Christopher Campbell Technical Editor
November 7, 2013

Some aftermarket performance companies are founded out of a driving passion to create better products for Mustang enthusiasts to improve their street cars. Others form out of a desire to push hot rodding and racing to new limits. When those passions and desires fuse under one roof, the result are products that perform well on the street and excel on the racetrack.

One such young company is CorteX Racing. It was officially founded in 2009, but its product designs have been brewing since 1999, when Filip Trojanek began taking a serious interest in road-course performance with his '66 Mustang. When he couldn't find the level of parts he was after, Filip decided to engineer the parts himself.

We use engineer in the purest form of the word too. There's a reason CorteX's unofficial motto is “everything engineered.”

Filip is life-long car nut who holds a bachelor's degree in mechanical engineering with a focus on structural mechanics from Oregon State University. He's designed everything from systems for semiconductor manufacturing to space flight equipment for Lockheed Martin, chemical weapons demilitarization, and even nuclear power component design and analysis.

To say he's a stickler for details and perfection is an understatement. He's in charge of designing and evaluating everything that CorteX produces, and he won't put the company name on a product unless it's proven with engineering tools like Finite Element Analysis, and further proven with real-world racing.

In the early days, as Filip became faster on track, that '66 Mustang became the ever-evolving testbed for new suspension pieces built with a focus on achieving American LeMans-level performance in a street-legal car. Now known as Xecution, that Mustang can generate cornering forces of 1.6g static and 2.2g peak. That's more than many supercars. Plus, it's been driven over 200 miles to events and then back home after besting competitors with six-figure budgets.

Needless to say, that kind of performance turned a lot of heads at Sonoma Raceway, Filip's home track. As such, he was approached by a couple of SN-95 Mustang racers who wanted to take their cars to the top level of American Iron Extreme racing. Filip used his experience to create parts for the SN-95 chassis. Both of those cars now regularly set and break their own class lap records at Infineon, Thunderhill, and Laguna Seca.

With his phone beginning to ring, Filip realized it was time to begin creating full suspension systems for the more prevalent modern Mustang track cars. The first Fox and SN-95 systems were pure race stuff, and they worked well. However, when inquiries for street suspensions poured in, Filip decided to make some minor alterations to remove some of the harshness and simplify installation. Using the knowledge gleaned from racing, Filip developed the Xtreme Grip line of suspension systems that cover all generations of Mustangs (excluding the Mustang II). The S197 version offers the highest level of performance with the least amount of work, as those cars offer the most stable and easily upgradable base platform.

So how good is the S197 Xtreme Grip system? Well, it's the only suspension system offered on the ultra-high-end, 1,000-plus-horsepower Shelby Mustangs. That storied company tested it, pronounced it the best they ever tried, and now carry a Shelbyized version of the Xtreme Grip system with their proprietary tuning changes. In the racing world, the off-the-shelf Xtreme Grip Track package is now the required suspension system for the newly formed Spec Mustang Series.

Of course we never just listen to hearsay, so we decided to put one of CorteX's Xtreme Grip packages to the test with a true before-and-after track test at Sonoma Raceway. We were blown away by the transformation. CorteX created an an incredibly effective, pure-bolt-on suspension package. The amount of grip and corner speed possible with an otherwise stock car is mind boggling. And somehow it's still a weekend bolt-on project you can do at home. This is legitimately how you can go from modest to supercar-level handling in your Mustang.

We handed the keys over to racing driver Colin Sebern for our before testing laps. Despite the great wheels and tires, the Mustang wallowed vaguely through the corners and ran middle of the pack in Group 3 for a handful of laps before Colin had to pull in due to severe brake fade. The in-car datalogger recorded peak lateral acceleration of 1.107 g left (Turn 3) and 1.096 g right (Turn 7) for an average of 1.102 g. The max apex speed (Turn 6) was 69.76 mph, and the best lap time was 2:05.09 minutes.
So here’s how we go from commuter to track star. This is the Xtreme Grip kit for S197 Mustangs, and it’s a thorough end-to-end makeover that replaces everything other than the rearend itself! Our test car has the Street version that pairs urethane endlinks with Heims to mitigate noise, vibration, and harshness. The race version is identical, but with full Heim endlinks and little concern for NVH.
Our first step is to remove the differential cover and let all the fluid drain out. This is a great time to upgrade to better gear oil, but don’t forget the Ford friction modifier.
The rear antiroll bar and its endlinks are removed next. Since we have the 19mm bar, this is the one stock part we will be reusing. CorteX’s testing has shown that this bar pairs perfectly with the Xtreme Grip system in street applications. The Watt’s-link system does not need a heavy rear antiroll bar to perform well.
Since we opted for the full Watt’s-link conversion, the Panhard bar is removed. The coilover-only upgrade from CorteX is compatible with a Panhard bar if you want to upgrade in stages.
The stamped-steel, diagonal Panhard-bar brace directly above the bar gets the heave-ho as well since it impedes clearance for the Watt’s-link bracket.
CorteX’s finely CNC’d differential cover incorporates the Watts pivot mount to eliminate flex, and the underside has robust ribbing to support the cornering loads. Plus, the multiple mounting options for adjustment of the rear roll center make balancing the car quick and easy. The race and street parts are the same, so ports are cast in for plumbing a differential cooler and temperature sensor.
Make sure you have support under the axle whether it’s on a lift or jackstands, because the LCA’s are unbolted next. Keep track of the stock bolts, though, since they will be reused. Also, this is a great time to remove the stock cast-iron weights from the top of the rear lower-control-arm brackets.
The first Xtreme Grip parts installed are the driver- and passenger-side lower control-arm brackets. The driver side is identified by a bend located about halfway up the rear attachment backstrap. A stock bolt paired with an internal spacer for crush strength is used on the lower bolt, while a new Grade 8 is supplied for the top.
The tubular Xtreme Grip lower arms are installed next. CorteX sets the length before shipping, so no adjustment should be necessary to bolt them in with the stock bolts at the front and new Grade 8 hardware at the axle. Since our kit is the Street version, it uses a polyurethane front bushing to minimize the NVH into the interior. Note we used the upper bolt hole at the rear—that’s the preferred setting for street/autocross/road course traction, while the lower would work better for drag racing. It’s a quick switch at the track!
The axle connection of the lower arm is a Heim joint supplied with machined, stainless-steel angle-correction spacers. The long spacer should be located inboard at the rear attachment point. Using these joints at the rear will control the motion of the rearend without unwanted deflection.
With the lower shock bolt removed, the stock coil springs will drop right out when the axle is lower sufficiently to unload them. The upper and lower rubber isolators are also removed. Many heavy stock parts are replaced with much lighter components, reducing unsprung weight significantly.
Using the factory lower shock mount, this bracket with a Grade 8 bolt will create the lower mount for the Xtreme Grip coilover conversion. A new longer bolt is included with the bracket, which is long enough to reinstall the antiroll-bar nut with the bracket in place. The brackets position the coilover shock such that wheels up to 11 inches wide and 315mm-wide tires will fit the rear of the car with no interference.
The coilover upper mount uses this crush spacer to center it perfectly in the factory upper shock hole and allow full torquing of the mounting bolt.
After unbolting the top mount for the factory shock from inside the trunk, the mount is slid into the hole. Some excess seam sealer may need to be removed so that the coilover mounting bracket slides into place without forcing. These brackets slightly relocate the coilover mounting position to ensure sufficient clearance for 18x10.5-inch wheels and 315mm tires. The bracket is designed to properly distribute the coilover loads into the unibody mounting pad. Years of testing on CorteX-prepped race cars has proven the design’s extreme durability.
We opted for CorteX’s standard street coilover package, which consists of CorteX-spec, custom-valved, single-adjustable Koni Yellow shocks and 250 in-lb Eibach springs. For more aggressive setups, custom-valved, multi-adjustable JRi, Penske, or Ohlins shocks are available as well.
Using a sharp knife or razor blade, trim the factory bumpstops to allow for sufficient suspension travel after lowering the ride height. Don’t remove them completely though.