A V12 engine is a v-shaped engine with 12 cylinders mounted on the crankcase in two banks of six cylinders each not always at a 60-degree angle to each other, with all 12 pistons driving a common crankshaft. Since each cylinder bank is essentially a straight-six which is by itself in both primary and secondary balance, a V12 inherits perfect primary and secondary balance no matter which type of V angle is used, and therefore it needs no balance shafts. A four-stroke 12 cylinder engine has an even firing order if cylinders fires every 60 degrees of crankshaft rotation, so a V12 with cylinder banks at 60 degrees or 180 degrees will have even firing intervals without using split crankpins. By using split crankpins or ignoring minor vibrations, any V angle is possible to operate. The 180-degree configuration is usually referred to as a flat-twelve engine or a boxer although it is, in reality, a 180 degree V since the pistons can and normally do.
These days the V12 engine seems to be a primarily British or German cuisine, with each likely considering themselves both curators and preservers of this dying recipe. Car manufacturers (exotics included) are shifting away from higher displacement engines, and towards more compact force-induced engines – all in the name of performance efficiency and satisfying stricter emissions regulations.
Aston Martin remains one of the biggest advocates for the V12, although many of its cars fitted with them also now have a V8 option that is usually not any less potent. British counterpart Rolls Royce has the honor of being the only automaker to have a v12-only-lineup of cars; a badge worn with pride, and perhaps some prejudice too.