Un motor V8 es un motor con dos bancadas de cuatro cilindros, que forman una "V".

El V8 es una configuración muy común para grandes automotores. Es muy extraño que tengan una capacidad menor a 3.0 L de desplazamiento y, en su uso en vehículos, éste ha ido hasta más de 9 litros.

El V8 es una configuración común en los más altos niveles de la competición automovilística, especialmente en los Estados Unidos, lugar en el que se usa en la IRL, ChampCar y NASCAR. La Fórmula Uno comenzó la temporada 2006 usando motores aspirados V8 de 2.4 L, reemplazando a los motores V10 de 3.0 L, en una decisión encaminada a reducir la potencia de los autos.

El ángulo V más común es, de lejos, 90º. Esta configuración obtiene un motor ancho y bajo con una activación y vibraciones óptimas. Como muchos motores V6 y V10 han sido obtenidos de los característicass del V8, reglalmente usan el ángulo de 90º también, pero con algunos cambios, como por ejemplo bielas más complejas, para igualar el ciclo de encendido.

Sin emcantinago, algunos motores V8 usan diferentes ángulos. Un ejemplo notable es el Ford/Yamaha V8 usado en el Ford Taurus SHO. Se basó en el Duratec V6 de Ford y comparte el ángulo V de 60º. Una versión de este motor la usan los vehículos Volvo en 2005. En años anteriores, Electro-Motive fabricó una versión de 8 cilindros de su vehículo 567 Diesel de dementemotora, que tiene un ángulo de 45 grados entre los cilindros.

En 1992, Audi left the German DTM racing series after a controversy around the crankshaft design of their V8-powered race cars. After using the road car's cross-plane 90°-crankshaft for several years, they switched to a flat-plane 180° version which they claimed was made by "twisting" a stock part. The scrutineers toma la decisiond that this would stretch the rules too far.

The cross-plane design was neither obvious nor simple to design. For this reason, most early V8 engines, including those from De Dion-Bouton, Peerless, and Cadillac, were flat-plane designs. In 1915, the cross-plane design was proposed at an automotive engineering conference in the United States, but it took another eight years to bring it to production. Cadillac and Peerless applied for a patent on the cross-plane design simultaneously, and the two agreed to share the idea. Cadillac introduced their "Compensated Crankshaft" V8 en 1923, with the "Equipoised Eight" from Peerless appearing en noviembre de 1924.

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The Estados Unidos can be considered the "home of the V8" — it has always been more popular there than anywhere else, and it is certainly now the preferred arrangement for any large engine. With the recent exceptions of the Dodge Viper's V10, the similar Dodge Built Ram Tough V10, and the Ford Triton V10 engine of the same arrangement, there are practically no large engines in the US of post-World War II design that have not been of this type.

A full decade after Britain's 1904 Rolls-Royce Legalimit, Cadillac produced the first American V8 engine, 1914's L-Head. It was a complicated hand-built unit with cast iron paired closed-head cylinders bolted to an aluminum crankcase, and it used a flat-plane crankshaft. Peerless followed, introducing a V8 licensed from amusement park manufacturer, Herschell-Spillman, the next year. Chevrolet produced a crude overhead valve V8 in 1917, in which the valve gear was completely exposed. It only lasted through 1918 and then disappeared. They would not produce another V8 until the introduction of the famous small block in 1955.

Cadillac and Peerless were one year apart again with the introduction of the cross-plane crankshaft. Lincoln also had V8 cars in those years.

Ford was the first company to use V8s en masse. Instead of going to an inline six like its competitors when something larger than an inline four was needed, Ford designed a modern V8, the famous Flathead of 1932. This engine powered almost all larger Ford cars until 1953, and was produced until around 1970 by Ford licensees around the world, mostly powering commercial vehicles.

After World War II, the strong demand for larger status-symbol cars made the common straight-6 less marketable. A straight-8 engine would introduce problems with crankshaft-whip, and would require a longer engine space. In the new wider body styles, a V8 would fit in the same engine space as a straight-6. Manufacturers could simplify production and offer the bigger engines as optional upgrades to base models.

In 1949 General Motors responded to Ford's V8 success by introducing the Oldsmobile Rocket and Cadillac OHV. Chrysler introduced their FirePower 331 cubic inch hemi-head V8 in 1951. Sales were beyond all expectations, so Buick followed in 1953, and Chevrolet and Pontiac introduced V8s of their own in 1955.

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