BC8860B-EX – Subaru EJ Series Adjustable Cam Gears – Exhaust Side Only – All Black (set/2)

Introduction: Mastering Exhaust Valve Events with Precision-Adjusted Timing

For the dedicated Subaru EJ series tuner and builder, achieving optimal engine performance is a symphony of precise air management. While intake modifications often steal the spotlight, the exhaust cycle is where significant power is left on the table without proper control. The Brian Crower BC8860B-EX Adjustable Cam Gears are engineered to reclaim that power. This exhaust-side-only set represents a critical tool for advanced engine calibration, offering machinists and performance enthusiasts unparalleled command over exhaust valve timing. Designed specifically for the rugged demands of the EJ platform—from the venerable EJ205 to the dominant EJ257—these all-black adjustable cam gears provide the fine-tuning capability necessary to maximize turbo spool, improve top-end power, and correct for valvetrain geometry changes after significant head or block machining. This is not a generic modification; it is a fundamental calibration component for any serious build targeting efficiency, response, and ultimate power output.

Engineering and Design: The Anatomy of Precision Adjustment

The BC8860B-EX cam gears are a product of rigorous CNC machining from high-grade 6061-T6 billet aluminum, chosen for its exceptional strength-to-weight ratio and resistance to harmonic distortion. The all-black anodized finish is not merely aesthetic; it provides a durable, corrosion-resistant surface that withstands the heat and contaminants of the engine bay. The core innovation lies in the adjustable timing mechanism. Each gear features a series of precision-machined slots and locking points, allowing for camshaft timing adjustment in precise, typically one-degree increments. This system securely locks the cam sprocket to the camshaft via high-tensile alloy steel hardware, preventing any slippage under high-RPM load—a critical failure point in inferior designs. The gear’s tooth profile is an exact OEM match, ensuring perfect meshing with the timing belt and eliminating the risk of premature belt wear or jumping time, a non-negotiable safety feature for an interference engine like the Subaru EJ.

Performance Benefits and Tuning Applications

Installing adjustable exhaust cam gears unlocks a new dimension of tunability. The primary function is to alter the exhaust valve opening (EVO) and closing (EVC) events independently of the intake cam. This allows tuners to tailor the engine’s characteristics to specific goals.

• Optimize Turbocharger Spool: Advancing exhaust cam timing can lower the effective turbocharger threshold RPM, reducing lag and improving low-end and mid-range torque response by harnessing exhaust gas energy more effectively.
• Increase High-RPM Power: Retarding exhaust cam timing can help scavenge cylinders at higher engine speeds, supporting greater volumetric efficiency and pushing the power band further into the RPM range.
• Correct Cam Timing After Machining: Following head resurfacing or block decking, the relationship between the crankshaft and camshafts changes. These adjustable gears allow you to dial the exhaust cam timing back to its optimal factory specification or beyond.
• Balance Cylinder-to-Cylinder Exhaust Flow: Minor manufacturing variances can be compensated for, promoting more even exhaust gas temperatures (EGT) across all cylinders, which is crucial for engine longevity and consistent power delivery.
• Fine-Tune Overlap with Fixed Intake Cams: For builds using adjustable exhaust gears with stock or non-adjustable intake gears, you can still modify the valve overlap period to influence idle quality, emissions, and power curve shape.

As discussed in technical resources on forced induction tuning, such as this detailed analysis of cam timing in forced induction engines, the exhaust side plays a disproportionately large role in managing backpressure and scavenging efficiency in turbocharged applications.

Vehicle Fitment and Compatibility

The BC8860B-EX is engineered as a direct replacement for the OEM exhaust cam gears on a wide range of Subaru EJ series engines. Correct fitment is paramount to ensure proper timing belt alignment and valvetrain operation. This set is specifically designed for the exhaust camshafts only and is sold as a pair for a complete exhaust side upgrade.

Primary Applications Include:
Subaru WRX (2002-2014) with EJ205 & EJ255 engines
Subaru STI (2004-2021) with EJ255 & EJ257 engines
Subaru Forester XT (2004-2018) with EJ255 & EJ257 engines
Subaru Legacy GT & Outback XT (2005-2012) with EJ255 engines
Compatible with most naturally aspirated EJ25x variants where adjustable timing is desired (verification of cam sensor trigger style recommended)

Important Note: These gears are intended for use on engines with non-AVCS (Active Valve Control System) camshafts or on the exhaust side of engines where the AVCS system is retained only on the intake side. For dual-AVCS engines, specialized gears are required. Always verify your engine’s specific camshaft and sensor configuration before purchase.

Technical Specifications and Installation Data

Installation requires a comprehensive timing belt service procedure. The engine must be set to top dead center (TDC) on cylinder #1, and the OEM timing marks must be meticulously referenced. After installing the adjustable gears in their “zero” position, final timing adjustments should be made using a dial indicator and degree wheel to measure actual camshaft lobe position, not merely relying on gear markings. This ensures absolute accuracy. Always torque the mounting hardware to the manufacturer’s specified value, typically between 70-85 ft-lbs, and use a quality thread-locking compound as specified.

Conclusion: The Essential Tool for Exhaust Tuning Precision

The Brian Crower BC8860B-EX Adjustable Cam Gears transcend the category of a simple bolt-on part. They are a calibration instrument, integral to unlocking the full potential of a modified Subaru EJ engine. By providing exacting control over exhaust valve timing, they address the specific bottlenecks of turbocharged performance—lag, scavenging, and thermal management. For the builder performing head work, they are indispensable for restoring proper engine geometry. Their robust construction guarantees reliability under the extreme conditions of high-horsepower and high-RPM operation. If your build strategy involves a performance camshaft, increased boost, or meticulous efficiency tuning, these adjustable exhaust gears are not an option; they are a foundational component for a complete, balanced, and powerful engine system. Invest in the precision that delivers definitive results.