BC8860-EX: Brian Crower Adjustable Cam Gears for Subaru EJ Series (Exhaust Side Set)

Introduction: Mastering the Subaru EJ’s Final Breath

In the realm of forced induction performance, particularly within the legendary Subaru EJ engine series, volumetric efficiency is the ultimate currency. While much attention is rightly paid to turbo selection, intake manifolds, and fueling, the precise management of exhaust gas evacuation remains a critical, yet often under-optimized, frontier. The factory cam gears on your EJ205, EJ207, EJ255, or EJ257 are fixed, locking you into a compromise-based timing setting that caters to emissions, fuel economy, and broad manufacturing tolerances—not peak power or bespoke tuning. The Brian Crower BC8860-EX Adjustable Cam Gears exist to shatter that compromise. This exhaust-side-specific set is not a mere accessory; it is a fundamental tuning tool engineered for the mechanic and builder who demands absolute authority over the engine’s exhaust valve timing. Manufactured from 6061-T6 billet aluminum and featuring a meticulous +/- 10 degrees of adjustability, these gears provide the pivotal control needed to dial in spool characteristics, maximize top-end flow, and fine-tune the power band to complement aggressive camshaft profiles and large turbochargers. This is about transforming exhaust pulses from mere waste expulsion into a tuned, scavenging force that actively contributes to power production.

Core Function & Engineering Philosophy

The primary function of the BC8860-EX adjustable cam gear is to allow independent alteration of the exhaust camshaft’s timing relative to the crankshaft. In a boxer engine like the Subaru EJ, where packaging is tight and thermal management is crucial, the exhaust side bears the brunt of heat and stress. Advancing or retarding the exhaust cam timing directly influences when the exhaust valves open and close in relation to the piston’s position in the cylinder.

Advancing the Exhaust Timing (opening the valve earlier) helps in high-RPM, high-boost scenarios by initiating the exhaust process sooner, reducing pumping losses and combating residual cylinder pressure that can impede piston ascent. This can enhance top-end horsepower but may sacrifice some low-end torque and spool response.

Retarding the Exhaust Timing (keeping the valve open later) can improve low-end and mid-range torque by allowing more complete combustion before evacuation begins, which is beneficial for street-driven cars or setups targeting a fat, responsive power curve. The ability to fine-tune this parameter, often in conjunction with adjustable intake gears, is what separates a generic build from a professionally optimized one. Brian Crower’s design focuses on providing this control with zero compromise on strength or precision, recognizing that the exhaust side’s environment demands the utmost durability.

Technical Specifications & Construction Analysis

Every dimension and material choice in the BC8860-EX is a calculated decision for performance and reliability under duress.

The use of 6061-T6 billet aluminum is non-negotiable. Unlike cast or powdered metal OEM gears, billet aluminum has a continuous grain structure, eliminating potential weak points and porosity. This provides exceptional strength-to-weight ratio and resistance to fatigue from the constant harmonic forces and heat cycles of the exhaust side. The laser-etched markings ensure precise, repeatable adjustments that will not wear off, while the OEM-spec tooth profile guarantees seamless integration with your existing timing belt system without risk of jump or accelerated wear. For a deeper technical understanding of cam timing effects on turbocharged engines, reputable sources like Engine Basics provide excellent foundational knowledge.

Performance Benefits & Tuning Advantages

Installing the BC8860-EX adjustable cam gears unlocks a suite of tuning capabilities that directly translate to measurable performance gains and improved engine behavior.

• Optimize Turbocharger Spool: By fine-tuning exhaust valve overlap and opening events, you can tailor exhaust pulse energy to more efficiently drive the turbocharger’s turbine, reducing lag and improving transient response.
• Correct for Aftermarket Camshafts: Aggressive cam profiles often require timing adjustments to realize their full potential. These gears allow you to dial in the exact centerline recommended by your cam manufacturer or discovered through dyno tuning.
• Maximize High-RPM Volumetric Efficiency: Properly set exhaust timing enhances cylinder scavenging at high engine speeds, clearing spent gases more effectively to make room for a larger, cooler intake charge.
• Fine-Tune the Power Band: Shift the torque curve to better suit your application—whether it’s early torque for a daily driver or a top-end focus for track use.
• Compensate for Engine Build Tolerances: Account for deviations caused by decking the block, milling heads, or using multi-layer head gaskets, ensuring your timing belt alignment and valve events are precisely where they need to be.
• Durability & Reliability: The billet construction is far more resistant to wear, tooth deformation, and failure under high-load conditions compared to stock gears, a critical upgrade for high-horsepower builds.

Vehicle Fitment & Application Notes

Vehicle Fitment: The BC8860-EX is engineered specifically for the exhaust camshafts of Subaru’s EJ series turbocharged engines. Confirmed fitment includes, but is not limited to, the following popular applications:

• Subaru Impreza WRX (2002-2007) with EJ205/EJ255 engines
• Subaru Impreza WRX STI (2004-2007) with EJ257 engine
• Subaru Impreza WRX STI (JDM versions) with EJ207 engine
• Subaru Forester XT (2004-2008) with EJ255 engine
• Subaru Legacy GT (2005-2009) with EJ255 engine
• Other turbocharged EJ-series variants (EJ255, EJ257, EJ207, EJ205)

Critical Application Note: This is a set of two gears for the exhaust side only. For full variable valve timing control, these are typically paired with the intake-side counterpart (e.g., BC8860-IN). Installation requires partial engine disassembly to access the timing belt area. Proper locking of the camshafts with tools is mandatory to prevent engine damage during gear swap and timing belt re-installation. Final timing adjustments should be made with the engine at Top Dead Center (TDC) and confirmed with a degree wheel and dial indicator for professional-grade accuracy. Always use a new timing belt and idlers when performing this installation.

Installation Considerations & Final Tuning

Installing adjustable cam gears is a precision task. After physically installing the BC8860-EX gears and setting them to a “zero” baseline (aligned with OEM timing marks), the real work begins. Tuning requires a chassis dyno with load control and an experienced tuner who can interpret data logs. The process involves making incremental adjustments (typically starting with 2-degree changes), logging the effects on torque, horsepower, boost response, and often exhaust gas temperatures (EGT). The goal is to find the sweet spot where your specific combination of turbo, cam, intake, and exhaust produces the desired power curve. Remember, changes to exhaust timing can affect ignition timing requirements and fuel maps, necessitating a comprehensive retune. These gears are the final, critical step in synchronizing all the high-performance components of your EJ build into a harmonious, powerful, and reliable whole.