Keith black Hypereutectic pistons are made from 390 alloy and heat-treated to T6 standards, which makes them 30 percent stronger than ordinary untreated Hypereutectic. Their 100 percent CNC-machined crowns, high upper compression-ring location, gas-accumulator groove, drilled oil returns, and spiral-lock retainer grooves make these pistons outstanding for performance applications. They have a lightweight, rigid-rib skirt design that stabilizes the piston in the bore. All of this adds up to pistons that fit tighter than forged types, provide improved oil control, reduce blowby, increase ring life, eliminate cold start-up knocking, and won't cost you an arm and a leg