Editors' note, June 16, 2014: I was recently able to take a second look at the 2015 Subaru WRX STI, so we're updating the our track-centric first look to reflect new information about the available tech and daily driving experience.
Imagine for a moment that you're on your favorite driving road, ready for a quick and curvy blast, but instead you find yourself stuck behind some tourist who's slowing your ride to a crawl, thanks to his or her unfamiliarity with the road. Imagine the frustration that you'd feel; now imagine that the road is your favorite race track and that both you and the slowpoke ahead are both driving 300-plus-horsepower, all-wheel-drive, race-bred sport sedans. What a waste of speed! This was my first lap piloting the freshly announced 2015 Subaru WRX STI 'round Mazda Raceway Laguna Seca, my frustration increasing exponentially with each turn as I balanced trying not to bully the poor guy with wondering how bad of a slap on the wrist I'd get from our hosts for blowing past him at this no-passing-allowed exhibition event.
Just when I was ready to bend the rules, the slowpoke prematurely dipped into the pit lane, leaving me with a clear shot at the track's long front straight and a sudden outlet for the red mist that had been building over the lapping session. Perhaps it was this red mist that caused me to misjudge the braking point for the track's infamously tricky Turn 2 hairpin, but it was certainly the genius of the 2015 STI's revised symmetrical all-wheel-drive system that saved my bacon in the end.
Based on the newly announced Subaru WRX (and, ultimately, the Impreza sedan), the 2015 WRX STI is the hottest, fastest ride that the automaker is currently producing. Like the WRX, this is no mere performance package for the docile Impreza -- it's a whole new vehicle.
Peek through the functional hood scoop and you'll see the top-mount intercooler that chills and condenses the intake air that's being crammed into the 2.5-liter Boxer engine by the STI's turbocharger. That engine is virtually unchanged from the previous generation of the WRX STI and retains the performance as well as the Boxer burble that we loved in its last appearance. The engine also still feeds premium fuel into its combustion chambers by way of port injection, rather than the more modern direct-injection setup used by the standard 2015 WRX's new 2.0L. Given that, there should be no noticeable gains in fuel economy, but the numbers that you're probably interested in are the output, which is stated at 305 horsepower and 290 pound-feet of torque.
That power flows through a close-ratio six-speed manual transmission that is also largely unchanged from the previous generation, retaining its solid shifter linkage where the standard WRX moves to a cable linkage. This, along with a few improvements engineered into shifter mechanism, give the STI an improved shifter feel with better feedback than the WRX, which is a good thing. Enthusiasts will rejoice in knowing that the WRX STI will be made available only with this manual transmission; there's no automatic or CVT option.
The engine and gearbox may not have changed, but the rest of the vehicle around them certainly has, starting with the automaker's Symmetrical All-Wheel Drive system. Utilizing a combination of electronic and mechanical center differentials mated with yet a third planetary gear-type differential , the standard all-wheel-drive setup now defaults to a slightly rear-biased 41:59 torque split, but that split can vary continuously up to a lock of 50:50. Why two center diffs? Subaru tells us that the electronic differential allows finer control of the front-rear torque split based on the intricacies of yaw rate, steering angle, lateral-g, and more, while the mechanical differential is faster to react to changes in engine torque output. Together, they should create a system that is both sensitive and robust.
With power split between front and rear, it must next be split between left and right by a pair of limited-slip differentials: a helical-gear type on the front axle, and a Torsen torque-sensing electronically controlled limited-slip differential at the rear. On top of that, the 2015 STI features Subaru's new Active Torque Vectoring software, which uses bias braking to proactively split power between port and starboard when cornering. All in, I'm counting five total differentials shuffling power front to back and left to right.
Giving drivers control of that complex powertrain are the VDC stability and traction control system, the DCCD differential control system, and the SI Drive powertrain control system.
There are three levels of Vehicle Dynamics Control: The default is full traction and stability control, Traction mode (TRAC) disables traction and stability control but leaves the Active Torque Vectoring system active, and Off disables even the torque vectoring.
There are also three settings for the SI Drive throttle control system: Sport is interestingly the default setting for sporty driving, Intelligent uses a slightly less sporty throttle response for driving in inclement weather, and Sport Sharp (S#) is the most dynamic setup with the sharpest throttle response regardless of engine speed.
Finally, there's the Driver Controlled Center Differential, which features three automatic settings. Auto [+] emphasizes greater traction and is best for wet or slippery roads, Auto is the baseline setting for daily driving, and Auto [-] loosens up the vehicle's handling for quicker steering response and better rotation when cornering. If you don't like the automatic DCCD settings, there are six manual levels to choose from, ranging from Low, which is best for high-grip, corner-happy situations, to High (or Lock), which is best for slippery conditions or high-speed, straight-line stability.
That's a lot of settings to process. Thankfully, Subaru's engineers gave me a cheat sheet for the best settings: set VDC to TRAC (but not Off), SI Drive to S#, and DCCD to Auto [-] when you hit the track. On your favorite back road, leave VDC on and set SI Drive and DCCD to their default S and Auto settings, respectively. After a day of fiddling with the settings, I unsurprisingly found that the engineers knew what they were talking about.
Easier to wrap my head around were the chassis and suspension upgrades for the 2015 WRX STI. Simply put, the entire vehicle is stiffer. This includes the chassis, which boasts torsional rigidity that's 40 percent stiffer than the standard Impreza sedan, and the suspension, which is stiffer overall when compared to that of the outgoing STI model, with higher spring rates, stiffening plates, and more rigid bushings. The STI's steering is quicker than the standard 2015 WRX upon which it is based, and it retains a hydraulic power steering system, rather than making the jump to an electronic rack. Its rear suspension features slightly more rear toe-in, which further improves its turn-in responsiveness. And at the business end of that suspension are larger wheels shod with wider, stickier tires.
From the outside, the best way to tell a 2015 WRX STI from a lesser WRX is the massive rear wing that protrudes from the rear deck. Subaru tells us that this isn't just a styling choice; the wing contributes downforce at speed, increasing stability. On the bright side, it sits so high that you can see clear under it from the driver's seat, so at least it doesn't reduce visibility.
With the performance parts fully explained, I donned my helmet and hit the track. Immediately I noted that I enjoyed the STI's deeply bolstered seats, which also now featured a higher back and adjustable headrest. Pedal placement was ideal for easy heel-and-toe downshifts, the standard shifter gave great feedback and positive engagement, and cabin visibility is quite good. The flat-bottomed steering wheel was the icing on the driver-focused-cabin cake, with a thick rim, but small racy diameter. The STI is a car that is easy to drive, its cockpit fitting my 5-foot, 9-inch frame like a glove.
Armed with my knowledge of how the all-wheel-drive system worked, I knew that the DCCD and the rest of the alphabet soup were shuffling more power to the rear axle and outboard midturn to help with rotation, and then shuffling it back to a perfect 50:50 split for maximum grip as I rolled onto the throttle post-apex. I knew these things, but I didn't actually feel them happening. Earlier in the day, drivers groaned when they heard of the STI's Brake Override System -- a new unintentional acceleration deterrent that prevents the car from accelerating when both the gas and brake are depressed -- but the addition of this system didn't hamper my ability to heel-toe downshift, a maneuver that specifically requires pressing the gas and brake pedal simultaneously while shifting. The STI's safety net almost never shows itself when you're just going fast, which made me feel comfortable and encouraged as a driver to just go faster.