Muscle Mustangs & Fast FordsHow To Chassis Suspension
Improve Ford Drag Racing Suspension - Gotta Get Hook
You've Got The Power-Now Use It.
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In almost an instant your Mustang goes from a standstill to an accelerating bullet-the rear tires dig in, the front end comes up, and away you go from the dragstrip's starting line. It's a common theme that thousands of Mustang owners experience virtually every weekend at dragstrips across the country. Drag racing is about acceleration, and the way our Mustangs accelerate is by transferring the power from under the hood through the drivetrain and to the tires.
When we talk about tires in this story, we are referring to drag-racing slicks or sticky DOT tires specifically designed for track use. Regular radial tires are not ideal for drag racing because they lack the soft, sticky compound and proper sidewall construction needed for off-the-line traction. This month, we will explain how the Mustang's suspension plants the tires in drag racing and how you can improve your suspension.
You've spent the big bucks under the hood, and now it's time to utilize all that valuable horsepower and torque. In drag racing, traction requires weight transfer-hence the hiking of the front end in the air during extreme launches. As the tire digs in and the car accelerates, the front end rises as the weight transfers rearward. This helps the tires retain traction on the surface due to the vehicle's mass resting on the rear tires.
Mustang enthusiasts have many different suspension options that range from bolt-on items to entire subsections that can be welded into place that are specifically designed for drag racing. No matter the simplicity or complexity, the aftermarket has what you need to keep the tires sticking to the racing surface.
Upon launching a car at the dragstrip, the driveshaft spins the rearend internals, and the tires turn to drive the car. Meanwhile, the rearend housing rotates in the opposite direction of the tires. Connecting the rear housing to the vehicle are four arms (or three, in the case of S197 cars). It is through those arms that the torque is transferred to the chassis. The front end rises, and the front springs help thrust the nose upwards to transfer weight. The body starts to separate from the rear suspension, and the shocks and rear antiroll bar (if equipped) attempt to keep it straight and proper. That is the essence of what the suspension system is doing when the driver cracks the throttle and sets his or her Mustang in motion.
"These days, the factory bolt-on stuff works great-look at how many people have gone in the sevens with it," says Dennis MacPherson of DMC Racing, owner and lead fabricator at a popular chassis shop that specializes in real 10.5-inch tire performance.
Late-model Mustangs are broken down into two different types of factory rear suspensions (excluding the '99, '01, and '03-'04 Cobras which featured IRS suspension). The '79-'04 cars feature a four-link setup that consists of two upper control arms and two lower control arms. The '05-'07 Mustangs utilize a three-link suspension that has one upper control arm, two lower control arms, and a Panhard bar to prevent lateral movement of the rearend.
Swapping out the factory pieces is the only way to get the suspension to work optimally. The parts that need to get tossed are the stock upper and lower control arms. The factory Ford control arms are stamped-steel pieces and were engineered for regular street driving and longevity, not drag racing. Aftermarket companies offer a wide variety of arms made from a variety of materials and shapes, including aluminum, chrome-moly, and mild steel. The major point is that the arms are strong and can withstand the rigors of hard-launching, full-weight Mustangs.
Adjustable control arms permit pinion-angle adjustment for optimum pinion alignment. The pinion angle is the pitch of the pinion compared to the driveshaft. Optimum pinion angle varies for each application. The pinion angle is always set with the car at rest and the suspension loaded, not dangling.
"If you extend the lower control arms [Extend the length.-Ed.] and shorten the uppers, you will achieve negative pinion angle," MacPherson says. Depending on the combination, he uses anywhere from -5 to -7 degrees of pinion angle. Dario Orlando of Steeda Autosports also agrees that the pinion angle is a crucial part of the equation but uses a different approach. "With the adjustable upper control arms, we like to see around 2.5 degrees nose-down angle in a drag-racing application," he says. Although both chassis experts have different opinions on the pinion angle, given the success of their customers, it's difficult to say whether one is better then the other. In the end, it comes down to the overall combination and what works best on the track. Ultimately, you want the driveshaft and pinion straight when going down the track.
There are other benefits to the adjustable con-trol arms. "By using the Steeda Weight Jacker rear control arms, you could adjust the corner weights of your Mustang when you scale it," Orlando says. The factory four-link setup has the rear springs mounted on top of the lower control arm. Using the Weight Jacker's adjustable spring perch, the car can be balanced based on spring tension.
"Using adjustable upper control arms also allows the user to center the rearend housing," MacPherson says. He offered more advice, like the use of an antiroll bar. Mustangs naturally load the passenger rear tire as the car's torque twists up the rearend and body. An antiroll bar runs across the framerails above the rearend and has two arms that are welded to the rearend housing. This prevents the body from rolling excessively on the launch. Orlando concurs and says his first choice in drag racing would be to run Steeda's Hardcore antiroll bar, but if that wasn't employed, then the car owner should consider running an airbag in the passenger-side rear spring. An airbag is a popular replacement technique to counter body twist. It is filled with air and limits the spring's compression, holding the body in place.
Most of the talk up until now has focused on the factory four-link suspension under the '79-'04 Mustangs. The S197 Mustangs ('05-up) are equipped with a three-link rear suspension that consists of two lower control arms, one upper control arm (mounted in the center), and a Panhard bar to keep the rearend centered (due to the single upper mounting point). This combina-tion is still in its infancy in terms of development when compared to the previous generation of ponycars, but many companies have forged forward with parts development, and the S197 cars are quickly becoming dragstrip stars as well.
The same techniques that work in the factory four-link Fox body chassis applies to the three-link suspensions under the '05-up Stangs. "It works similar because it has similar principles," says Lee Spiker of BMR Fabrication, when comparing the two types of suspensions.
Spiker says replacing the rear control arms makes the suspension rigid, and the user will have the benefit of better bushings. BMR equipment comes with polyurethane bushings or spherical bearings, which remove flex. Spiker suggests the spherical bearing was more for road-racing applications, as that type of racing tears up the polyurethane bushings quickly because of the lateral forces applied in cornering. Drag racers sometimes turn to the spherical bearing in hard-core racing applications, but 90 percent of the S197 Stangs will be fine running a set of polyurethane bushings. Both types of bushings are available from BMR in either the non-adjustable or adjustable upper control arm.
Just like in the Fox-body application, an adjustable upper control arm allows the user to modify the pinion angle. "We like to see -2 degrees pinion angle," Spiker says. He also says the idea of the negative angle is that the driveshaft and pinion angle are straight with each other when the car is under load. This is easier on parts (U-joints, driveshaft, and pinion gears) and will not soak up horsepower due to binding.