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There's a Big Difference Between a Boxer and a Flat Engine

Internal combustion engines work in mysterious ways for the uninitiated. The earliest mechanism known to use a connecting rod and a crank is a device called the Hierapolis sawmill, a contraption that dates to the 3rd century AD. However, the internal combustion engine's genesis comes courtesy of Jean Joseph Etienne Lenoir, a Belgian that developed a gas-fired engine with connecting rods, pistons, cylinders and flywheel in 1860. That design wasn't without fault, but Nikolaus Otto did manage to invent a better mill that could burn fuel more efficiently.
180 degree flat engine vs boxer engine 1 photo
Since that seminal moment in 1862, the internal combustion engine slowly but surely catched on. It has become one of the most important utilities of modern living together with electricity and hot water. But despite it being with us since the mid-1800s, most people and even petrolheads still don't know that there's a very small but important difference between one of the most acclaimed engine architectures ever produced. Boxer engines should not be mistaken with flat V engines. Crank journals or crankpins, whatever you want to call them, these small devices attached to the crankshaft's big end bearings make the difference between a boxer and a flat motor. Simply put, the boxer mill employs one crankpin per cylinder, while the flat (horizontal V) engine uses one crankpin per two horizontally opposed cylinders.

A prime example of this automotive misconception comes in the form of the Ferrari Berlinetta Boxer. Even though its name suggests that is uses a boxer mill and the two six-cylinder banks oppose each other horizontally, that '70s Italian exotic uses an 180 degree V12 engine, not a proper boxer. By laying the angle of the V configuration to 180 degrees you don't necessarily transform the powerplant into a boxer engine 'cause the pistons and their connecting rods still share a crankshaft journal. See the image above? On the left you have a flat V configuration like the Berlinetta Boxer's mill, while on the right you have a proper boxer design with separate journals for opposed piston pairs.

Don't get us wrong, a flat engine is a mechanical masterpiece that makes proper gearheads go gaga. All V12 powerplants are inherently balanced regardless of bank angle because it employs two straight-six cylinder banks. At any given moment during the combustion cycle, an inline-six boasts with two pistons going down, two going up and two in the middle so there's no inbetween to unbalance the operation. But if you are that type of purist that cannot go with anything other than a true boxer, then the only way to go is Porsche or Subaru. Alfa Romeo made some very creamy boxer motors in its golden era, but that's not the case anymore under Fiat Chrysler Group's rule. If you're a motorcycle guy, BMW manufactures a truly remarkable and potent water-cooled boxer engine that propels the off-road/on-road GS series of bikes.

What about more common engine configurations such as the inline four-pot pretty much evey supermini, compact hatchback or sedan uses nowadays? This design is inherently unbalaced, but worry not. Vibrations that could shake the engine apart are dealt with things like a balance shaft or special flywheels that don't follow a perfectly circular path. Of course, there are other more hi-tech methods to offset the imbalance, but on a cheap and cheerful econobox that's not the case. If you still didn't quite get the difference between boxers and flat V motors, then take a look at the videos attached below. The first one shows you what's basically a Porsche 911 engine. The second is an animation of a flat V12 engine, in which horizontally opposed cylinders share a common crankpin.

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