This comprehensive service manual is designed for Mercury Marine technicians and provides in-depth information for the Mercury Mercruiser 496 CID/8.1L #30 engine. It covers both Sterndrive (MCM) and Inboard (MIE) models equipped with the 496 Mag HO, 496 Mag, 8.1S HO, and 8.1S Horizon engines. The manual is structured to ensure easy navigation and understanding, with detailed information on various aspects of the engine, including critical maintenance procedures, troubleshooting tips, and step-by-step instructions for removal, installation, and repair. The manual begins with essential information encompassing general specifics, recommended maintenance schedules, and comprehensive troubleshooting guides. It then delves into detailed removal and installation procedures for both MCM and MIE models. The subsequent sections focus on the engine itself, providing a deep dive into the 496 CID (8.1L) engine. Further sections cover the electrical system, including the starting, ignition, and charging systems. The fuel system is extensively explored, with dedicated sections focusing on the electronic fuel injection delivery system and detailed disassembly and reassembly instructions. The manual also features sections dedicated to the cooling system for closed-cooled models, the exhaust system, covering manifolds, elbows, and collectors, and the drive system, which includes information on the Velvet Drive 5000 series transmission and the Hurth transmission. Lastly, it concludes with a section dedicated to the power steering pump.