2008 Subaru Impreza WRX STI - Power Check!

AccessPort Tuning: Jon Buenas

Baseline
Pros
The newly designed '08 Subaru Impreza STI, powered by the infamous 2.5L boxer engine is rated at a factory 305 hp and 290 lb-ft of torque. The '08 model continues the Subaru legacy as its rally proven symmetrical all-wheel-drive system and turbocharged powerplant have been a successfully lethal combination in the world of automotive performance.

Cons
It's a known fact that the new era of automobiles sold in today's market have become more technologically advanced into both electronics and engine efficiency. The news is a promising forecast for the average daily commuter but a nightmare for those looking to increase horsepower by simply slapping on a few bolt-on parts. The '07- '08 Subarus (and some 06 WRXs) were tuned from the factory to pass strict emissions testing, often sacrificing the true potential of the EJ25 engine. "They run stoichiometric air/fuel ratios (14.7:1) through peak boost and to about 4,000 rpm, which is great for fuel economy but BAD for power and driveability," HB Speed owner and tuner Jon Buenas says. The '07-'08 ECUs also have multiple timing tables that, upon certain situations, add, subtract, or even multiply the timing values the motor runs. There are tables within the factory ECU that can add to themselves and then add to the total timing (bad). There are also timing floors where the total timing value cannot go below a certain amount, which are also considered bad. What does this all mean to a Subaru owner looking to bolt on a few go-fast parts? "If the vehicle is not properly tuned, the ECU can take the tuners intended timing value (lets say 11) degrees at peak torque and if it so sees fit (using knock feedback and other algorithms) add 8-10 degrees (effectively running 19-20 degrees). The problem is the ECU is not quite fast enough to pull out that timing if it knocks hard (which it would) and eventually would blow the motor up," Buenas says.

Dyno Test Results
With numerous horror stories spread throughout the community of Subaru '07-'08 STI models with piston ringland problems, and most recently '08 turbocharged Subarus being recalled for engine knocking noise, we took special precautions in running our baseline dyno pull to get our preliminary numbers. The '08 STI rolled the dyno to a tune of 223 whp and 250 lb-ft of torque. Note the power numbers we list throughout this test are given in wheel horsepower and not to be mistaken for flywheel rated power.

Product
AccessPort unit, user guide, USB cable, OBD-II connector, software CD

Tune And Remap Ecu Time
Full day process

Cobb Accessport
ProsCobb Tuning recently released the newest version of their AccessPort to work in conjunction with the '08 STI. The AccessPort is a simple to use hand-held device that enables Subaru owners to plug the controller into the factory OBD-II port. Within minutes, one of the pre-installed performance maps or a custom map can be easily uploaded into the vehicles ECU to alter and optimize air/fuel ratio, ignition timing, and boost. Added features when using the ACCessPORT include the ability to monitor fuel economy, troubleshoot ecu codes, estimate 0-to-60 and quarter-mile times, and even monitor real-time data as you drive around town.

ConsSimply bolting parts on the '07-'08 STI and neglecting to run the proper ECU tune can spell disaster for your engine. Many Subaru tuners recommend a reflash or stand-alone fuel management system for the ECU, prior to making any modifications as many stock '07-'08 turbocharged Subaru's have been known to blow up on occasion. Keep in mind as you begin to modify your engine that each part will change the factory tuned ignition maps and air/fuel ratio, some more than others.