Engine Overhaul Rebuild Kit 9.7:1 compression ratio includes piston ring set, bearings, and head bolts for use with 2005-2012 323i 523i E60 E90 E92 E83 E85 N52 2.5L engine models.Designed for engine rebuild applications, this kit provides essential components for cylinder head and bottom end restoration.The forged pistons are machined to precise tolerances with pre-installed ring sets.Full complement of main and rod bearings included.Head bolts are supplied to meet specifications for proper torque retention.All parts are balanced and matched for consistent performance.Intended for professional installation and complete engine reconditioning.