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UPR Products ’79-’04 Mustang Suspension

Posted By: Evan J. Smith

UPR Products ’79-’04 Mustang Suspension


Written by Patrick Hill

Photography by the author


Drag racing a high-horsepower 1979-2004 Mustang with a manual transmission creates extra wear issues to watch out for that isnt a concern for automatic transmission vehicles. The harder launch of a manual-transmission car transfers more torque and energy to the rear suspension than an automatic car.

Team UPR has a lot of stick-shift racers. From 9-second Coyote Stock cars to the 7-second H-pattern class cars, our racers have pushed the limits of our suspension and earned countless class wins and championships in the process,” Sharad Raldiris from UPR Products explained. “They've shared a lot of their data and experiences with us, but one detail which surprised me was 9-second Coyote Stock cars are harder on their suspension components than 4-second (eighth-mile) Renegade/Ultra Street cars,” 

In particular, the lower control arm hardware on the body side has to be swapped out once or twice per season. Stick cars are violent on the launch hit. Slipper-style clutches soften the impact better than twin-disc street-style clutches, but both clutches are harder on the drivetrain and suspension than most popular automatics,” Raldiris added. “So, when a customer needs suspension for a quick/high-horsepower stick shift car, I treat it as if it's a 1,500-plus-horsepower race car. Essentially, this means we move to our Extreme Duty line of suspension.”

With turbos and superchargers becoming mainstays, achieving high horsepower levels is easier than ever. This creates problems because the engineers designing the Fox and Fox-4 Mustangs suspension and unibody structure never intended for it to see horsepower and torque near the 500 mark, let alone the 1,000-plus power levels adding boost easily creates. This changed how UPR recommends parts to its customers when they reach out looking for the upgrades necessary for their car.

It's so easy to make horsepower these days. There are a lot of people out there with destroyed torque boxes and they don't even know it. Any serious racer should inspect their car regularly and take note of any abnormal wear and tear,” Raldiris said. “This is particularly important when it comes to suspension components, suspension hardware, and the torque boxes on ’79-’04 Mustangs. Most parts will show fatigue before they fail, but you have to look!”

Our subject 2004 Mach 1 Mustang belongs to NMRA Circle D Specialties True Street and TREMEC Stick Shift Shootout competitor Kyle Miller. It runs the Mach I 4.6 DOHC with a single turbocharger helping the car make 1,000-plus horsepower at the wheels. Multiple years of racing this setup on the stock torque boxes. After the 2024 NMRA Spring Break Shootout, he noticed the Mach 1 pulling to one side on launch. His solution to this problem was the UPR ’79-’04 Ford Mustang Extreme Upper & Lower Torque Box Replacement Kit. The installation of this upgrade requires welding, which KM Performance and Fabrication in Zolfo Springs, Florida, handled. 

Follow along in the photos and captions to see what he found when the Mach 1 was up on the KM Performance lift, and where UPR Products came in to help give the 2004 New Edge Mustang the extra strength and rigidity it needed to handle those hard 1,000-plus-horsepower launches. 


After the pull to one side was noticed during a run, Kyle shut the car down and got it on a lift ASAP to find out what was going on. This is what he found. On both the body and rearend mount for the lower control arms, the bolt holes had started to elongate, allowing movement of the rear end to induce a pull under full throttle. Similar wear was found on the upper control arm mounts as well.


Further examination showed the factory torque boxes began to separate from their factory welds due to all the hard launches/hits as Sharad Raldiris from UPR had described to us. These pieces were never meant to withstand anywhere near the amount of power cars like Kyles produce, so only a matter of time before the separation would become dangerous and cause damage to the unibody structure. 


Side by side you can see how much beefier the UPR torque box is. While the factory box used relatively thin gauge stamped steel, the UPR box features fully welded construction with a thicker gauge steel structure and 1/4-inch thick steel for the lower control arm mount structure. The UPR torque box features ½-inch control arm mounting hardware, and multiple mounting holes to give racers maximum adjustment range for suspension tuning. UPRs 79-04 Ford Mustang Extreme Upper & Lower Torque Box Replacement Kit (PN 2016-100) comes with the hardware and cutting templates necessary for installation. These weld-in not bolt-in, so youll need the necessary welding and cutting equipment if youre going the DIY route here. 


The UPR upper control arm mount fits in place of the factory stamped-steel mounts that are spot-welded into the body. This piece will have to be cut and drilled out using a spot weld drill bit, and whatever combo of cutoff wheel and Sawzall works best with your skill level to cut away and remove the factory mounts. Like the UPR torque boxes, the upper control arm mount requires weld-in installation. 

 Before Kyle was running UPRs Pro Series single adjustable lower control arms on the Mach 1, though he converted to coilovers so the factory spring mount on the lower arms wasnt necessary anymore. The downside to the single-adjustable arms was to make adjustments the car had to be jacked up so the rearend could drop lower enough to provide access to the adjusters on the front of the arms. Part of the upgrade on the control arm mounts was also swapping in a pair of UPRs double-adjustable Extreme Series lower control arms. This provides more and easier adjustment to get the rear wheels centered in the wheel wells longitudinally and maintain optimal suspension geometry/travel. Also installed was a new set of UPRs Extreme Series double adjustable upper control arms (PN 2001-01-R).


If youre installing this yourself, youll need a high enough output welder, cutoff wheel, and Sawzall, plus a spot weld drill bit and multiple cutting blades for the spot weld drill to take care of all the factory spot welds holding the factory pieces in. Spot weld drill bits are easily purchased from most tool outlets. Lots of small metal pieces will be flying about too, so dont forget some eye protection. 


The UPR pieces come as bare steel. Before the installation, youll need to clean them of any oil residue and give them a good coat of weld-through primer before installation, especially on the inside so they dont start to rust from the inside out. Once installed, they received a final coating in black paint to protect them from the elements. The same was required on the upper control arm mount.


One other tool needed if youre installing the UPR Extreme Upper and Lower Control Arm Mount kit is a level to make sure the upper control mount is installed properly. If one end is even a few degrees off, the upper control arm geometry will never be right and youll be chasing your tail to get it adjusted so the rear suspension works properly. The UPR upper mount features the same ¼-inch thick steel mounting points to withstand the same stresses. The upper mount also features multiple half-inch hardware mounting points for the upper arms giving racers more adjustability for suspension tuning. 


With everything back together and ready for the first test runs. For a starting point, the length of the new upper and lower control arms was matched to the length of the old control arms. Then everything can be fine-tuned after track testing.



UPR Products 

(561) 588-6630 


KM Performance Fabrications

(813) 316-8602

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