YZ250 2T 300 cc Big Bore Cylinder Kit Ø 72 mm, 293 cc and Exhaust Valve Kit NEW VERSION

The Yamaha YZ250 has long been recognized as one of the most competitive and versatile two-stroke motocross bikes. For riders looking to unlock additional performance and tailor engine character to specific track conditions, Athena has developed the new Big Bore 300cc Cylinder Kit, engineered to increase displacement, improve power output, and deliver a more responsive riding experience.

Engineered for Higher Performance

This latest-generation Big Bore Cylinder Kit represents a major evolution over the previous version. Every component has been redesigned and optimized to improve power, reliability, and overall rideability, making it suitable for both competitive racing and serious off-road use.

Redesigned Cylinder for Maximum Output

The aluminum cylinder features a completely revised port layout developed to optimize gas flow and combustion efficiency. The updated internal geometry delivers stronger mid-range and top-end performance while maintaining excellent low-rpm response.

High-Efficiency Cylinder Head Design

The newly developed cylinder head has been engineered to optimize compression ratio and combustion chamber efficiency. The result is improved throttle response, enhanced combustion quality, and more precise power delivery throughout the rpm range.

Adjustable Squish and Power Delivery Configurations

Engine behavior can be customized by adjusting squish clearance and the resulting cylinder height. To provide multiple setup options, the kit includes different cylinder base gaskets that allow riders to fine-tune engine characteristics according to riding style and track conditions.

HARD Configuration
An extremely aggressive and explosive power delivery designed for sand tracks, supercross, and situations requiring maximum acceleration.

MEDIUM Configuration
A more progressive low-rpm power delivery with virtually no reduction in peak power, providing an excellent balance between performance and rideability.

SOFT Configuration
A smoother and more controllable power delivery at low and mid rpm, improving traction and rider confidence on technical terrain.

High-Performance Cast Piston

The newly developed cast piston reduces reciprocating mass and improves engine responsiveness. Lower inertia contributes to quicker acceleration and enhanced overall engine efficiency.

Optimized Exhaust Valve System

The redesigned exhaust valve components work in conjunction with the new cylinder port timing to improve high-rpm breathing while maintaining strong low-end torque and rideability.

Complete Kit for Professional-Level Performance

Like all Athena cylinder kits, this package includes premium-quality gaskets and components designed to ensure durability, reliability, and consistent performance under the most demanding racing conditions.

• Athena PN
• P400485100104