Tangential Treatise #4: Have You Ever Wondered What Makes Flat Engines So Special?


Today, Subaru is the only company in the world to use boxer engines and Porsche is the only other company to use flat engines. These engines feature cylinders that are neither inline nor banked at an angle to form a V-shape. Instead, the cylinders lay flat along a horizontal plane. But not all flats are boxers, even if all boxers are flats.

Ok, so that’s mildly confusing, but what are the advantages of this arrangement? And why do only two manufacturers employ the flat engine design? 

The advantage of having cylinders that are flat, or horizontally-opposed, is that cooling is ameliorated due to increased surface exposure between the cool air and the warm pistons. This was of particular advantage when engines were still cooled by air, instead of the liquid water that now cools everything every motor from that of a Lancia to a Lamborghini. Having a flat engine also lends itself to a lower centre of gravity because the engine occupies less vertical height. This lower centre of gravity in the engine as well as its lower height allow the engine to be placed lower in the engine bay. These advantages were clearly of great interest to Subaru when they chose to identify their company with flat engines and symmetrical all-wheel-drive. But considering that Porsche positions their engines behind the rear axle, in the trunk essentially, Ferdinand God only knows why they chose a flat engine. Oh, that’s right, Porsche does it because Hans Ledwinka did it first.

The difference between a flat boxer engine and a flat non-boxer engine is all in the crankpins. Whereas the boxer engines found in Subarus have individual crankpins controlling each cylinder, the non-boxers engines found in Porsches have opposing pistons sharing a crankpin on the crankshaft and therefore reach top dead centre a half crankshaft revolution apart. If that doesn’t mean much to you, watch the videos below to help you visualize the difference.

The flat engine design also boasts perfect natural balance and therefore does not require extra balancing weights the way other engine configurations do. Aside from the flat engine, only the inline-six and V12 are similarly balanced. The equipoise of the flat engine is achieved because the opposing pistons reach top dead centre simultaneously, thereby balancing each others momentum, as demonstrated below by Subaru’s elegant four-cylinder.

Beautiful, no? Well, it is doubly beautiful when compared to the chaotic clusterfuck seen in a Porsche’s flat engine.

The downside of boxer engines, and flat engines in general, is their affinity for yielding noise. Considered another way, flat engines have a distinctive guttural bellow that seems to appeal to enthusiasts, likely because this unique sound is associated with a car of potent performance (i.e. the Porsche 911 and Subaru STI) and is not associated with, say, a Prius, which is miserable and makes no sound at all. This is the main reason that more manufacturers don’t use flat engines – noise is the enemy in an automotive culture that reads “NVH” the same way followers of the Bible read “666”.

The design of the flat engine was originally patented by none other than Karl Benz, the man mistakenly credited with the invention of the automobile. This popular misconception can be attributed to the commercial pride of Daimler-Benz and as LJK Setright remarked succinctly “the furor Teutonicus of the Nazi party after coming to power in Germany in 1933”. The first man to manufacture a gasoline-powered internal combustion vehicle was actually an Austrian man of Jewish descent, Siegfried Markus. Markus built no less than four such inventions but unfortunately they were all for his own pleasure. Thus, Markus did not patent the motor vehicle despite holding 131 other patents, leaving the distinction of patenting the first automobile to Herr Benz. Wikipedia words it less poetically, although no less accurately, in saying “Markus was removed from German Encyclopedias as the inventor of the modern car, under a directive from the German Ministry for Propaganda during the Second World War. His name was replaced with the names of Daimler and Benz.”

Today, Markus is remembered by this statue in Vienna, Austria. Had I known about it this past summer, I might have visited the small monument to motoring (and Jewish) history. Instead, I saw a BMW 5-series GT, in a museum of all places. Oh, and a lovely Lancia too.

Despite the name of Benz being immortalized in popular culture and that of Markus being relegated to the cerebral cortexes of automotive historians, all on account of an anti-semitic smear campaign, Benz can be given credit where credit is due for the invention of the flat engine. Subaru and Porsche can at least thank Benz for that.

[Photo credit: Ricardipus/Flikr, deplaqer/Flikr]

[Video credit: author, YouTube]