BC3105 – Mitsubishi 4G63/Evo Exhaust Valves (31.5mm / +1mm) – set/8

In the realm of high-output Mitsubishi 4G63 engines, from the venerable DSM platforms to the legendary Evolution series, the exhaust valve is a critical point of failure under sustained thermal and mechanical load. The BC3105 Exhaust Valve Set from Brian Crower is engineered not as an incremental upgrade, but as a foundational component for built motors targeting reliable horsepower. Specified at a 31.5mm head diameter—a purposeful +1mm oversize from stock—this set of eight valves is designed to facilitate improved exhaust flow for turbocharged applications, while its material science and manufacturing precision address the specific weaknesses that lead to valve float, tulip fatigue, and stem galling in competition environments. This is a component for builders who understand that peak cylinder pressure management begins with unimpeded exhaust evacuation.

Core Technology & Design Philosophy

Brian Crower’s BC3105 valves are a product of targeted engineering, where every dimension and material property is optimized for the 4G63’s combustion dynamics. The +1mm oversize is a calculated increase, maximizing port and chamber real estate without necessitating radical, costly machining that compromises chamber integrity or quench areas.

Precision Oversizing for Flow & Durability

The 31.5mm head diameter provides a significant increase in flow potential, particularly beneficial in turbocharged applications where reducing backpressure post-turbine is paramount. The backside of the valve head is machined with a specific profile to maintain a strong, lightweight structure that resists deformation under extreme heat. Crucially, the transition from stem to head (the fillet radius) is meticulously contoured to reduce stress concentration, a common failure point in inferior valves subjected to high RPM valve train shock.

Performance Benefits & Application Scope

Integrating the BC3105 valve set transforms the exhaust side of your valvetrain from a potential liability into a asset of durability and performance. These benefits are realized across the power band, from improved spool characteristics to unwavering top-end stability.

• Enhanced Exhaust Flow: The +1mm oversize directly increases flow capacity, reducing pumping losses and allowing for more aggressive cam timing and boost profiles.
• Superior High-Temperature Strength: Manufactured from high-grade EV8+ alloy steel, these valves maintain tensile strength and resist creep at sustained EGTs exceeding 1600°F.
• Reduced Valve Train Mass: Precision machining minimizes weight without sacrificing strength, allowing for higher stable RPM limits and reduced stress on springs and retainers.
• Optimized Wear Characteristics: The chrome-plated stems and hardened tips dramatically reduce guide wear and prevent tip mushrooming, ensuring consistent valve lash over long intervals.
• Direct, No-Compromise Fitment: Designed as a drop-in upgrade for stock or lightly machined heads, they interface perfectly with OEM or performance valve guides and seals.

Material & Construction Analysis

The specification sheet only tells part of the story. The true merit of the BC3105 lies in its material pedigree and finish quality, processes that separate a durable component from a disposable one.

EV8+ Alloy Steel & Critical Surface Treatments

The valve blanks are forged from EV8+ alloy steel, a material chosen for its excellent balance of fatigue resistance, hardness, and thermal conductivity. This base material is then subjected to a multi-stage thermal cycling process to achieve a uniform grain structure. The stems receive a thick, industrial-hard chrome plating. This isn’t a cosmetic layer; it’s a functional barrier that reduces friction coefficient against valve guides, resists micro-welding (galling), and provides exceptional corrosion resistance. The tips are induction hardened to a Rockwell specification that prevents peening and deformation from repeated hammering by rocker arms or lifters, a critical detail for engines using aggressive ramp rate camshafts.

Vehicle Fitment & Installation Notes

The BC3105 is engineered for a specific family of engines. Correct installation is paramount to realizing its performance and durability benefits. Valve seat machining must be performed by a machinist familiar with performance clearances and multi-angle seat jobs.

Primary Fitment: Mitsubishi 4G63 2.0L DOHC Turbo engines (1990-2006). This includes:

• Mitsubishi Eclipse GS-T, GSX (1990-1999)

• Eagle Talon TSi, Plymouth Laser RS Turbo (1990-1994)

• Mitsubishi Evolution III, IV, V, VI, VII, VIII, IX (1995-2006)

• Various JDM 4G63T applications from Galant VR-4, RVR Hyper Sports Gear, etc.

Installation Requirements: Installation requires machining of the cylinder head exhaust valve seats to match the new 31.5mm diameter and the specified seat angle (typically 45°). A precise valve job is non-negotiable for proper sealing and heat transfer. Always check and adjust valve-to-piston clearance, especially when pairing with high-lift camshafts or altered deck heights. Use quality valve stem seals and verify stem-to-guide clearance is within specification (typically 0.001″ to 0.003″).

Technical Specifications

For the builder focused on creating a resilient, high-flowing 4G63 platform—whether for time-attack, drag racing, or a high-boost street build—the Brian Crower BC3105 valve set provides the material integrity and dimensional precision required. It is a component that operates silently within the chaos of combustion, its value measured in consistent power cycles and the absence of failure.