Many cylinders

One cylinder gives one bang per two revolutions — a rhythm you can feel shaking a moped apart. The cure is company: split the same total capacity into several cylinders and let them take turns. More cylinders means more, smaller bangs, more evenly spaced — and how you arrange them decides how the engine sounds, shakes and even where the car's bonnet line can sit.

The layouts

Inline — cylinders in a row, one bank, simple and cheap. The inline-four powers most of the world's cars; the inline-six is the smooth aristocrat (more on that below). V — two banks sharing one crank, folding the engine short: a V8 is barely longer than an inline-four. Flat (boxer) — the V opened out to 180°, pistons punching sideways at each other: low centre of gravity, the signature thrum of Subarus and 911s. V12 — two straight-sixes on one crank, the smoothest and most operatic of all, which is why Ferrari clung to it for decades.

The choice is packaging as much as physics: an inline-six is wonderfully smooth but long as a fence post; a V6 fits sideways in a hatchback; a flat-six sits low enough to hide under a sports car's tail.

Why engines shake

Every piston is a mass being hurled up and down thousands of times a minute, and Newton insists the engine block gets hurled the opposite way. Balancing is the art of making those hurls cancel. Pair pistons moving oppositely and their first-order shakes cancel; but remember lesson 3 — piston motion is not quite sinusoidal, so a subtler second-order shake (at twice engine speed) survives in some layouts.

The inline-four is the famous case: its pistons pair up nicely for first-order balance, but all four hurry over top-dead-centre together, so the whole engine buzzes vertically at twice crank speed. Big fours hide it with balance shafts — weighted shafts spinning at 2× crank purely to shake back. The inline-six needs none of it: its six throws are arranged so every order of shake cancels pairwise — inherent perfect balance, the engineering reason BMW built its reputation on sixes.

Firing order matters too: the bangs must be spaced evenly around the crank's rotation, and the chosen sequence (1-3-4-2 in most fours) also sets the exhaust pulse pattern — which is most of why a V8 burbles, a flat-four chugs and an inline-six sings.