Boxer H6 3.0R

Boxer engines got their name because each pair of pistons moves simultaneously in and out rather than alternately, like boxers showing they’re ready by clashing their gloved fists against each other before a fight.

A boxer, or flat engine, is an internal combustion engine with pistons that are all relatively horizontal. A straight engine canted 90 degrees from straight up is a flat engine, as is one in which the cylinders are arranged in two banks on either side of a single crankshaft. In both configurations, the motion of all the pistons is in the horizontal plane.
Usually, each pair of corresponding pistons from each bank of cylinders share one crank pin on the crankshaft, either by master/slave rods or by two ordinary rods side by side. Some authorities divide flat engines into boxer engines which do not share crank pins in this way, and 180° engines which do.
The boxer engine (also known as a horizontally opposed cylinder engine) in which the corresponding pistons reach top dead centeropposed piston engines, which use a completely different concept. simultaneously.

Flat engines are shorter than in-line engines, and have a lower center of gravity than any other common configuration, giving better stability and control. These engines, however, are also wider than more traditional configurations and are more expensive to build. The extra width may cause problems fitting the engine into the engine bay of a front-engined car owing to the interference with the steering wheels.

One benefit of using a boxer engine versus a V-engine is that the design provides good balance because each piston’s momentum is counterbalanced by the corresponding piston movement of the opposite side.

These engines can run very smoothly and free of unbalanced forces with a four-stroke cycle and do not require a balance shaft or counterweights on the crankshaft to balance the weight of the reciprocating parts, which are required in other engine configurations. Note that this is generally true of boxer engines regardless of the number of cylinders, but not true for all V and straight, or inline engines. However, in the case of boxer engines with fewer than six cylinders, unbalanced moments are unavoidable due to the “opposite” cylinders being not exactly opposite but offset slightly.

Boxer engines tend to produce more noise than inline and V-engines because valve clatter is not so well dampened due to lack of covering by air-filters and other components, and produce a larger torsional vibration than a V-engine, and so tend to require a larger flywheel. They have a characteristic smoothness throughout the rev range and, combined with the mounting position immediately ahead of the rear axle, offer a low center of gravity and more neutral handling.