Straight-four engine

13–16  (with the exceptions of the flat-four engines produced by Subaru and Porsche)[2] and the layout is also very common in motorcycles and other machinery.

When a straight-four engine is installed at an inclined angle (instead of with the cylinders oriented vertically), it is sometimes called a slant-four.

European and Asian trucks with a gross vehicle weight rating between 7.5 and 18 tonnes commonly use inline four-cylinder diesel engines with displacements around 5 litres.

The strength of this imbalance is determined by the reciprocating mass, the ratio of connecting rod length to stroke, and the peak piston velocity.

182–185 Many cars produced for the pre-WWII voiturette Grand Prix motor racing category used inline-four engine designs.

1.5 L supercharged engines found their way into cars such as the Maserati 4CL and various English Racing Automobiles (ERA) models.

These were resurrected after the war, and formed the foundation of what was later to become Formula One, although the straight-eight supercharged Alfettas would dominate the early years of F1.

The 1986 version of the engine was said to produce about 1,300 hp (950 kW) in qualifying trim, at 5.5 bar of turbo boost.

[22] The first across-the-frame 4-cylinder motorcycle was the 1939 racer Gilera 500 Rondine, it also had double-over-head camshafts, forced-inducting supercharger and was liquid-cooled.

The modern Triumph company has offered inline-four-powered motorcycles, though they were discontinued in favour of triples.

Instead, it uses a crossplane crankshaft that prevents the pistons from simultaneously reaching top dead centre.

This results in better secondary balance, which is particularly beneficial in the higher rpm range, and "big-bang firing order" theory says the irregular delivery of torque to the rear tire makes sliding in the corners at racing speeds easier to control.

Inline-four engines are also used in light duty commercial vehicles such as Karsan Jest and Mercedes-Benz Sprinter.