Every V6 engine hides two unbalanced three-cylinder engines inside it
Split a V6 down the middle and each half is effectively a three-cylinder engine, and an odd number of cylinders in a row can never be perfectly balanced. So no matter how the banks are angled, a V6 shakes a little. Engineers tame it with dampers, balance shafts and clever crankshafts, because its compact size is too useful to give up.
That compactness is the V6's selling point. It is short enough to slot sideways into a front-wheel-drive car designed around a four-cylinder engine, making it the natural upgrade option, and it has become the most common layout for six-cylinder car engines. Luxury makers sometimes prefer a straight-six for its smoothness, and Porsche's 911 uses a flat-six for balance and a lower centre of gravity.
Six cylinders still beat four for smooth power. In a four-cylinder engine only one piston pushes at a time, leaving gaps between strokes. In an evenly firing six, each power stroke begins 60 degrees of crank rotation before the last one ends. Dynamometer measurements show a V6's torque swings roughly 154 percent above and 139 percent below average, against about 270 and 210 percent for a four.
Sixty degrees between banks is the ideal angle for balance and makes for a narrow engine. Lancia pioneered a six-throw crankshaft in its 1950 V6 to cut vibration. Many American firms instead chopped two cylinders off their existing 90-degree V8s, which saved design costs and let both engines share parts and production lines, at the expense of smoothness.
Early V6 engines were developed independently by Marmon, Deutz and Delahaye, and Buick brought one to its Special in 1962. Sizes usually run from 2.5 to 4 litres, though Mazda squeezed one down to 1.8 litres and GMC built a 7.8 litre giant for trucks. Volkswagen's VR6, from 1991, uses an angle of just 10.5 or 15 degrees under a single cylinder head; its name is German shorthand for a shortened inline engine.
Source: V6 engine
