straightsix

Straightsix, or straight-six, refers to an internal combustion engine with six cylinders arranged in a single straight line along the crankcase. It is commonly called an inline-six or I6. Cylinders share a common crankshaft, and many designs employ overhead camshafts; engines exist for both gasoline and diesel use.

The inline-six is widely regarded as one of the smoothest engine configurations. The six cylinders in a straight line provide strong primary and secondary balance, reducing vibration and often eliminating the need for balancing shafts. This smoothness makes it popular in luxury and performance cars, though it creates a longer engine block that can complicate packaging in smaller or transverse-mounted layouts.

Disadvantages include its length, which can complicate transverse mounting in front-wheel-drive designs and limit packaging in compact cars. It is generally heavier than a comparable four-cylinder and can be more expensive to manufacture. Modern implementations often combine the six with turbocharging or diesel technology to improve efficiency and power without sacrificing smoothness.

Historically, the straight-six has been associated with European and Japanese brands. Notable examples include the Jaguar XK engine, BMW inline-sixes such as the M30 and M54 families, Nissan's RB26DETT, and Toyota's 2JZ-GTE. Today, turbocharged inline-sixes remain common in some luxury sedans and performance models, and diesel variants are found in trucks and larger cars.

Although production of new straight-sixes has declined in some segments due to packaging constraints and the rise of smaller four-cylinder engines, they remain valued for refinement and steady, linear torque in appropriate applications.