The 04 STI engine represents the pinnacle of Subaru’s horizontally-opposed engineering, specifically harnessed within the 2004 Subaru Impreza WRX STI. This model year marked a significant evolution for the legendary 2.0-liter turbocharged boxer, blending refined power with track-focused capability in a production street car.
Technical Specifications and Architecture
Under the hood, the 04 STI utilizes the EJ207 engine, a variant of Subaru’s renowned EJ series. This specific iteration features a forged crankshaft and pistons, allowing it to withstand the significant pressures of the turbocharged setup. The engine displaces 1,994cc and is mated to a robust 6-speed manual transmission, ensuring power is delivered efficiently to all four wheels through the symmetrical AWD system.
Forged Internals and Turbocharging
Key to the 04 STI’s performance is its forged bottom end, which provides the necessary strength for high-RPM operation and increased boost pressure. The turbocharger, often a Mitsubishi TD04-HR, spools quickly to deliver responsive power across the rev range. This combination results in a factory-rated output of 300 horsepower and 290 lb-ft of torque, figures that were competitive in the performance sedan segment at the time.
Driving Dynamics and Handling
Power is only half the equation; the chassis of the 04 STI is engineered to manage it. The model features enhanced suspension components, including a wider track and stiffer springs, compared to its WRX counterpart. This setup, combined with the center differential and active torque vectoring, provides exceptional grip and cornering stability, making the car feel planted and precise on both road and track.
Brakes and Cooling
To manage the energy of this dynamic machine, the 04 STI comes equipped with larger brake calipers and rotors than the standard WRX. This upgrade ensures confident and fade-resistant stopping power. Additionally, Subaru included an oil cooler and transmission cooler, which are critical for maintaining optimal performance and longevity during spirited driving or extended track sessions.
Legacy and Market Position
The 2004 model year holds a special place among enthusiasts, sitting at the sweet spot between earlier, more raw versions and later, more refined generations. It offered a balance of reliability, accessibility, and performance that solidified the STI nameplate. Today, well-maintained examples are highly sought after, often serving as a benchmark for used performance car buyers seeking value and driving engagement.
Maintenance and Considerations
Owning an 04 STI requires adherence to a strict maintenance schedule, particularly concerning the turbocharged engine and AWD system. Regular oil changes with high-quality synthetic oil are non-negotiable. Potential buyers should also be aware of the timing belt system and inspect components like the intercooler and turbo hoses for wear, as high mileage models may require attention in these areas.
