To handle the internal pressures of a four-stroke engine, Vertex's big bore four-stroke pistons are forged from the highest quality 2618 aluminum alloy for superior strength and durability. Vertex uses unique piston profiles and compression ratios to maximize power and performance while reducing blow-by and oil consumption. Each Vertex piston is then hand matched to fit each Cylinder Works cylinder perfectly. Replacement standard piston for the Cylinder Works Big Bore Kit. All pistons include rings, pin, and clips. Detailed Specifications: Big Bore Piston kit: +3 mm makes 478cc. Compression ratio (x:y): 0.50069444. Cylinder diameter (mm): 98.00. Displacement (cc): 478.00. Piston diameter (mm): 97.96. SizeOverStandard (mm): 3. Note: For Cylinder Works cylinder kits ONLY.