CYLINDER KIT 85mm YAMAHA YZ 250F 25-26 ATHENA P400485100112 BIG BORE 304CC
Big bore cylinder kit for the Yamaha YZ-F 250 cc from 2025 to 2026, designed to increase engine displacement to 304.15 cc and provide increased torque and power throughout the RPM range while retaining the motorcycle’s agility and responsiveness. The kit combines an oversized cylinder and forged piston assembly with the pre-calibrated GET Boost electronic module, providing the components required for the increased-capacity engine configuration.
Features
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High-grade cylinder with oversized steel liner
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Forged performance piston supplied with pin and rings
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Includes all necessary gaskets
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GET Boost electronic module included
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GET Boost is pre-calibrated specifically for the big bore configuration
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Installs without ECU or wiring modifications
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Dedicated harness connects directly to the injector and throttle body
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Pre-mapped power curve for safe and reliable operation with the new cylinder
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Developed using experience from MXGP and AMA racing
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Designed for smooth, progressive power delivery across the RPM range
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MLS head gasket provides combustion sealing and long-term durability
Specifications
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Bore diameter: 85.00 mm
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Bore gain: +8 mm
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Compression ratio: 13.3:1
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Displacement: 304.15 cc
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Cylinder material: high-silicon aluminium alloy
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Cylinder liner: steel
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Liner construction: proprietary co-casting process
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Piston: forged and CNC-machined
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Piston coating: molybdenum disulphide
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Piston pin coating: DLC
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Head gasket type: MLS (Multi-Layer Steel)
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Head gasket material: laser-cut stainless steel
Cross-Reference OEM Part Numbers
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Athena: P400485100112
Vehicle Fitments
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Yamaha YZ-F 250 cc: 2025–2026