When Subaru introduced the WRX Impreza it was deemed as one of the most performance-oriented four-door sedans with great aftermarket potential. The ensuing years saw the introduction of the WRX STi - Subaru's answer to the constant threat posed by the evolution of Mitsubishi's Lancer. As the market matures and opinions polarize, a clear champion has yet to emerge in this rivalry. Because of this competition, Subaru is constantly pushing the limits of both performance and regulatory compliance right off the assembly line. Car buffs, in turn, push these limits even higher. Indeed, the beauty of the STi is the engine's well-built bottom end. What's more, the bolt-on aftermarket options available for Subis make the STi an ideal daily driver and project car.
These are the shared sentiments of Philip Petracca, the owner of this '06 Subaru WRX STi. Petracca was looking for a daily driver and had to choose between the Mitsubishi and the Subaru. Seeing that his friends and acquaintances all arrived at the same conclusion, he decided against the EVO. This choice destined him with the most marvelous platform, perfected by Dr. Ferdinand Porsche and later Subaru: the boxer engine. This impressive flat design permits any set of two pistons on opposing crank journals to reach TDC simultaneously, resulting in increased torque and that distinguishable, throaty, Porsche-like sound that only a boxer engine can make. Add turbo boost to this already potent arrangement and the force is even greater. Increase the size of the turbo and yielding 460 hp at the wheels isn't so unreasonable. So goes the basic formula used to make this street-friendly brute a "bit" more than the average daily driver.
Petracca says, the development could be broken down into two distinct stages: bolting on aftermarket components and begging Geoff Racier at Full-Race to engineer a manifold and up-pipe that would provide sufficient exhaust flow and support the bigger turbo without cracking under the added weight. The first 100 whp on top of the factory supplied 240 whp came at a relatively small price and little down time. Finding the rest of the power was more difficult and lasted roughly 10 months, several of them spent pleading.
With the exception of the manifold and up-pipe, all of the modifications were done using bolt-on performance products from various manufacturers sourced by Petracca, installed by Straightlinetuning.com and tuned by Agile Automotive Performance of Fallston, MD. This made a fun project car because most of the amendments were made in increments, making it easier on the bank account and relationships. As a veteran of motorsports, Petracca found the use of bolt-on components refreshing following the challenges associated with his recent 800hp twin-turbocharged '03 Infinity G35 coupe development. Besides, the goal of this project was to build an exciting daily driver.
From its modest beginning of a simple turbo-back exhaust, this project mushroomed virtually overnight. While maintaining its driveability and reliability for daily operation with components from Samco and Snow Performance, the products from industry leaders like HKS, Forced Performance, Full-Race, APS Engineering and Cobb Tuning improved the weight-to-power ratio from 11.1 lb/hp to a stunning 7.5 lb/hp, as measured by factory supplied marketing information and dyno data.
The initial installation of Cobb Tuning's direct fit replacement 3-inch diameter stainless steel exhaust system screamed for more attention and power. The early response included an HKS Twin Power DLI II unit, which delivered optimum spark duration and maximum voltage output using the capacity discharge and transistor ignition methods combined to provide crisper throttle response and a smoother engine powerband. This dual method addresses both the low-rpm need for long spark duration and the high-rpm need for strong rapid spark.