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.
The Watt’s-link pivot uses a Delrin bushing on its mount for controlled movement with zero deflection. Notice the double-shear arrangement on the center pivot bolt. This adds significant strength and plenty of safety factor to the design. All critical points of the Xtreme Grip kit have a torque spec, but pay special attention to the Watt’s-link differential-cover pivot-bolt spec since it needs tightening, but not too much.
Using the factory diagonal brace bolts, install the Watt’s tower bracket to the driver-side framerail in the location of the original brace bolt holes. Although not necessary, this bracket can be welded in for the ultimate in strength and rigidity.
Begin with the Watt’s link at the lengths delivered and adjust them if needed to center the axle. The new diagonal brace bolts into place afterward. The ability to choose from a number of center pivot hole heights is key to tuning the handling of the rear suspension. The higher holes stiffen the rear suspension, and the lower holes soften it allowing adjustment of grip to get a neutral-handling car. CorteX suggests starting in one of the middle holes.
Since this is the street kit, polyurethane bushings are used at the outer attachment points of the Watt’s links for NVH control. The inner attachments at the pivot are Heims for precise movement. The diagonal brace (right) is length-adjustable on the driver side for possible minor adjustment, ensuring fit regardless of tolerance stack-up or production tolerances. The passenger side is a solid mount.
The last piece installed for our Street kit is the original 19mm antiroll bar and its factory endlinks. It’s perfect for dual-duty street/track cars, but more aggressive cars can opt for upgrades per CorteX’s recommendations.
To ensure the rearend housing is centered, choose a reference point that is common on both sides and measure to the brake rotor. If the rotors are used as a reference point, make sure to fully install two lug nuts on each side to ensure the brake rotor is flush with the axle hub. Adjust the Watt’s links as necessary to center the axle to within 1⁄16-inch.
Compared to the rear, the front portion of the Xtreme Grip kit is a super-quick process. First remove the wheels and unbolt the strut from the spindle.
Since we’ll be installing CorteX’s caster/camber plates, the factory upper strut mount is removed via the bolts on top of the strut tower.
Like the rear coilovers, the fronts are custom-valved, single-adjustable Koni Sport and are shipped assembled with the caster/camber plates from CorteX. For the Street kit, the Eibach springs are 400-450 in-lb depending on the model of Mustang (GT vs. GT500). The really cool part of these coilover struts is the offset that allows 10.5-inch wheels with 315 tires with zero clearance issues!
The one upgrade we added to our base Xtreme Grip street kit is the optional Eibach front antiroll bar. This CorteX-spec bar is three-position adjustable and specifically suited for use with the Xtreme-Grip kit.
We also opted for CorteX’s adjustable endlink. This link allows the preload to be taken off the bar while corner-weighting the vehicle. Constructed of high-strength aluminum, and fitted with stainless-steel misalignment bushings, it also makes slight adjustments to the front bar possible. Note we started with the endlinks in the middle mount hole on the Eibach bar.
With everything bolted together and all torque specs rechecked front and rear, we dropped the Mustang down and set the alignment with a Longacre kit. We went with 7 degrees of caster, -2.5 degrees of camber, and a 0-degree toe angle.
Look at that meat! We can fit a 10.5-inch CorteX CX14 wheel with 315/30 Nitto NT-01 rubber on all four corners now, while still maintaining a factory turning radius!
Here’s a peak at how much clearance the relocated CorteX coilover offers while still improving the front suspension geometry. You simply can’t do this with most coilover kits.
If you’re looking for an affordable way to get that much wheel and tire on your car after the Xtreme Grip makeover, CorteX also offers these custom-spec, one-piece Jongbloed (www.jongbloed racing.com) Series 700 wheels designed for perfect fitment with the Xtreme Grip kit.
Check out CorteX Racing's Youtube channel (www.youtube.com/cortexracing1) for an amazing in-car HD video of a CorteX equipped Spec Mustang attacking Laguna Seca. It may be hard to believe, but the car in this video is mechanically identical to our test car other than long-tube headers, an X-pipe, full Heim joints on the Xtreme Grip system, and a gutted interior—that's it! So yes, you can have this level of grip in a daily drivable S197! Turn up the sound loud for this one!
The ride isn't as intense, but also check out the video of our test car getting its suspension installed and then tested on Sonoma Raceway there as well!
|Maximum Lateral Acceleration, left, Turn 3
|Maximum Lateral Acceleration, right, Turn 7
|Average Lateral Acceleration
|Maximum Apex Speed, Turn 6
|Best Lap Time
We documented our results with a datalogger, and as you can see, the lateral grip increased by 17.4 percent with the Cortex suspension, and lap times dropped by 7.06 seconds per lap.
Horse Sense: If the Cortex gear interests you but you don't own an '05-and-up Mustang, don't fret. The company also offers parts and complete suspension systems for '79-'93 and '94-'04 Mustangs.