Straight engine
Usually found in 4 and 6 cylinder configurations, the straight engine or in-line engine is an internal-combustion engine with all cylinders aligned in one row, with no or only minimal offset. The straight-4 is by far the most common 4 cylinder configuration, whereas the straight-6 is slowly giving way to the V6, which requires less space. Some manufacturers, such as Audi, VW or Volvo, also used straight-5 configurations.Straight configurations are simpler than their V-shaped counterparts and usually provide smoother running. There has been an advance by VW to combine the advantages of both configurations in an engine called VR6 (V to indicate the V shape and R for "Reihenmotor" (German for straight engine)). This was pretty much a V engine with a very narrow cylinder angle (15 degree), which allowed to combine the smaller size of the V6 engine with the smoother run of the straight-6.
Straight-6 engines can still be found in cars like the Australian Ford Falcon and the BMW 6-cylinder models.
