2006 Subaru Impreza WRX/STI

The enthusiast public remains nutty for Impreza WRXs and Mitsubishi Evos. Internet blogs buzz for months with rumors of even the tiniest upgrades. So let this serve simply to confirm the scuttlebutt that, yep, the 2006 Impreza lineup gets a horsepower increase of--drumroll please--eleven! Sad to say, none of the newly foaled ponies will be pulling the top-shelf WRX STI model, and only three of them are teamed to the cooking WRX. The other eight go into the workaday 2.5i sedan and Outback Sport wagon models. Still, a horsepower is a horsepower, and we'd rather have more than less.

None of this qualifies as breaking news on the engineering front; these engines appeared first in the 2006 Forester. The base car gets an electronic throttle and a swirl-inducing variable-valve lift system that fattens the torque curve considerably (without changing peak torque of 166 pound-feet) and yields 173 horses. The WRX ditches its rally-champ homologation 2.0-liter turbo in favor of the Forester XT's 2.5-liter--certain to be the subject of much blogchat--bumping horsepower to 230 and torque to 235 pound-feet (up 18). Real-world fuel economy is also expected to rise just a smidgen.

All Imprezas get the new corporate airplane face, which works better on this lower-nose car than on the high-rise Tribeca. New headlamps, taillights, and bumper fascias also are revised. Some sheetmetal was massaged to improve high-speed aerodynamics of the World Rally Championship race cars. (The series forbids altering the production-car bodywork above bumper height). The air flows so well over the resculpted nose that the smaller WRX hood scoop provides sufficient cooling for the STI's big intercooler. A new black roof-vane spoiler works like the Mitsubishi Evo MR's vortex-generating fins, grabbing high-speed air and redirecting it to help push down on the gigantic trunk-mounted wing and improve high-speed stability. A rear diffuser helps clean up the air exiting from under the car.

Mechanically, the STI gets a new center differential that employs an electronic, driver-selectable lockup clutch and a torque-sensing mechanical limited-slip device that can react much more quickly than the electronically controlled LSD. The natural torque split is revised to 41 percent front, 59 percent rear (up from 35/65). While Subaru offers no stability control system yet, the Tribeca's steering angle sensor is fitted to the STI and used to better inform the center differential electronics when to lock and release. Finally, carbon-reinforced synchronizers smooth shifts into fourth, fifth, and sixth gears.