Frankly, nothing was overlooked when developing the KR, from shift-throw ratio of the Tremec six-speed to a unique KR-only alignment spec. The wheels, made by Alcoa for Ford and Shelby, feature more radial and lateral stiffness, while the Goodyears that are wrapped around them-P255/45ZR18s in the front and P285/40ZR18s out back-were specifically designed for the KR with revised rubber compound and steel-belt construction.
The KR's ABS and traction control systems were both remapped to take full advantage of the new tire, wheel, and suspension packages. Behind those sweet forged wheels are Brembo 14-inch rotors with fixed, four-pot calipers up front, and 11.8-inch rotors with single-piston calipers at the stern.
Rounding out the performance improvements is a completely redesigned exhaust system that features a revised crossover, all stainless steel construction (where most of the KR's 22-pound diet over the GT500 came from), and smaller, more cylindrical resonators utilizing the '08 Bullitt Mustang glasspack tips. An elevated axle-vent reservoir, which prevents expulsion of gear oil during extreme performance driving, is found at the rear, coming straight from experience gained in the FR500C racing program.
Get In, Sit Down, & Hold On
So what's it like climbing into the leather-clad cabin of the KR and putting the most powerful production Mustang ever built through its paces? For starters, we had ample seat time to evaluate the KR on the surface streets and nearby highways of Salt Lake City. Upon walking up to the car, the more muscular overtones were immediately evident. We absolutely loved the hunkered-down stance and revised aero package. Admittedly, we wished the production car kept the concept's 20-inch wheel package, only because the S197 wheel openings are so big, but we got earfuls of engineer-speak about unsprung weight, braking forces, and so forth.
Once inside, the first thing that put a grin on our faces was the exhaust note that greeted us upon twisting the key. The enhanced sound quality of the exhaust was a welcome change to the usually muted OE systems found on modern Mustangs. It'll be hard to beat this setup in the aftermarket. During driving maneuvers, the exhaust was right there at the back of the car, but not overbearing, and without a hint of drone. But all it took was a tickle of the right foot to bring the exhaust tone up to announce our arrival (hey, even a guy on a sport bike gave us a thumbs up when we revved the engine at a stoplight).
Speaking of revving, the KR loved to do that all day long. From a nice, smoky burnout to high-rpm freeway passes, we found ourselves quickly climbing the tach. The clutch effort in the KR was very much like the GT500's, with the same twin-disc clutch setup between the 5.4 modular and the Tremec six-speed. This allowed us to even enjoy (if you can call it that) some stop-and-go traffic without praying for an automatic-heaven forbid-or the nearest off ramp to take a leg break.
The KR's shifter, topped with a classic white ball, is from the Ford Racing parts bin and features a 25 percent shorter throw than the GT500's. Frankly, this baby needs to be the stock shifter in every new Mustang as far as we're concerned. If you've ever missed a gear due to the rubber-hose-in-a-box-of-rocks-feel shifter, you owe it to yourself to upgrade the handle in your S197 to this unit. It'll make even your daily drive to the office more fun-we guarantee that.
The suspension on the KR, while more firm than the GT500, didn't beat us up, even when spending serious time in the driver seat. When we first saw the lowered stance we thought we'd be needing kidney belts, but instead were pleasantly surprised that the engineers did a top-notch job of recalibrating the shocks and struts, sway bar diameters, bushing durometers and, of course, the spring rates themselves. It's a very compliant ride that will work on the freeway or your favorite corner at Miller Motorsports Park (which we soon realized with track time the following day).