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

Us car enthusiasts often associate engine layouts with certain makes and models. The V8 is regarded as the specialty of American brands due to passenger vehicle and truck applications from General Motors, Ford, Chrysler, and all those other companies that sadly left us for greener pastures. Flagship supercars sing the song of their people to the tune of 12 cylinders arranged in a V, and econoboxes rely on inline-four and inline-three mills. The flat engine, on the other hand, came to prominence with the start of series production of the VW Type 1, a.k.a. the Beetle.
180 degree flat engine vs boxer engine 11 photos
Photo: Frank Lente via Wiki Commons
Ferrari 512 TR flat-12 engineFerrari 512 TR flat-12 engine and transaxleFerrari 512 TR flat-12 engine and transaxleFerrari 512 TR flat-12 engine and transaxleFerrari 512 TR flat-12 engine and transaxlePorsche 911 S boxer enginePorsche 911 S boxer enginePorsche 911 S boxer enginePorsche 911 S boxer enginePorsche 911 S boxer engine
Used in a wide array of vehicles, including motorcycles and airplanes, the flat engine is called this way after its horizontally opposed cylinder banks. Emphasis on cylinder banks because there is a lesser-known layout known as the opposed-piston engine, a layout in which each cylinder features a piston at both ends and no cylinder head whatsoever. While compact and torquey, the 5TDF opposed-piston diesel in the T-64 main battle tank designed by Alexander Morozov is notorious for being very unreliable.

Turning our attention back to the flat engine, Karl Benz is credited with building the first example of the breed at the end of the 19th century. Ferdinand Porsche decided on a flat-four for the Beetle not only because he was fond of this layout, but due to the car that inspired the Beetle in the first place. That car is the Tatra V570 from the 1930s. The similarities between it and the Volkswagen are uncanny, and in the aftermath of World War II, the Czech manufacturer was awarded 1,000,000 Deutsche Marks for Porsche’s rip-off. But to his credit, Ferdinand perfected Tatra’s design.

Ferdinand Anton Ernest Porsche, as in Ferdinand’s son, is the gentleman who masterminded the 356. Similar to the Beetle designed by his father, the smooth-looking sports car uses flat engines due to their suitability for air cooling, short length, and low center of mass. The 356-replacing 911 also uses flat engines, although with six rather than four cylinders. But as you’re well aware, some people refer to these engines as boxers. Why is that?

Porsche 911 S boxer engine
Photo: Wob on Bring a Trailer
The big difference in the headline refers to how each pair of opposing pistons is connected to the crankshaft. Flat engines like those used in the 911 to this day are considered boxers because each pair of opposing pistons moves inwards and outwards at the same time. You can visualize the movement of the pistons in the first of two videos attached at the end of this story, or in the form of a professional boxer punching his gloves together before the start of the match. Also worthy of note, this engine configuration does not require a balance shaft or counterweights on the crankshaft.

The non-boxer flat engine is best considered a V-type engine with the cylinder banks arranged at 180 degrees. Each pair of opposed pistons shares a crankpin, whereas the pistons in a boxer feature individual crankpins. Because of this apparently small difference, one piston moves inward as the other moves outward in the non-boxer design. The second clip is an animation of a flat-12 comprising six pairs firing at every 60 degrees.

Italian mechanical Mauro Forghieri oversaw quite a few technical developments during his tenure at the Prancing Horse of Maranello. He’s the guy who developed Ferrari’s first flat-12 engine, the Tipo 207 used in the 1512 Formula 1 racecar. Despite a displacement of 1.5 liters, the 12-cylinder masterpiece produces approximately 220 ps (217 horsepower).

A few years later, Giuliano de Angelis and Angelo Bellei developed a flat-12 engine for street-legal cars. Codenamed F102, this powerplant made its debut in the Ferrari 365 GT4 BB, which couldn’t have arrived at a worse time. The oil crisis of 1973 limited production to 387 examples of the breed through 1976, when it was replaced by the more powerful 512 BB. Come 1981, the last of the series launched in the guise of the Ferrari BB 512i.

Ferrari 512 TR flat\-12 engine
Photo: calinsenciac on Bring a Trailer
As you already know from our piece on the 5 best supercars of the 1970s, the 365 in 365 GT4 BB is an approximation in cubic centimeters for each cylinder. 365 multiplied by 12 is 4.4 liters. GT4 means gran turismo and four camshafts, while BB stands for Berlinetta Boxer (even though it’s not a boxer mill), Berlinetta Bialbero (two camshafts), and Brigitte Bardot.

512 refers to 5 liters and 12 cylinders, although we’re actually dealing with 4.9 liters. The 512i, as you might have already guessed by now, marks the switch to Bosch K-Jetronic mechanical fuel injection. The K-Jetronic system made its production debut in the Porsche 911 T in January 1973.

Ferrari’s flat-12 dynasty continued with the Testarossa in the 1980s, a four-wheeled icon made famous in the hit TV series Miami Vice. The Italian automaker continued development of the flat-12 into the 1990s, first with the 512 TR. Because the Maranello series still wasn’t ready for production, Ferrari updated the flat-12 family one last time with the fugly F512 M.

On an ending note, it’s worth remembering that many automakers have used or experimented with flat engines. My father’s first new car, namely an Oltcit, had a two-cylinder flattie that would break down way too often. Nowadays, two automakers continue to pour millions over millions into this engine layout. The culprits are – no surprises here – Porsche and Subaru.

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About the author: Mircea Panait
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After a 1:43 scale model of a Ferrari 250 GTO sparked Mircea's interest for cars when he was a kid, an early internship at Top Gear sealed his career path. He's most interested in muscle cars and American trucks, but he takes a passing interest in quirky kei cars as well.
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