Round Port header gaskets for Mark IV big block Chevrolet engines, constructed with a high-temperature expanded-steel core for strength, stability, and excellent torque retention under severe exhaust heat. The graphite-faced surface conforms to small flange irregularities, provides strong heat resistance, and helps transfer heat away from the cylinder head. The high-recovery material maintains a reliable seal even if the header flange loses clamp load, and the gasket can be trimmed for modified port applications. Suitable for OE replacement, performance street builds, drag racing, and oval-track engines.