Inline four cylinder engine

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An inline-four engine is an ICE with four cylinders aligned in a straight line or plane within the crankcase. The cylinder bank can be vertically or incline-oriented, the latter sometimes referred to as a slant-four. Abbreviated as I4 or L4 (for longitudinal), the inline-four engine is popular for economy cars due to its primary balance and mechanical simplicity. Despite secondary imbalances causing vibrations that increase with power and size, it remains the most widely used four-cylinder configuration in modern vehicles, surpassing V6 engines as the second most common in late 2000s, especially amid efforts to reduce emissions and boost fuel efficiency. This trend has increased the proportion of new U.S. vehicles fitted with inline-four engines from 30% to 47% between 2005 and 2008, including mid-size cars where V6 options have decreased.