start with the chassis. “The biggest cost versus value is the money you put into the chassis,” Grissom said. “By strengthening the chassis, in theory you are stealing back horsepower and handling performance that is robbed by the chassis due to a weak design.”

If you look at a bare Fox chassis compared to the newer S-197, you'll find the new car is robust in the important areas, such as the rockers, suspension mounting points, plus the floor, tunnel, and overall frame structure. This adds to rigidity and prevents flexing of the unibody, which is a big problem in the Fox vehicles. That's why any unibody strengthening will enhance the performance of your suspension.

In other words, how can you expect good, consistent handling if the chassis (and thus the suspension pick-up points) is moving under load? And that's why we installed not only the KB Matrix system, but also a KB Street Cage first.

Now, follow along as we get the suspension in place, and in short order we'll have the Chris Alston/Strange rear buttoned up and we'll also have our Wilwood brakes installed. We're itching to get the coupe back on the ground so we can plumb in the fuel and cooling systems and then hit the road.

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