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What Makes a Boxer Engine

Updated: May 19, 2021

Although they are currently associated with Porsche and Subaru, horizontally-opposed "boxer" engines were once one of the most popular engine types, with lineage going back over 100 years. The first boxer was patented by automotive pioneer Carl Benz in 1897, and the design would go on to be adapted to all manner of early cars and motorcycles. Early airplane models also relied on horizontally-opposed flat-four engines, which continue to be used this day in small propeller-driven aircraft.

This Extra 260 stunt plane is powered by an 8.8 liter air-cooled flat-six.
This Extra 260 stunt plane is powered by an 8.8 liter air-cooled flat-six.

The boxer engine is fairly unique compared to the typical straight or V configurations, and offers its own advantages. The design takes an even amount of cylinders and lays them out 180 degrees, causing the pistons to punch outward in a boxing motion. These flat engines display exceptional smoothness of operation, and have almost zero vibration without a need for extra balancing components.

Boxers were also perfect for the mostly air-cooled vehicles of the early 1900's because the design puts the cylinder heads far away from each other and allows for maximum heat dissipation. V engines have the heads pretty near each other, which can cause cooling issues, although air-cooled V8s were also produced. Inline, straight engines, meanwhile, have a single cylinder head. That design had the poorest heat dissipation, ushering in the need for water cooling systems.

In performance cars, a flat engine offers the lowest possible center of gravity, since all the components are more or less on the same horizontal plane. Center of gravity is an extremely important metric for sports car and racing design, because putting all that mass down toward the ground allows for sharper cornering and more progressive weight transfer. We can see this handling prowess demonstrated in modern boxer-engined cars like the Subaru BRZ and Porsche Cayman.

One disadvantage of the design is that it's much wider than other engine types, presenting issues with packaging. The steering angle of front-engine boxer cars can be limited by suspension clearance problems, which is why many automakers, like Porsche, Volkswagen, Tatra, Chevy, Tucker, opted to mount the powerplant at the rear of the car.

This ultra-rare Tucker 48 sedan was created with a rear-mounted 5.5 liter flat-six sourced from a helicopter rotor.
This ultra-rare Tucker 48 sedan was created with a rear-mounted 5.5 liter flat-six sourced from a helicopter rotor.

There are some iconic boxer sports cars out there, chiefs among them being the Subaru WRX and the Porsche 911. The WRX sprung onto the scene in the late 90's as a rally homologation model for the Impreza sedan. Since then, the car has been a dominating force in rally racing, and a presence in almost every other form of motorsport. The first few versions were powered by a 2.0-liter turbocharged flat-four, which would later be punched out to 2.5 liters. The boxer design combined with exhaust geometry gives these Subarus a distinctive low growling sound which many enthusiasts prefer over typical four-cylinder buzzing.

The Porsche 911 traces its roots back much further, beginning as an upsized evolution on the 356 coupe, which itself was based on the common Volkswagen Beetle. Like the Beetle, the 356 was powered by an air-cooled flat-four which made horsepower in the mid double digits. When it came time for the 911 to replace it, Porsche created it's own single overhead cam flat-six which doubled power right out the gate. This original 911 chassis saw nearly 40 years of development, getting larger displacement, turbochargers, wide bodies, and all wheel drive, while still retaining the same basic body and air-cooled engine design.

By the late 90's, Porsche was the only high-end automaker still producing air-cooled engines, and the outgoing 993 was replaced by the modernized 996 generation, featuring a brand new chassis and a dual overhead cam water-cooled flat-six. This decision was very contentious at the time, although we should be able to agree it was a necessary change. Porsche had really hit the upper limit of air-cooled performance with the 993 Turbo, and they needed to make the next step.

Boxers may not have the most fans compared to old school V8s or high-revving inline fours, but they perhaps have the most dedicated fans. These flat engines bring a unique character to every car they power, and will hopefully be putting smiles on enthusiasts' faces for decades to come.

If you're looking for a prime example of boxer power, check out our 2021 Porsche Cayman GT4, which will soon be heading to auction.

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