2015 Subaru WRX STI (© Subaru of America)Click to enlarge picture

Using a combination of solid engineering and shrewd development, Subaru has produced an impressively balanced and potent performance car in the new WRX STI.

Sharper than ever, a new iteration of the vaunted Subaru WRX STI launches this spring in the wake of the restyled and re-engineered 2015 WRX. The STI jumps out of its stablemate's slipstream with a full array of systems, technologies and refinements that raise its handling prowess and proficiency to new heights. This new WRX STI achieves the singular feat of combining the incomparable feel, razor's edge handling and fiery urge of the original STI with unprecedented comfort, refinement and even practicality. It is arguably the most capable and versatile performance car you can find — and it's sturdy and reliable to boot.

View Pictures:  2015 Subaru WRX STI

The key to this transformation, as always, is a solid foundation. Made with about a third more hardened steel, the new body shell is stronger by about 40 percent in torsion and by 30 percent in bending than its predecessor. It is also only 21 pounds heavier, in spite of added equipment, thanks in part to a new aluminum hood. Other aspects of the STI's transformation include improved visibility brought by stronger, narrower front roof pillars, a lower dashboard and a more sloping windshield with its base moved forward by eight inches. Overall length is up by only 0.6 inch, but the wheelbase has grown a full inch and rear legroom has gained almost two inches. The trunk is now a full 12 cubic feet in volume, with 60-40 split-folding rear seat backs for expansion. And the big rear spoiler? It's functional and perched so high that it doesn't impede visibility through the rear mirror.

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Model lineup
As with the new WRX, Subaru decided to concentrate all resources on designing the new STI as a sedan only — the favorite choice for the previous generation — leaving out the hatchback. Subaru's "performance flagship" starts out better equipped than ever with all handling and performance elements standard, plus the expected array of comfort, infotainment and safety accessories and amenities, including a rearview camera. The optional Navigation package combines a 6.1-inch touch screen and voice-activated controls, a Harman Kardon premium audio system, Bluetooth phone and audio integration, satellite radio and most digital connectors.

Limited versions get 18-inch BBS alloy wheels, leather seats with power adjustments for the driver, a power moonroof and so-called welcome lighting. The Harman Kardon audio system is standard and navigation is still optional, along with keyless entry and start. Only a thousand units of a special Launch Edition of the STI will be offered, all painted in Subaru's traditional World Rally Blue Pearl and equipped with gold-painted BBS wheels that will remain exclusive.

Read:  2015 Subaru WRX: First drive review

Under the hood
Back for a return engagement is the STI's proven 2.5-liter turbocharged horizontally opposed 4-cylinder engine that can dish out 305 horsepower at 6000 rpm and 290 lb-ft of torque at 4000 rpm. It has a nice, round burble at idle and makes music as the revs climb, some of it channeled into the cabin by a "sound creator" for sheer aural pleasure.

The STI's boxer engine is mated exclusively to a 6-speed manual transmission. There is no optional continuously variable transmission for this top dog, unlike for the WRX. The revised manual gearbox also stays true to a parallel-shift linkage instead of the cables used on the WRX. Shifts are neat and positive, with a solid-feeling lever. Launch Edition variants are equipped with a shorter-throw shifter that is otherwise optional.

Changes made in the engine control unit to sharpen response are immediately obvious. The STI feels much livelier, even at the SI-Drive controller's mildest setting, dubbed "Intelligent." Twist the console-mounted knob to the left and you get quicker reactions to throttle input in Sport mode. I found no need to select Sport Sharp, even in brisk driving on a tight, twisty road. That mode is for track sessions, for which the STI has been specifically designed and developed.