In this article we are diving into some technical details and the history of the famous air-cooled flat-six engines the Porsche brand has grown to be synonymous with. Porsche did not invent the ‘flat’ engine layout, neither were they the first to use air-cooled engines. But the way they applied both principles in the 911 was revolutionary and no other manufacturer has managed to match the performance and reliability Porsche manages to extract from their flat-six engines till date.
What is a flat-six engine?
The term ‘flat-six’ indicates that the engine is a boxer type engine with six cylinders, so the question now remains what is a boxer engine? In a boxer engine the pistons are laid out horizontally, the combustion process fires the pistons back and forth the cylinder in horizontal direction, almost looking like a boxer throwing a jab, hence the name ‘boxer’ engine layout. The benefit of a boxer engine layout is that it is flat and therefore has a very low centre of gravity compared to in-line or v-type engines. This low centre of gravity improves the overall balance and handling of a car.
The boxer engine characteristics also provide the driver with a lot of mid-range torque meaning the engine does not need to be high revving to produce its power, which aids reliability. The engine can also be build lighter, as fewer counter balancing weights are required within the engine. This is because the pistons are moving towards and away from the crankshaft at the same time, creating a natural balance of the rotating assembly. A by-product of this natural balance is the engine creates fewer vibrations and runs smoothly. It also produces the distinctive soundtrack we all know and love from boxer engines.
The history of the boxer engine dates all the way back to 1896, when Carl Benz first came up with the idea. Porsche joined the flat-engine fray in 1947 when Ferdinand Porsche put a Volkswagen Beetle four-cylinder boxer engine into his Porsche 356 which had the engine sitting over the rear axle. He liked the simplicity and driving characteristics of the car and engine so much that it became the base upon which Porsche built its cars for many years to come.
What does air-cooled or luftgekühlt mean?
The air-cooled aspect of the engine really is as simple as it sounds, it works by using air and only air to directly cool the engine. The alternative and more common method is using a water-cooled engine which contains coolant fluid that runs through circuits in the engine and through a radiator which eventually uses air to cool the fluid which in turn cools the engine. Water-cooled engines require lots of extra parts like a reservoir and a circuit of hoses to hold the coolant fluid and to connect all the different parts of the cooling system, a water pump is needed to move the coolant fluid through the circuit and radiators are used to cool down the fluid. This all adds complexity and weight.
So when Porsche was looking for a new engine for the 356’s successor the idea of having fewer parts (meaning less weight), less complexity, more reliability, and therefore less cost was a perfect match with the goals that Porsche had in mind. This eventually led to the first 2.0 liter flat-six air-cooled engine developed by Porsche.
An air cooled engine’s lifeblood is the oil circulating within it, the oil lubricates the engine’s internals but also plays a big role in cooling. The oil in an air-cooled engine is pumped around the engine block and then goes out to the oil cooler(s), which are located directly into the airflow allowing the air to cool down the oil and to flow back into the engine once it has cooled. There are additional fans (driven by the auxiliary belt or electrically) to aid cooling when the car is not moving. The pistons of an air cooled engine run through so called ‘cylinder barrels’, which in are held in place between the crankcase and the cylinder heads. The cylinder barrels and cylinder heads have fins on them to allow heat to be dispersed much more quickly than if it were a solid piece of metal (the same principle as a radiator).
History of the air-cooled flat-six engine
Okay so while Ferdinand Porsche was fiddling with his 356 he discovered a formula of applying a flat-six air-cooled engine over the rear axle of a car. This formula became the base for the 356’s successor which was first called the Porsche 901, however Peugeot got angry because they had patented the type designation consisting of three-digit numbers with a zero in the middle, so Porsche renamed the 901 to the 911, which we still use nowadays. But what made the 911 so incredibly successful as a sports car?
Like mentioned earlier the flat-six engine was the ideal choice to fit the Porsche 911’s sporty driving style by creating a very low center of gravity. Mounting the flat-six engines all the way in the back of the chassis also allowed for greater traction when accelerating because the weight of the engine puts extra downward pressure on the rear tires. The original 911 model introduced in 1965 was well received among sport car enthusiasts and because of the success, the formula of using the flat-six air-cooled engine mounted over the rear axle remained unchanged for over 3 decades. The engines were of course updated and revised to meet emission standards and deliver higher power outputs throughout the years and generations. Only with the introduction of the 996 generation in 1998 did Porsche stray away from the traditional air-cooled engine design. However the flat-six layout is still used by Porsche until this date, but the engines are now water-cooled, reason being that the air-cooled engine design was just too difficult to make compliant with ever evolving emissions laws.
The EPA and EURO testing procedures measured emissions within a set timeframe after startup from cold and since air-cooled engines take longer to warm up than water-cooled engines, Porsche was at a major disadvantage since the engine wasn't warm by the time the readings were taken.
The ending of the air-cooled 911 era has caused the Porsche 911 993 produced from 1994-1998, and Porsche 911 964 produced from 1989-1994 to become some of the most sought-after models since they were the last to use the legendary traditional air-cooled engines. The air-cooled flat-six’s still have a massive fanbase to this day and will remain a pinnacle in Porsche’s history.
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