L-4 Engine
Inline Internal Combustion Four-Cylinder Engine

The inline-four engines or the straight-four engine is a type of inline internal combustion four-cylinder engine with all four cylinders mounted in a perfectly straight line or plane along with the crankcase. The single bank of cylinders may be oriented either in vertical or on an inclined plane with all the pistons driving a common crankshaft. The place where it is inclined, it is sometimes called a slant four. The inline-four engines are listed either as I4 or L4.
The inline-four layouts are in perfect primary balance and confer a degree of mechanical simplicity which makes it popular for economical cars. However, despite its simplicity, it suffers from a secondary imbalance which causes minor vibrations in smaller engines. These vibrations become more powerful as engine size and power increase simultaneously, so the more powerful engines used in larger cars generally are more complex designs with more than four cylinders. Today almost all manufacturers of four-cylinder engines produce the inline-four layout, with Subaru and Porsche 718.