The WRX STI dominates the spotlight when Subarus are on display. Bench warming on the sidelines is the underappreciated WRX. Overshadowed by the STI's factory-performance prowess, the WRX receives little attention when it comes to tuning. With the release of the 2008 WRX, that attitude is shifting.

Subaru of America (SOA) and Subaru Performance Tuning (SPT) approached the design team at Advanced Engine Management (AEM) in Los Angeles, California to brainstorm, build and tune a 2008 Impreza WRX. Always up for a challenge, AEM gladly accepted the opportunity to work on the latest Impreza. When the brand new chassis arrived at the shop, AEM technicians went straight to work on the GHB chassis.

Get This Party Started

The first WRX on US shores came with a smaller-displacement engine while the STI came equipped with a much-larger 2.5-liter mill. Starting in 2006, the WRX received a displacement increase to 2.5-liters as well. AEM prepped the factory-fresh EJ255 boxer engine with a host of enhancements. Starting with the exhaust plumbing, AEM installed a Harman Motive uppipe to increase the exhaust flow to the turbocharger. A ball-bearing Garrett GT3582R turbocharger replaced the anemic factory snail atop the uppipe. A Harman Motive downpipe was bolted to the exhaust housing to channel spent gases to a custom b-pipe and a stainless-steel SPT exhaust system.

To filter the air ingested by the turbo, AEM designed an intake system featuring a Dry-Flow filter element. Once the turbo has done its job, the compressed air flows through custom intercooler piping to the Harman Motive front-mount intercooler to be chilled. From the intercooler, the compressed air makes its way to the reverse-mounted intake manifold.

Injected Performance

As the compressed intake charge reaches the intake ports, a quartet of Deatschwerks 850 cc/min injectors spray fuel into the combustion chambers. They receive a steady supply of VP Racing 110-octane race fuel thanks to a Walbro 255-lph in-tank fuel pump. To regulate fuel delivery as well as ignition timing, a plug-and-play AEM engine management system (EMS) replaced the factory ecu. An AEM Tru-Boost controller limits boost pressure to a maximum of 26 psi. To chemically intercool the air and fuel mixture, AEM supplemented the fuel system with its water-injection system. A second water-injection system was plumbed into the front-mount intercooler to provide additional cooling. The mixture of water and methanol help to effectively raise the octane of the air-fuel mixture, allowing additional ignition advance and increased boost pressure. Strapped to the rollers of a Mustang AWD dynamometer, the WRX produced 449 horsepower and 403 lb-ft of torque. That's an increase of 250 horsepower over the baseline pull of 199 horsepower made on this same dyno.

Wheels In Motion

To handle this significant power increase, driveline improvements were in order. Power generated at the flywheel is harnessed by an SPT twin-plate clutch. The clutch transfers power to the input shaft of a six-speed STI transmission. An STI also donated the differentials that split the power between each set of Volk Racing GT-V wheels. These 18-inch rollers were wrapped with Toyo Proxes R888 competition radials in a 245/40R18 offering. With the enhanced driveline and rolling stock in place, the WRX has the grip needed for all-out performance. To maximize handling, a JIC Magic FLT-A2 coil-over suspension lowers the center of gravity and emboldens the stance of the car. The coilovers also help to control the amount of suspension dive realized during hard braking. To bite into the asphalt and shed speed, the front brakes received an upgrade to Prodrive 4-piston calipers clamping down on Prodrive brake pads while 330mm Prodrive rotors replaced the factory discs.

Interior Design

Inside the cabin, a unique seating arrangement distinguishes this WRX from the rest. A Sparco S-Light carbon-fiber race bucket holds the driver in place, while a Sparco Circuit Pro seat positions the front passenger. The rear bench seat was modified to accommodate a single Sparco seat for a third occupant. Each seat was equipped with a set of Sparco 6-point harnesses to hold the occupants in place. AEM then called upon Sinister Race Cars to weld in a 6-point cage to stiffen and reinforce the cabin as an added measure of safety. In the center of the dashboard, AEM digital gauges mounted in a custom carbon-fiber panel monitor engine vitals. Steering input is facilitated through a Sparco model 383 steering wheel. SPT pedals guarantee sure-footed driver input.

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