BC5910 – Unbalanced Polaris XP Turbo (16-up) Stock Stroke Crankshaft 68mm w/270° Crank Pin

In the relentless pursuit of horsepower and durability for the Polaris XP Turbo platform, the foundation of your engine’s rotating assembly is non-negotiable. The stock crankshaft, while adequate for OEM applications, often becomes the critical failure point under increased boost and RPM. Enter the BC5910 from Brian Crower—a purpose-built, unbalanced stock stroke crankshaft engineered not as a mere replacement, but as a fundamental upgrade for the serious builder. Designed specifically for the 2016-and-newer Polaris XP Turbo, this 68mm stroke, 270° crank pin component is the bedrock for high-horsepower, high-reliability builds. It transforms the ProStar 1000 engine from a potential liability into a forged rotating asset, capable of withstanding the brutal forces generated by aggressive tuning, upgraded turbos, and sustained high-load operation. This is not a part for the casual rider; it is a precision instrument for those who understand that true performance starts from the center out.

Engineering Philosophy: The Unbalanced Advantage

To the uninitiated, the term “unbalanced” may raise concerns. In high-performance crankshaft engineering, however, it signifies intent and capability. The BC5910 is supplied unbalanced because true performance engines are balanced as a complete rotating assembly—crankshaft, rods, pistons, and even the clutch. This allows your engine builder to achieve a perfect, tailored balance specific to your component weights and intended RPM range, eliminating harmonic vibrations that destroy bearings and lead to catastrophic failure. Brian Crower’s pedigree in professional motorsport is evident in the BC5910’s construction. It is a fully forged 4340 chromoly steel assembly, a material whose superior tensile strength and fatigue resistance far surpass the OEM’s cast and powdered metal construction. The forging process aligns the metal’s grain structure, creating a part that is inherently stronger and more resistant to the twisting and bending forces (torsional and axial loads) endemic to high-output turbocharged engines.

The 270° Crank Pin: A Symphony of Pulse and Power

The heart of the BC5910’s character lies in its 270° crank pin configuration. Unlike a traditional 180° crank that fires cylinders in evenly spaced intervals, the 270° design creates an uneven firing order. This results in a distinct, lumpy exhaust note and, more importantly, a specific power delivery profile. The primary mechanical benefit is a reduction in inertial mass overlap at Top Dead Center (TDC), which can decrease parasitic losses and improve throttle response. The firing sequence promotes stronger scavenging pulses in the exhaust, which, when paired with a properly tuned system, can enhance turbo spool characteristics and broaden the powerband. This design is a calculated choice for performance, offering a tangible difference in engine feel and efficiency over the stock 180° layout.

Definitive Benefits of the BC5910 Crankshaft

• Forged 4340 Chromoly Steel Construction: Provides ultimate strength and fatigue resistance for high-boost and high-RPM applications, far exceeding OEM durability.
• Supplied Unbalanced for Precision Assembly: Enables perfect engine-specific balancing with your chosen rods and pistons, eliminating destructive harmonics for maximum longevity.
• 270° Crank Pin Design: Offers a unique firing order for improved exhaust scavenging, potential gains in throttle response, and a distinctive power delivery character.
• 68mm Stock Stroke: Maintains factory displacement and compatibility while providing a massively strengthened foundation for your build, ensuring proper fitment with OEM and aftermarket cylinders.
• Direct Replacement for OEM (P/N 4012941): Engineered for seamless installation into the XP Turbo crankcase without modification, a true bolt-in core upgrade.
• Enhanced Bearing Surfaces: Precision machining and superior material quality provide a more stable and durable surface for the main and rod bearings, crucial for oil film integrity.
• Blueprint for Forced Induction: Designed from the outset to handle the increased cylinder pressures and dynamic loads generated by turbocharging, making it the mandatory first step for any significant power increase.

Vehicle Fitment & Application Notes

Primary Application: This crankshaft is designed exclusively for the liquid-cooled, twin-cylinder Polaris ProStar 1000 (1000cc) engine found in the XP Turbo platform.

Specific Model Fitment (2016 and Newer):

• Polaris RZR XP Turbo (All Variants: Base, Dynamix, Premium)
• Polaris RZR XP Turbo S (2017-2018, prior to the switch to the 72″ Turbo S model)
• Polaris General XP Turbo
• Polaris RZR Pro XP (Note: The 2019+ Pro XP utilizes a different engine architecture and is NOT compatible)

Critical Installation Consideration: The BC5910 is an unbalanced crankshaft. Successful installation requires that the entire rotating assembly (crankshaft, connecting rods, pistons, pins, and rings) be professionally balanced as a unit by a qualified engine machinist. Pairing this crank with unbalanced components will lead to severe vibration and rapid engine failure. It is highly recommended to use it in conjunction with forged connecting rods and pistons from a quality manufacturer like Brian Crower or CP-Carrillo to create a cohesive, bulletproof rotating assembly. For a deeper technical understanding of crankshaft balancing and its effects on engine longevity, refer to this authoritative resource on engine balancing principles at Engine Builder Magazine.

Technical Specifications

Installation & Break-In Protocol

Installing the BC5910 is a task for a professional engine builder with experience in performance UTV assemblies. After the mandatory balancing process, cleanliness and precise bearing clearance measurements are paramount. Use a high-quality assembly lubricant and follow the recommended main and rod bearing clearance specifications for your application, typically between 0.002″ – 0.0025″. Upon initial startup, adhere to a strict break-in procedure using non-synthetic oil: run the engine at varying RPMs (avoiding sustained idle or high load) for approximately 30 minutes to properly seat the bearings and establish a wear pattern. After this initial cycle, change the oil and filter to remove any assembly debris and initial wear particles. This crankshaft is built for endurance, but its longevity is directly proportional to the care taken during installation and the quality of the supporting components in your build.