Brand New Subaru Wrx Sti B25 Cylinder Heads Premium Aftermarket Bare Castings (Left Side)

Subaru WRX STI B25 Left Side Cylinder Head – Brand New Bare Casting

Driver’s Side Replacement for 2.5L DOHC Turbocharged Engines

Upgrade your Subaru’s EJ-series boxer engine with this premium, brand-new B25 Left-Side (LH) driver-side bare cylinder head. Specifically engineered for 2004–2006 turbocharged EJ255 and EJ257 platforms, this aftermarket casting is designed to address the thermal and structural demands of forced induction. Unlike standard factory replacements, this “reinvigorated” B25 casting features reinforced wall thickness in critical high-stress areas, providing a significant increase in durability and resistance to the deck warping common in high-boost applications.

As a bare casting, this unit offers professional engine builders and Subaru enthusiasts the ultimate technical flexibility. It serves as a “zero-hour” foundation, allowing for the custom installation of performance valves, high-rate springs, and aggressive camshaft profiles tailored to specific power goals. Every B25 head undergoes precision CNC machining to meet or exceed original equipment (OE) dimensional tolerances, ensuring absolute deck flatness for a superior multi-layer steel (MLS) head gasket seal. Whether you are performing a factory-spec restoration or a high-horsepower build for an STI, Forester XT, or Legacy GT, this reinforced B25 head provides the structural integrity and cooling capacity required for long-term reliability.

🛠️ 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.

🛠️ Engineering & Performance Features

• Enhanced Strength: Manufactured from high-strength alloys with increased wall thickness to prevent common cracking issues.
• Driver’s Side Fitment: Specifically machined for the left side (Bank 2) of the Subaru 2.5L flat-four engine.
• Customizable Bare Casting: Delivered without internals, allowing you to select your own valves, springs, and camshafts.
• Rigorous Quality Control: Every head is thoroughly cleaned, vacuum tested, and pressure tested to exceed OEM performance standards.

📊 Technical Specifications

• Engine Type: Subaru 2.5L DOHC Turbocharged (EJ25)
• Casting Designation: B25 (Left/Driver Side)
• Condition: Brand New Aftermarket
• Format: Bare Casting (Components not included)

🚛 Fitment Data

Compatible with 2.5L DOHC Turbocharged Models:

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

Important fitment note: This listing is for the LEFT (Driver’s) side only. Please ensure your vehicle uses the B25 casting before ordering.