fourcylinder

Fourcylinder refers to an internal combustion engine that uses four cylinders to convert the energy from fuel into mechanical work. The most common arrangement is the inline four (I4), where all four pistons move in a single line. A less common variant is the flat or boxer four, in which two opposing banks of cylinders lie on opposite sides of a flat crankcase. Four-cylinder engines typically operate on the four-stroke cycle—intake, compression, power, and exhaust—and can run on gasoline, diesel, or alternative fuels, with many modern designs using spark ignition and direct fuel injection.

The inline-four layout is valued for its simplicity, compact size, light weight, and cost efficiency, making it the dominant engine configuration in mainstream passenger cars. Advances such as dual overhead camshafts, variable valve timing, turbocharging, and direct injection have substantially increased power output and efficiency within the four-cylinder class. Turbos, in particular, allow four-cylinders to deliver higher performance without the weight and size penalties of multi-cylinder engines.

Disadvantages of four-cylinder engines include greater vibration and noise in certain designs compared with larger engines, particularly at high loads. Some configurations employ balance shafts or other NVH measures to improve smoothness. The flat-four offers a lower center of gravity and improved lateral stability but is wider and can complicate engine bay packaging.

Four-cylinder engines are widely used in a broad range of vehicles, from economical subcompact cars to performance-oriented models, and they also appear in motorcycles and light aircraft. They remain a foundational technology in modern internal combustion propulsion.