Inline6

An inline-six, or straight-six, is an internal combustion engine in which six cylinders are arranged in a single straight line along the engine block. Each cylinder houses a piston connected to a crankshaft, and the engine typically operates on the four-stroke cycle. The configuration can be naturally aspirated or turbocharged and is commonly found with overhead cam or single overhead cam cylinder heads.

The inline-six is renowned for its smooth operation, owing to excellent primary and secondary balance. This inherent balance minimizes vibration across a wide range of speeds, making the layout a traditional favorite for luxury, performance, and high-mileage applications. The long, linear arrangement also lends itself to simple cylinder head designs in some generations, though packaging varies by model.

A key drawback is packaging: the long, slender block is difficult to fit in transverse front-drive configurations, so inline-sixes are more often used in rear-wheel-drive or all-wheel-drive cars with longer engine bays, as well as in many trucks. They are popular in luxury brands and performance applications, with notable examples including modern turbocharged BMW I6 engines, the iconic Toyota 2JZ-GTE, and historical Jaguar XK engines.

Displacement typically ranges from about 2.5 to 4.0 liters in mass-produced road cars. While some applications have shifted to V6 engines for packaging efficiency, the inline-six remains valued for its smoothness, strong mid-range torque, and favorable high-RPM balance, especially in turbocharged variants.