Keith Black Performance Hypereutectic Piston For Harley FX / FL Keith Black Performance Hypereutectic Piston are manufactured from high-strength, T-5, heat-treated, 390 hypereutectic aluminum alloy. Features: Allow a tighter fit, longer piston and ring life Diamond-machined pistons are held to plus or minus on gram weight and less than .005 tolerances between pistons Each kit contains two pistons, pins, spiral-lock pin clips and Hastings moly rings Replacement piston rings and pin lock rings available separately These pistons can be installed tighter than other pistons, resulting in less piston rock and better ring seal. Special attention is required to the top ring end gap, refer to instructions for correct piston and ring installation Displacement Size CC: 1690cc Displacement Size CI: 103ci Cylinder Bore Size: 3.875 Compression Ratio: 10:1