Boxer Vs. Flat Engines: Why They're Not The Same And Here's What Sets Them Apart

A stark contrast in design philosophy separates boxer and flat engines, with the inherent advantages of one ultimately rendering the other obsolete

by Dimitar Angelov on August 14, 2024, 09:00

Boxer and flat engines are a highly-uncommon sight in the modern-day automotive industry. Currently, there are only two manufacturers that continue to produce and develop boxer engines – Subaru and Porsche. The boxer engine is most commonly characterized by its flat design hence it is, often, referred to as a flat engine. The first boxer engine was developed in 1897, by Karl Benz – the co-founder of what would eventually become Mercedes-Benz. There is a common misconception when it comes to these engines. Boxer and flat engines are not quite the same. All boxer engines are flat engines, but not all flat engines are boxer engines. This misconception comes from the 1973 Ferrari 512 Berlinetta Boxer. Despite the name, it does not feature a boxer engine, but rather a flat-12 engine or a 180-degree "V-engine". Boxer and flat engines are more different than you think, and here is what sets them apart.

Difference between boxer and flat engines

Boxer Vs. Flat Engines: Why They're Not The Same And Here's What Sets Them Apart storyboard - image 190284 — In a boxer engines, every pair of opposing pistons mirror each other’s movements, resulting in smoother operation

Structurally speaking, the main difference between boxer and flat engines is the number of crank pins. In a flat engine, each pair of opposing pistons shares one crank pin, similar to a V-shaped engine. In a boxer engine, each piston has an individual crank pin. Both engines feature horizontally-opposed pistons, at a 180-degree angle, but that’s where the similarities end. In a flat engine, when one piston is in stroke one, one on the opposite side is in stroke two. In other words, when one piston is in the top dead center, the one on the opposite side is at the bottom dead center. In a boxer engine, each pair of opposing pistons mirrors each other’s movement, so when one is in stroke one, the one on the opposite side is also in stroke one.

Why boxer engines are better

Boxer Vs. Flat Engines: Why They're Not The Same And Here's What Sets Them Apart storyboard - image 187050

The traditional flat engine has long been discontinued, leaving boxer engines as the only type of flat engine still made for vehicles. Subaru even made a six-cylinder boxer engine that rivaled some of Porsche’s mills, although nowadays, the brand focuses on developing flat-four engines. This leaves Porsche’s iconic boxer engines as the only flat-six units in the automotive industry. With each piston mirroring the movements of the one on the opposite side, they cancel each other’s forces out. It looks like two boxers trading punches, hence the name. This type of movement drastically reduces engine vibrations that would otherwise be transmitted into the cabin. Thanks to Porsche and the T-Hybrid powertrain in the 992.2, we now know boxer engines work great as part of a hybrid setup.

This means that boxer engines are much smoother compared to other flat engines and even conventional, inline, or V-shaped engines. All flat engines are more expensive to make due to the need for more parts. That said, this is one of the few instances where the more cost-effective flat engine gave way to the more expensive boxer engine. The boxer engine features twice as many crank pins, making it even more expensive than the flat engine. However, this also results in much smoother operation, effectively making the traditional flat engine obsolete. That said, no engine layout is perfect and the boxer engine has its fair share of pros and cons.

Boxer engines: The good and the bad

Boxer Vs. Flat Engines: Why They're Not The Same And Here's What Sets Them Apart storyboard - image 187853

Pros	Cons
Smooth operation	More complex
Better fuel efficiency	More expensive to service
Added safety	Heavier compared to an equivalent conventional ICE
Low center of gravity	Larger packaging due to engine width
Less powertrain loss

Dimitar Angelov

Dim has been an automotive journalist since 2014. Although he is interested in all things automotive, his main interests revolve around, Asian, classic, and sports cars. He is particularly fond of Porsche sports cars as well as JDM classics from Toyota, Nissan, Honda, and others. Dim operates mainly from Bulgaria, but can, occasionally, be seen attending Europe's most reputable Auto shows, and events. Read full bio