Big Bore Complete Kit (900cc) / Patriot 850

SKU: 09-311-com-1
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$4,095.95 USD
CHOOSE ELEVATION FOR BILLET HEAD DOMES
CHOOSE SLED FOR CLUTCH KIT
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CYLINDER CORE EXCHANGE NOTICE: This kit requires modifying your factory cylinder and exhaust valve blades. Turnaround time is typically 3-5 business days (up to 15 days in peak season if cores are out of stock). Please read the Core Exchange Options below carefully before ordering.

900cc Big Bore Complete Performance Kit for Polaris Patriot 850 (Long Track / Mountain) // SKU: 13-310-900-M

Primary Application: Polaris RMK, PRO-RMK, Khaos, SKS, and Switchback Assault models equipped with 2.0" or deeper lug tracks.

The Polaris Patriot 850's massive 74mm stroke was practically begging for a bigger bore, and we’ve done the homework to bring you the ultimate 900cc Big Bore Complete Kit. By boring your factory cylinder to accept ultra-high-quality, dual-ring 88mm Factory Polaris 9R Forged Pistons, this kit transforms your 850 into a 195+ horsepower mountain-conquering monster.

If you are a technical tree rider or steep-incline climber who demands zero-lag power the absolute instant you hit the throttle, this is your kit. Paired with our Bikeman exclusive Billet Head profile, full Fatt Azz exhaust system, and Stage 2 mountain clutching, this 900cc setup delivers endless mid-range torque and explosive track speed to get you out of the hairiest riding situations.

1. Cylinder Core Exchange Options (Select on Page)

Because this kit uses modified factory Polaris cylinders and exhaust valves, you must select one of the following fulfillment methods:

  • Option 1: Purchase Outright (+$1,600): No core cylinder or exhaust valve blades are required to be sent in. We ship you a completed 900cc kit. (Raises kit price by $1,600).

  • Option 2: Core Charge / Refund: Pay the upfront $1,600 core charge, and we ship your kit immediately (if in stock). You MUST send us your pristine factory cylinder and exhaust valve blades within 14 business days of receipt. Once inspected and approved, the $1,600 charge will be refunded. Cores received after 14 days will receive NO credit and you will be responsible for return shipping.

  • Option 3: Send In Advance (No Core Charge): Your order is placed on hold. Remove your factory cylinder and exhaust valve blades and mail them to us. Once they arrive, we bore/port your cylinder and ship the completed kit back to you (normally within a few business days). No $1,600 core charge is ever applied.

2. Digital Tuning Platform

This massive displacement increase requires entirely new fueling and timing parameters. A bench ECU Hard Flash is included standard, or you can upgrade to mobile tuning:

  • Standard: ECU Hard Flash (Send-In Bench Service): Remove your ECU and mail it directly to our facility with your cylinders. We flash our custom 900cc tune file and ship it back ready to plug in and ride.

  • Optional Upgrade: Torque Link Pro (Mobile Tuning): Flash your ECU directly from your smartphone via Bluetooth/Wi-Fi. Grants full access to tune libraries and real-time diagnostic engine logging trailside.

3. Performance Bolt-On Hard Parts Included

  • 900cc Big Bore Engine Kit: Your factory cylinder and exhaust valve blades meticulously CNC-bored and ported to 900cc spec.

  • Factory 9R Polaris Pistons: Premium 88mm dual-ring forged pistons direct from the Polaris 9R parts bin for unmatched durability and sealing.

  • Billet Cylinder Head Kit (SKU: 04-318): CNC-machined 6061 billet head shell. (Select Low Altitude 0-6k ft, or High Altitude 6k+ ft domes from the dropdown menu to maintain optimal compression and knock protection).

  • Fatt Azz Single Expansion Pipe (SKU: 01-328): Ceramic-coated (1,300°F) expansion chamber included with our Fast Reaction 9R Internal Stinger (01-328-9R) to perfectly match the 900cc exhaust gas volume and backpressure needs.

  • Ceramic Performance Exhaust Manifold (Y-Pipe) (SKU: 03-302-C): High-flow manifold to eliminate internal exhaust turbulence.

  • Complete Stage 2 SNYPR Mountain Clutch Kit: Fully adjustable primary weights, primary/secondary springs, custom mountain helix, and the heat-slashing Billet Cyclone Primary Clutch Cover.

Vehicle Fitment & Lug Depth Rules

  • Compatible Sled Models: Fits all Polaris RMK, PRO-RMK, Khaos, SKS 146 / 155, and Switchback Assault models equipped with 2.0" or deeper lug tracks across all chassis platforms (AXYS & Matryx, 2019+).

  • TRACK LUG CUTOFF RULE: ANY Polaris Patriot 850 running a 2.0" or deeper lug track MUST use this mountain kit configuration.

  • CRITICAL CHASSIS EXCLUSION: Does NOT fit Hill Climb Racer (RMSHA / HCR) competition chassis models due to modified shock tower clearances.