MAHLE 3150005-005 Plasma-Moly Piston Ring Set 4.005 in. Bore File Fit 8-Cylinder

The MAHLE 3150005-005 is a plasma-moly, low-tension, file-fit piston ring set engineered for 8-cylinder engines with a 4.005-inch bore (+.005" oversize). Built from SAE 9254 carbon steel and featuring MAHLE's proprietary plasma-moly face coating, this ring set is designed for street, racing, and marine applications that demand maximum sealing, reduced friction, and long-term durability under high-RPM, high-compression conditions.

Key Features:

• Plasma-Moly Top Ring: Barrel-faced top ring provides instant break-in and maintains consistent contact with the cylinder wall as the piston rocks at TDC and BDC
• Napier THG Second Ring: Tapered hook groove (THG) second compression ring delivers superior oil control by scraping cylinder walls and creating an oil reservoir on each down stroke
• CP-20 Oil Control Ring: Named for its 20-degree ear angle, the CP-20 provides an exceptional cylinder wall seal for maximum oil control
• Low Tension Design: Reduces parasitic friction losses to free up horsepower and improve efficiency
• File Fit: Allows end gap to be precisely set for a custom fit to your specific application
• SAE 9254 Steel Construction: Delivers superior tensile strength, hardness, and fatigue resistance compared to cast iron alternatives
• Ring Widths: 1/16 in. (top) × 1/16 in. (second) × 3/16 in. (oil)
• Sold as a complete set for one 8-cylinder engine

MAHLE's plasma-moly coating extends ring life, eliminates ring breakage, reduces side wear, and minimizes groove pound-out — all critical factors in high-output performance engines. The smaller ring cross-section moves the top ring groove closer to the crown of the piston, reducing crevice volume and unburned fuel emissions while improving the ring's ability to conform to cylinder bore distortion common in high-RPM builds.