Wiseco® Black Edition Piston Series is equipped with ArmorX piston coating and ArmorFit skirt coating adding superior protection in extreme conditions, reduced wear. Forged from high-silicon aluminum alloy for maximum strength and dependability. Feature forged pistons, rings, wrist pins and circlips. Smooth, quiet, and trouble-free operation. Improved flame travel to maximize air/fuel burn efficiency. Tool Steel Superfinish piston pin. Improved strength, reduced friction. Improved lubrication and better pin oiling, reduced friction. Augmented ring land details. Improved ring seal and function. Note: Cylinder sleeves must be purchased separately. Detailed Specifications: Bore diameter: 3.937. Compression ratio - actual: 10:1.