Muscle Mustangs & Fast FordsHow To Chassis Suspension
Improve Ford Drag Racing Suspension - Gotta Get Hook
You've Got The Power-Now Use It.
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.
The single upper control was first thought to be a burden to drag racing due to the single link and the questionable mounting point. Over time that has been proven wrong, as the single-body mount on the unibody is fortified from the factory. BMR takes it one step further and offers a sturdier upper control arm mount with a lower mounting hole. The lower mounting hole provides a more aggressive instant center, and the car will hit the tire harder.
Unique to the S197 is a Panhard bar setup. It runs diagonally across the rearend housing to prevent the side-to-side movement due to the single upper control arm. An added benefit of the Panhard bar is that it can help tweak the placement of the rearend and set proper wheel placement on either side. The lower control arms act identical as the Fox-body chassis setup.
"We think we have the quickest stock suspension S197 car, and it has run 8.02 at 180 mph," Spiker says. The car he is referring to is the in-house BMR racer that runs a push-rod engine with a single turbocharger and rolls on a pair of drag radial tires. They have received a best 60-foot time of 1.31 from the 3,450-pound ride. Add that to the fact that there are Fox-body Mustangs dipping into the 7.40 range on stock suspension, and it is hard to argue that the factory-style suspension systems can be successful in severe drag-racing applications.
Shocks, Struts, and Springs
Shocks and struts are as important to drag-racing performance as anything else in the suspension system. The average street car will benefit from going to the regular drag struts that have been labeled 90/10 style struts and 50/50 rear shocks. What those numbers refer to are that the 90/10 strut is easier to extend than it is to compress. It goes back to the idea of weight transfer and getting the front end to rise quickly and plant the rear tires. That shock and strut combination has become the standard in our industry for street/strip cars for more than a decade, and it works.
As you can imagine, shock and strut technology has come a long way, and an adjustable set of dampers can be had for only a little more money. JC Cascio of Strange Engineering shared some great information on the advantages of running a set of its adjustable struts and shocks. "The single adjustable strut controls the extension (or rebound)," he says. "The struts control how quickly the front end goes up. When the strut is loose, the front end will come up harder for weight transfer. The tighter the setting, the less weight transfer, which is required in some cases."
When a Mustang leaves the starting line, the body wants to separate from the tire and plant the tire. The shock will help plant the tire harder when run loose, much like the front struts. A stiffer shock slows down the rate of compression, and in some cases that is needed-like when the track is stickier than normal or if the car hits the tires too hard, causing the tires to rebound and break loose. If the shocks are too loose, the rear tires will shake as they grab and spin, grab and spin. If they're too tight, the rear tires will simply spin due to no bite. The adjustable shock allows fine-tuning for that specific car.
"I usually suggest guys start with three clicks from full loose with their struts and move stiffer if needed," Cascio says. "On the back shocks, start at seven clicks from full loose and tighten as needed. The final settings all depend on a lot of factors, like chassis stiffness, tire age, track conditions, and so on. You want to run everything as stiff as possible without spinning the tires so you don't waste any energy. People want to set the car up real loose. You don't want dramatic wheelstands and excessive body movement backwards. Sometimes people need that, but you should try to avoid it. A great example is to look at a Pro Stock car and see how little the body moves. Just enough to keep the tire hooked."
Everyone has an opinion on springs. Some guys told us they are just there to hold the car up, while others had some more insight into how a drag-racing spec spring works. Moroso's Brett McLellan recommends the company's Trick Springs for Mustangs. They are available for the front and rear. "The Trick Springs have a lower spring rate and are a taller spring," he says. "When installed, they are compressed, and that stores more energy." That stored energy is released when the car lurches forward. The front end rises-much like the struts-and the spring helps fling the front end in the air. Springs are also used to vary ride height, and everyone agreed that while a lowered car looks great, in some cases it might hurt dragstrip performances. The idea is to transfer weight rearward, and a lower front end could hamper that chore if there is not enough tire or power to overcome the center of gravity.
The front end needs little help in order for a Mustang to be a track performer. The struts and springs are easily swapped out, and the only other major modification that enthusiasts perform is adding a tubular K-member and tubular A-arms. Along with those mods are also a coilover set of struts and caster/camber plates.
"Get weight off the front end," says Dario Orlando, whose company, Steeda, makes many components to lighten up the front of Mustangs. The amount of weight saved from a tubular K-member and A-arm setup can be as much as 67 pounds, says Martorella. He also says that swapping the front end in a Mustang could be done in a driveway in as little as three hours. Some added components to the front-end kit are a bumpsteer kit (to keep front tires parallel) and caster/camber plates (alignment adjustment to help steer the car straight at high speeds).
Cascio offers some suggestions for spring rates for front coil-over struts. He said, "We make a conversion kit to convert our struts to utilize a coil-over spring. Normally we suggest starting with a 175-pound spring. It all really depends on some factors, like if there is an intercooler, turbo, or blower up front, or anything else that alters the weight of the front end." There is a stigma in the Mustang market that sometimes the car doesn't transfer as well with the coilover-style struts. Cascio says the problem is probably sourced to having the wrong struts or strut adjustment, wrong springs, or even having the front end too low.
Getting weight off the front end helps your Mustang transfer weight better and accelerate down the track quicker.
Aftermarket Drag Race-Only Suspensions
The Mustang certainly benefits from a stout factory suspension system that works great on the dragstrip. There comes a time, however, when more traction and adjustability are required. It might be because the owner wants to stuff a large-size tire underneath the car for consistency or the power under the hood is over the top (is there such a thing as over the top?). If that's the case, then the aftermarket offers two types of replacement rear suspension systems-a ladder bar or a four-link.
The ladder-bar suspension is the simpler of the two as there are two bars that connect the rearend to the chassis. It is a single mounting point for each side of the rearend, and the bars are shaped like an A-arm. The ladder-bar mounts have a variety of holes to which the ladder bar can be bolted. These fixed mounting locations offer more or less shock to the tire on the launch. The ladder bars come in various lengths, with 32-inch and 36-inch bars being the most popular sizes.
Four-link rear suspensions are a lot like the '79-'04 Mustang rear suspensions in that the rearend attaches to the chassis through four links. The aftermarket four-link setup mounts straight (front to back), rather than angled inward like the stock upper control arms. "You have infinite adjustability of the instant center with a four-link," MacPherson says. "The instant center is the intersect point of the upper and lower four-link bars. It allows the car to lift the most weight and transfer it the best to the back of the car. It is all about transfer. Ladder bars have a predetermined instant center due to the length of the bars."
Ladder bars and four-links can be installed in stock-chassis Mustangs as well as what is called a back-half car. A back-half car is one where the rear subframe has been cut away and a new one has been installed. Usually the new subframes are narrower, allowing larger and taller tires to be installed. Perfect examples of a back-half car are the popular Outlaw 10.5 race cars. They feature stock-style front suspension systems with fabricated back-half framerails.
"Four-links are a thing of the past with real 10.5-inch tires and are mostly used now in big-tire cars [33x10.5W and larger slicks.-Ed.]," MacPherson says. Either way, no matter the horsepower, the aftermarket has something to help your Mustang stay hooked up on the track.