Its mostly a trigonometry thing, three sine waves 120 degrees out of phase balance out to constant torque. Also see electrical 3-phase power. Note that intern

Its mostly a trigonometry thing, three sine waves 120 degrees out of phase balance out to constant torque. Also see electrical 3-phase power. Note that internal combustion cylinder pressure is by no means a perfect sine wave LOL but its a close enough approximation to run smoother. Its partially a physics thing, in that ICE are usually 4-cycle so they fire every other rotation so if you want three firing pistons per rotation separated 120 degrees you'll need six cylinders total.