Pete Epple Technical Editor
July 5, 2012

It didn't take long before Mustang enthusiasts found the limit of the SVT Cobra's IRS. A set of sticky tires and aggressive launches resulting in wheelhop has prematurely ended the lives of many independent rearends. This is a huge problem when it's so easy to make big power with a Four-Valve and some boost.

It takes a certain amount of finesse to get power to the ground through the Cobra IRS. Anyone who's driven a modded Cobra can tell you it doesn't take much throttle application to induce wheelhop. With a solid axle, wheelhop is almost a non-issue, but with an IRS, when the rear tires fight for traction, the grip and slip of the tires can wreak havoc as they try to find traction.

Carl McGill is the owner of this Screaming Yellow '04 Mach 1, which has been upgraded with an '03 Cobra IRS. Besides its suspension upgrades, McGill's Mach has a 1.7-liter Kenne Bell Twin-Screw supercharger, full exhaust, JLT cold-air intake, and custom tune from Big Daddy Performance (Lakewood, New Jersey). This daily driver laid down a very respectable 504 rwhp and 446 lb-ft of torque. Unfortunately, getting that power to the ground resulted in significant wheelhop in First and Second gear before it finally hooked up in Third.

"First and Second gears are just about useless unless you baby it," comments McGill. "It's not an easy car to drive aggressively on the street. As soon as the tires start to spin, you have to be out of the gas, or wheelhop starts." To remedy this, we turned to Maximum Motorsports and QA1.

Maximum Motorsports has a full line of components designed to fortify the IRS and greatly reduce wheelhop, leaving you with the ability to plant the tires harder on the street or track without the fear of killing your IRS. Maximum sent us its Super Street/Competition IRS Grip Package, which consists of subframe bushings, upper and lower A-arm bushings, differential bushings, adjustable swaybar end-links, adjustable tie rods, and all of the removal and installation tools to make quick work of swapping the bushings.

We finished off the IRS fortification with a set of double-adjustable QA1 rear shocks. The TD707 shocks have 18 compression adjustments and 18 rebound adjustments for a total of 324 settings per shock. This may sound overwhelming, but QA1 does a great job of providing base setting for different styles of driving, which we'll get into later.

When it comes to the IRS, there is nothing quick or easy about it. With this in mind, we turned to Big Daddy Performance in Lakewood, New Jersey, to handle the install. But before we ripped out the IRS, we headed to Englishtown Raceway Park for a few 60-foot passes to establish a baseline for our testing. Once the Maximum Motorsports Grip Box and QA1 shocks were installed, we headed back to the track.

Follow along as we add some strength to this IRS Mach 1, and be sure to check out www.muscle mustangfastfords.com for exclusive photos and video of our track test.

On the Street

"Before the Maximum Motorsports and QA1 stuff, the car was balanced and handled well, but wheelhop was a serious issue in First and Second gears," explains McGill. "When I got the car back, it was totally different. The handling characteristics of the rear suspension were night-and-day better than before. Although wheelhop is still present when you're hard on the gas, it's much more controllable than before. When the car gets sideways, it recovers much better than before, and with less effort. The only downfall is the rear suspension is now much better than the front and the two feel disconnected. The difference in handling made it a new car, and it's amazing to see how much bushings and shocks can do."

Photo Gallery

View Photo Gallery