Both '99 and '01 Cobras featured an IRS sprung with 470-lb/in coils, while the 2000 Cobra R wore 800-lb/in springs. The '03 Cobra coupe features 600-lb/in springs. Meanwhile, the '03 Cobra convertible sports familiar 470-lb/in springs in the rear.
There was much rejoicing among Ford enthusiasts when an independent rear suspension (IRS) was finally grafted onto the back of the Mustang Cobra. But, as with everything on Ford's famous ponycar, there was also immediate enthusiasm for modifying that long-awaited IRS.
Maximum Motorsports' IRS coilover...
Maximum Motorsports' IRS coilover kit is designed to work exclusively with Bilstein shocks, which have to be modified to accept the threaded sleeve and lower spring perch. "You have to have the body of the Bilstein grooved," Maximum Motorsports' engineer Ehren Van Schmus says, "and that's going to require the customer to send the shock back to us to groove it, or they're going to have to take a trip to their local machine shop. If they order the shock from us at the same time they order the kit, we will go ahead and groove the shock."
Maximum Motorsports has made a new contribution to the cause with the release of its Bilstein-exclusive IRS coilover spring and shock kit. The IRS kit follows hard on the heels of Maximum Motorsports' coilover kit for the solid-axle Mustangs. The two kits are similar, but the IRS pieces offer some distinct advantages of their own as well as a slightly different installation procedure.
We followed along with the installation of the new parts on David Simmons' '97 Cobra. David, of Austin, Texas, is the type of dedicated enthusiast who can't get out of bed in the morning without planning some new strategy for improving his Mustang. Last year he swapped his car's stock live axle for an IRS setup from a '99 Cobra, complete with Cobra R springs and a Torsen T-2 differential. He installed a Vortech supercharger as well, but recently removed it after deciding to nudge the Cobra more in an open-track/ road-racing direction. His car is well thought out and the modifications nicely executed, and he approaches his hot rodding with an engineer's appreciation for both theory and hardware.
David was working with Maximum Motorsports to test-install a preproduction version of the coilover kit, but the pieces shown will not vary greatly from the production parts, which will be available by the time you read this. David performed the work at a service bay at Motion Dynamics in Leander, Texas, using a floor jack and jackstands to raise the car, the better to approximate the average enthusiast's experience.
The coilovers offer two big advantages over the stock rear springs, and a couple small ones. "You are moving the spring more toward the centerline of the A-arm, or more within the 'A,'" Ehren Van Schmus, Maximum Motorsports' engineer and designer of the kit, says. "Because the way they [Ford] do that IRS, that one spring is hanging way out in front. That's pretty odd. You have a lot of bending and twisting in the control arm due to that, which adds a lot of friction in all the pivots.
Since the coilovers can be...
Since the coilovers can be adjusted for ride height, David Simmons measures the distance from the ground to the rear wheel lip before starting the job. This allows David to quickly return the '97 Cobra to his preferred ride height after the installation.
Maximum will match the springs...
Maximum will match the springs to the customer's car. "We'll probably have at least 10 different springs available in 25-lb/in increments," Ehren says. "We [basically] custom-tailor the spring rate to whatever that customer is doing." David's Cobra illustrated the range available. "We want to provide the same spring rate at the wheel with the coilovers as we do with the conventionally mounted spring," David says."I have 800-lb/in Cobra R springs. It calculates to being a 475-lb/in coilover spring."
Most of the work to install...
Most of the work to install the coil-overs centers around preparing the parts for installation. First, press out the factory crush pin in the lower shock mount of the Bilstein and remove the bushing. A stronger polyurethane replacement bushing will be part of the kit.