BC5901 – Polaris XP 1000 (2014-23) Stroker Crankshaft 78mm w/180° Crank Pin

For the dedicated Polaris XP 1000 builder seeking the definitive upgrade in rotational mass and power potential, the BC5901 78mm Stroker Crankshaft represents the pinnacle of performance engineering. This isn’t a mere replacement part; it’s a foundational component for a transformative engine build. Precision-machined from premium billet steel and featuring a 180° crank pin configuration, the BC5901 is engineered to increase displacement, optimize piston motion, and deliver a monumental gain in torque and horsepower. It is the critical upgrade for those who understand that true performance begins with the absolute integrity and specification of the rotating assembly. Designed specifically for the 2014-2023 Polaris ProStar 1000 engine, this crankshaft is the cornerstone for building a reliable, high-output machine capable of dominating dunes, trails, and track.

Engineering the Foundation: Billet Construction & 180° Crank Pin

At the core of the BC5901’s superiority is its material and manufacturing origin. Unlike forged or cast OEM-style crankshafts, this component is CNC-machined from a single, homogeneous block of SAE 4340 chromoly steel billet. This process ensures uninterrupted grain flow and eliminates the potential for internal flaws inherent in casting. The result is a crankshaft with exceptional tensile strength and fatigue resistance, capable of handling the immense stresses of increased displacement, forced induction, and high-RPM operation without flex or failure. The strategic use of cross-drilled and chamfered oil passages guarantees optimal lubrication to the rod journals, even under extreme load, significantly reducing wear and operating temperatures.

The defining feature of this stroker crank is its 180° crank pin configuration. This design places the connecting rods for cylinders 1 and 2 directly opposite each other on the crankpin, creating a perfectly balanced firing order (1-2). This layout yields several profound advantages. It produces a distinct, powerful exhaust note and, more critically, generates a broader, flatter torque curve compared to engines with split-pin cranks. The even firing intervals promote smoother power delivery and reduce harmonic vibrations, contributing to overall engine longevity. This design is favored for high-performance and racing applications where predictable, tractable power is paramount. For a deeper dive into crankshaft design principles, refer to this technical resource on crankshaft design and material science from Engine Builder Magazine.

Precision Performance Gains: The 78mm Stroke Advantage

The “78mm” specification is the key to unlocking substantial displacement gains. By increasing the stroke—the distance the piston travels within the cylinder—the BC5901 effectively increases the engine’s total swept volume. When paired with the appropriate cylinder bore, this stroker crank can elevate the ProStar 1000’s displacement to 1100cc or more, depending on the complete build package. This directly translates to a significant increase in torque, as a longer stroke inherently creates greater mechanical leverage. The engine will produce more power at lower RPMs, resulting in explosive throttle response, improved climb-out ability, and reduced need to constantly rev the engine to stay in the powerband. This low-end and mid-range grunt is transformative for technical riding, hill climbing, and towing.

Key Benefits of the BC5901 Stroker Crankshaft

• Massive Torque & Horsepower Increase: The 78mm stroke directly increases displacement, generating profound gains in low-end torque and overall horsepower.
• Superior Billet 4340 Steel Strength: CNC-machined from a single billet for maximum density, fatigue resistance, and ability to withstand boost and nitrous.
• Optimized 180° Crank Pin Design: Delivers a broad, flat torque curve, smooth power delivery, and a classic performance exhaust note.
• Precision Balanced & Blueprinted: Individually balanced to exacting tolerances for smooth operation at high RPM, reducing vibration and bearing wear.
• Enhanced Oil System: Cross-drilled and chamfered oiling passages ensure critical rod journals receive maximum lubrication under all conditions.
• Direct OEM Fitment: Designed to install into the ProStar 1000 engine cases using OEM bearings and seals without case modification.
• Foundation for Forced Induction: The overbuilt billet construction provides the necessary strength for reliable turbocharger or supercharger operation.

Technical Specifications & Build Requirements

Installing a stroker crankshaft is a system-level modification. The BC5901 requires complementary components to function correctly and safely. The increased stroke means standard pistons and connecting rods cannot be used. You must install a matched set of stroker-specific pistons (with a revised compression height and potentially different dome profile) and stroker-length connecting rods. Failure to do so will result in catastrophic piston-to-cylinder head contact. Additionally, engine tuning via a programmable ECU (such as those from Dynojet or EVO) is non-negotiable to properly manage air/fuel ratios and ignition timing for the new displacement and dynamic compression. The following table details the critical specifications of the BC5901 crankshaft.

Vehicle Fitment: 2014-2023 Polaris XP 1000

The BC5901 Stroker Crankshaft is engineered as a direct-fit performance upgrade for the following models. Ensure your machine’s model year and engine configuration match this list before purchase.

• Polaris RZR XP 1000 (All Models & Editions) – 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023
• Polaris RZR XP 4 1000 – 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023
• Polaris General XP 1000 – 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023
• Polaris Sportsman XP 1000 – All models utilizing the ProStar 1000 engine

Important Note: This crankshaft is designed for the twin-cylinder, 4-stroke ProStar 1000 engine. It is not compatible with the older 900 models or the newer ProStar 1000 High Output (HO) variants that use a different crank design. Always verify your engine’s internal configuration prior to disassembly.

Installation Overview & Final Build Considerations

Installation of the BC5901 crankshaft is a task for an experienced engine builder with the proper tools, including a case-splitting stand, hydraulic press, bearing installation tools, and a high-quality torque wrench. The process involves completely disassembling the engine, splitting the crankcases, removing the old crank, and pressing in the new crankshaft with the correct OEM-spec bearings. Critical attention must be paid to bearing alignment, seal installation, and final crank runout measurement. After assembly, the engine management system must be reprogrammed with a tune file calibrated for the new displacement, compression ratio, and any accompanying modifications (e.g., camshafts, intake, exhaust). Neglecting the tune will lead to pre-ignition, detonation, and rapid engine failure.

The BC5901 78mm Stroker Crankshaft is more than a part; it’s a commitment to building a superior engine. It provides the robust, precision-machined foundation upon which legendary power plants are constructed. By increasing displacement and optimizing the dynamics of the rotating assembly with its billet 4340 steel and 180° crank pin design, it unlocks the true performance potential trapped within the Polaris ProStar 1000 architecture. For the builder who accepts no compromises, the BC5901 is the essential first component in creating a torque-monster engine capable of dominating any terrain.