Brand New Subaru WRX STI B25 Cylinder Head Premium Aftermarket Loaded (Left)

Subaru WRX STI B25 Left Side Cylinder Head – Loaded & Brand New

Fully Assembled Performance Head for EJ255/EJ257 Turbocharged Engines

Restore your Subaru’s legendary boxer performance with this premium, brand-new B25 Left-Side (LH) cylinder head. Specifically engineered for the high-output 2.5L Turbocharged DOHC (EJ255/EJ257) engine series, this aftermarket casting is designed to optimize volumetric efficiency and withstand the extreme thermal stresses inherent to forced induction. Unlike standard bare castings, this unit arrives as a “drop-in” ready solution, fully loaded with a complete valvetrain to minimize installation downtime.

Utilizing a high-density aluminum alloy with reinforced coolant jackets, this B25 head is precision-machined to meet or exceed original equipment (OE) dimensional tolerances. This ensures an absolute deck surface finish for a superior head gasket seal—critical for preventing the common failures found in high-boost EJ-series engines. Every unit features precision-seated valves, calibrated springs, camshafts, lifters, and rockers, all pre-assembled and inspected for proper lash and alignment. Whether you are performing a top-end rebuild on an Impreza WRX STI, Forester XT, or Legacy GT, this B25 casting provides the structural integrity and cooling capacity required to sustain factory boost levels and regain peak horsepower.

🛠️ In-House Machining Process

• Debris-Free Preparation: Every new casting is chemically cleaned and blown out to remove all residual machining oils, metal shavings, and manufacturing debris. This ensures your oiling system remains uncontaminated from the first start-up.

• In-House Precision Machining: Unlike “shelf-stock” heads, we perform all final machine work in-house. This includes final guide sizing and precision valve seat cutting to ensure perfect geometry and clearances before the head reaches the assembly bench.

• Pressure & Integrity Testing: To go beyond the factory standard, we pressure-test every head to 60 PSI. This verifies that the casting is free of porosity leaks or internal defects that could compromise the cooling or oiling systems.

• Dimensional Inspection: Our technicians perform a multi-point inspection of the gasket-sealing surface and bore alignment. This ensures the head is perfectly flat and meets tight OEM tolerances for a flawless fit.

• Professional Assembly & Setup: Valvetrain components are installed and verified in a clean-room environment. We check spring heights and seal seating to ensure the assembly is balanced and ready for high-performance use.

• Vacuum-Seal Verification: Every intake and exhaust port is Vacuum Tested. This guarantees a 100% airtight seal between the valves and seats, ensuring maximum compression and peak performance right out of the box.

🛠️ Premium Build & Valvetrain

• Brand New Casting: High-quality alloy construction for maximum heat dissipation and durability.
• Fully Loaded Assembly: Pre-installed with valves, springs, and camshafts.
• Turbo-Optimized: Engineered specifically for the B25 casting requirements found in early STI and XT models.
• Plug-and-Play: Ready to bolt on straight out of the box—no need to swap over high-mileage internal components.

📊 Technical Specifications

• Engine Type: Subaru 2.5L DOHC Turbocharged (EJ25)
• Casting Designation: B25 (Left Side)
• Condition: Brand New Aftermarket
• Each Cylinder Head Includes: Valves and Springs Installed, Camshafts Installed, Bucket Lifters Installed and Lash Set 

🚛 Fitment Data

Common Applications (2.5L Turbo):

• Subaru Impreza WRX STI: 2004–2005 (2.5L Turbo)
• Subaru Forester XT: 2004–2005 (2.5L Turbo)
• Subaru Baja Turbo: 2004–2005 (2.5L Turbo)
• Subaru Legacy GT: 2005–2006 (2.5L Turbo)

Important: This is the LEFT SIDE cylinder head only. Please verify your vehicle matches the fitment details and casting requirements before purchasing.