Piston Ring Set 4.145 Bore File Fit

The MAHLE PISTONS Piston Ring Set 4.145 Bore File Fit (MPN 4145MS-112) is a premium performance ring set engineered for high-output engine builds requiring precision bore sizing and thermal stability. Designed for 8-cylinder applications, this file-fit ring kit delivers the critical compression seal and blow-by control that separates reliable power production from marginal performance in competitive and street-driven platforms.

The set features a three-piece ring geometry with 1.0 x 1.0 x 2.0 mm thickness specs and standard tension characteristics, paired with MAHLE's HV385 thermal treatment for enhanced durability under sustained high heat. The file-fit construction demands precision honing to the exact 4.145-inch bore specification, ensuring proper ring-to-bore clearance that minimizes blowby while preventing scuff and wear. Steel construction with thermal hardening provides the fatigue resistance necessary for forced-induction and high-RPM applications where conventional cast rings fall short.

This ring set is built for engine builders, racing programs, and enthusiasts undertaking serious engine recondition or custom builds where bore precision is non-negotiable. File-fit rings demand exacting machine work—bore preparation and honing to specification are prerequisites for achieving the sealing performance these rings are designed to deliver. The 4.145-inch bore sizing is common in performance big-block and small-block variants where displacement gains and durability demands require matched component precision.

MAHLE's long-standing reputation in OEM and performance ring manufacturing ensures this kit meets the metallurgical and dimensional standards that serious builders expect. The HV385 thermal treatment and steel composition address the specific challenges of modern high-compression, turbocharged, and nitrous-assisted engines where ring material properties directly impact reliability and ring life.