A V engine is a common configuration for an internal combustion engine in which the pistons are aligned so that, if viewed along the line of the crankshaft, they appear to be in a V. The V configuration reduces the overall engine length and weight compared to an equivalent straight engine.
Various angles of V are used in different engines; depending on the number of cylinders, there may be angles that work better than others for stability. Very narrow angles of V combine some of the advantages of the V engine and the straight engine (primarily in the form of compactness) as well as disadvantages; the concept is an old one pioneered by Lancia, but recently reworked by Volkswagen.
Some V configurations are well-balanced and smooth, while others are less smoothly running than their equivalent straight counterparts. With an optimal angle the V12s and V16s have even firing and perfect balance. The V8s can be balanced with counterweights on the crankshaft. Others, such as the V2, V4, V6 and V10 show increased vibration and generally require balance shafts. In some configurations a special crankshaft is required to achieve even firing.
It is common for V engines to be described with V# notation, where # is how many cylinders it has:
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