Dialing in a race car is a long and complicated process. We do it because of the satisfaction and frustration it brings, and, more importantly, for the friends we make along the way. If we claimed in this article that the parts we installed on Ron Burgundy, our Fox Mustang project, took us from wheelspin to wheelies, we'd be lying. Although these parts did solve some of the basic problems that prevented us from getting an accurate baseline, they represent the first steps in making this car fast and reliable.
In the Jan. '13 issue, we took the Fox Mustang to the Auto Club Dragway in Fontana, California, and ran some respectable 7.80s at about 90 mph or about 12.25 in the quarter. The car has a single 61mm turbo from a Hellion Street Heat kit on what is essentially a stock engine, a 3.27:1 gear ratio, and a good 4R70W transmission from Performance Automatic. Not too bad, but on paper the car should be able to run 11.70s at its current weight and horsepower.
Looking at the photos from the Fontana event, we noticed several problems with the attitude of the launching car. It would pull hard to the right, as evidenced by the right front tire rolling under as the driver counter-steered to keep the car straight, and it would bounce and unload the rear tires once the front end came down, indicating that the dampers (shocks) weren't controlling the springs. The result was a 2-second, 60-foot time with a lot of uncontrollable wheelspin and a Fox Mustang.
The solutions to these problems are relatively simple. Since the Fox Mustang has to be the most drag raced body in recent history, there are many companies with a lot of knowledge about how to dial in one of these cars. One such company is Maximum Motorsports (MMS), which employs guys like Jack Hidley, who know just about everything about these types of door-slammers. We gave him a call to get some solutions. We'll get to that, but first, a little theory.
Center of Gravity
Everything revolves around the Fox Mustang center of gravity (CG). If you placed a jackstand in the center of the car under the CG, it would be balanced in the air with neither the front nor rear tires touching the ground. The CG is a fixed position. Looking at the car from the side, the four-link's two upper and two lower control arms form a triangle that intersects at an invisible point called the instant center (IC). The term “instant” is used because as the car and suspension begin to move, the IC moves as well. As you raise and lower the car's ride height, you change the position of the IC. The same is true when you raise or lower the upper or lower control arms. Controlling the IC means controlling how the suspension rotates around the CG and how fast and hard the tires are loaded when the car begins to move.
On cars with a solid axle, there is an imaginary line extending horizontally from the contact patch of the rear tire to where the front-axle vertical centerline reaches the height of the CG. This imaginary line is called the neutral or antisquat line. Using suspension and ride-height adjustments, you can move the IC above this line to hit the tire with more torque, or lower the IC to soften the hit on the tire. The IC can also be moved forward (closer to the front axle) or rearward (closer to the rear axle), which affects the rate at which the load is applied. Generally, the closer the IC is to the rear axle, the quicker the load is applied.
This is the adjustable, 11⁄4 -inch- od x 0.250-inch-wall-thickness, heavy-duty, drag-race
The job of the sway bar is to keep the axlehousing from rotating up into the chassis on a
The MMS sway bar is also adjustable. As the attachment location moves toward the rear of t
The springs and dampers control the speed of the car’s pitch rotation, slowing down or spe
The Tokico dampers adjust both jounce and rebound at the same time with 7.5 turns of adjus
The front struts, now converted to coilovers, do it all. Using the adjustment collar, we c