A V4 engine is a four-cylinder piston engine where the cylinders share a common crankshaft and are arranged in a V configuration.
1990-2002 Honda ST1100 longitudinally-mounted V4 engine
1960–1994 ZAZ Zaporozhets aircooled V4
1963–1976 Lancia V4 engine
1970-1974 Ford Taunus V4 engine (in a Saab Sonett III)
A V engine, sometimes called a Vee engine, is a common configuration for internal combustion engines. It consists of two cylinder banks—usually with the same number of cylinders in each bank—connected to a common crankshaft. These cylinder banks are arranged at an angle to each other, so that the banks form a "V" shape when viewed from the front of the engine.
V-twin motorcycle engine (circa 1910)
V6 car engine (circa 1990)
V-angle illustrated by the yellow lines
Argus As 10 inverted engine