Luftgekühlt — Porsche’s Long Embrace of Air-Cooled Engines

February 21, 2022

Porsche has always been a bit of an enigma. It is the most successful sports car builder in history, with more than one million 911s produced, and more race wins than one can count. Yet, the German company stubbornly stuck with the seemingly primitive designs long after it seemed like they were a wise idea. 

Case in point: the air-cooled engine which is referred to by those in the know as Luftegekühlt, German for air-cooled (pronunciation). Porsche took a dictator’s demand for a car that worked in winter and, with ingenuity and sheer stubbornness, evolved the air-cooled engines into high-performance lumps that have earned their own rabid following. (Would that be a Luftgekühlt cult?)

Let’s explore the history of Porsche’s air-cooled engines, why the company held on to them, and then why they retired them in the 1990s.

It Started with Volkswagen

Internal combustion engines create power from fuel combustion, which creates pressure to generate kinetic energy. The by-product is heat -- a lot of it -- which, if not removed, can cause engine failure. 

The very first gas-powered automobile built by Carl Benz in 1886 used water cooling to dissipate heat from the single-cylinder engine. It took a few more years for radiators to show up when, in 1897, Wilhelm Maybach developed the tubular radiator that flowed water through a snaking pipe to cool it down. An overwhelming majority of automobiles from that time on relied on water cooling through radiators. For good reason: water conducts heat away from metal 175 times more efficiently than air.

Enter Ferdinand Porsche and Adolf Hitler. Along with his highway system, Hitler dreamt of a utilitarian and affordable car and asked Ferdinand Porsche to design “the people’s car” in 1934, known initially as “Project 60.” Along with his son Ferry, Porsche came up with the core concepts which included an air-cooled 4-cylinder boxer engine mounted in the rear. 

There were two key reasons for using an air-cooled engine: ease of maintenance and winter weather. In those days not everyone had access to a garage, so this design meant fewer parts for easier maintenance and repair. More directly to the point is that water freezes, and in those days anti-freeze was not yet used in automobiles. Taking water out of the equation meant the Volkswagen could operate trouble-free through the harsh German winters. (Also the reason the engine was mounted in the rear for better traction.)

While seemingly simplistic and anachronistic, it was functional and fit the design specifications perfectly. The Volkswagen Beetle started production before the war and then resumed immediately afterward as part of the reconstruction. 

The Porsches had only designed cars for others, but now they were ready to launch their own car: the 356 Roadster, which went into production in 1948 (pictured above). The engine was a lightly tuned Volkswagen engine, fitted into a lightweight body with a nimble suspension.

Porsche grew quickly and built a reputation on the tracks of Europe, including class wins at Le Mans in 1951 and Carrera Panamerica in 1952. The 356 engines were getting more powerful through more displacement, upgrades to cylinder heads, camshafts, crankshafts, intake and exhaust manifolds, and dual carburetors. 

1968 Porsche 911R Engine (Porsche)

Along Comes the 911

In the early 1960s, it was time for an upgrade. The Porsche 911 was first shown in 1963 and went into production in 1964. The 911 engine, designed primarily by Hans Mezger, added two more cylinders that increased the displacement to 2.0L, but the design was quite similar to its predecessor. The main upgrade was the addition of a fan to drive airflow over the engine for better efficiency. To better control heat, the 911 added oil cooling and utilized aluminum for the major components, which is much more efficient in conducting heat.

Porsche continuously evolved the 911, adding fuel injection in the 1970s and steadily increasing displacement. The biggest improvement arrived in 1975 with the addition of a single turbocharger that cranked out 260 hp in a 3.0L displacement. In 1978, Porsche was the first to use an intercooler in a production car to further improve the turbo’s performance. 

The ultimate evolution of the Porsche air-cooled engine was 2.8L flat 6 in the revolutionary 959 supercars. The slippery 959 took on the world’s best when introduced in 1986, with its twin turbochargers and double-overhead cams housed in water-cooled heads. The result was a whopping 444 hp driving all four wheels.

By the 1990s, the air-cooled design was reaching its technical limits. In a move considered heretical by many Porschephiles, Stuttgart closed the air-cooled era in 1997 after 50 years, and launched the water-cooled era with the 996.

Pros and Cons of Porsche’s Air Cooling

One has to admire the success of Porsche in engineering workarounds for air cooling and rear-engine design. Stuttgart’s continuous evolution did the seemingly impossible of overcoming inherent problems and turning them into world-class machines, both on the road and on track. 

The air-cooled cars are still considered the best produced by many aficionados. On the other hand, it is possible they were just too stubborn and stuck in their ways. How much further could they have gone had they adopted more efficient cooling and a mid-engine layout earlier? Following are a few reasons for and against the humble air-cooled engine.

Pluses

Lower mass and center of gravity. Air-cooled engines have compact designs that can sit lower in the car, a big advantage in performance driving situations. The boxer configuration that Porsche utilized was also critical in putting the center of gravity as low as possible.

Easier maintenance. The cooling is from fins and fans, rather than radiators, pumps, hoses, and coolant. This means fewer parts and fewer things to go wrong. (Ask any British car owner what percentage of breakdowns are due to coolant systems!)  Because of the wider temperature range, parts are built more sturdily and with greater tolerances. 

911 Piston and Finned Cylinder

Modular design. Porsche’s air-cooled 6-cylinder engines use 16 different castings, whereas it is more common to have two in most engines (the block and the head). If a piston fails, one can swap out that cylinder without tearing down the entire block, quite a difference in cost and time than most cars.

Reliability. As long as one keeps up with the maintenance, these engines are built to last. So much so that they were the standard for endurance racing for decades.

Lower drag. Radiators are efficient as heat exchangers but are decidedly inefficient aerodynamically, so air-cooled cars don’t need big front grills or ducts to pull air over a draggy radiator. 

Great sound. Porsche’s air-cooled engines, especially the flat sixes, have a distinctive, heart-stirring sound. (Want proof?) In water-cooled engines the liquid-filled jacket absorbs sounds, but that is definitely not the case in an air-cooled engine which emits more decibels -- in a good way when driving, but maybe not so good for the neighbors.

Minuses

Less efficient. The temperature range is much wider in air-cooled engines, which means the fuel mixture burns differently. On startup, air-cooled engines stay cold longer. The cooler temperature affects how the fuel mixture vaporizes that can result in inefficient fuel combustion. This is more of an issue in earlier models, as the introduction of Bosch fuel injection and electronic sensors made this less of a problem. 

Higher emissions. From the 1970s on, when air pollution became a concern, the less efficient combustion resulted in more pollution. Porsche had to continually fight to keep the cars compliant and was adding devices to minimize tailpipe emissions.

The Demise of Luftgekühlt

The demise of the air-cooled engine wasn’t due to any inherent flaw, as Porsche proved time and time again. It just wasn’t able to keep up with the competition’s performance gains. In the 1980s, the competition for sports and supercars was heating up with horsepower creeping toward 500 hp and beyond. 

Where others were gaining performance by increasing the breathing with four valves per cylinder, which enabled better airflow and higher RPMs, air cooling was not able to keep up because that level of power generated unbelievable amounts of heat that needed to be dissipated. It was possible with exotic materials and tech to take horsepower higher in air-cooled engines, but it would not be commercially viable. The iconic Porsche 917 from the early 1970s had already reached 500 hp with a flat V-12 that was air-cooled, but it took NASA-level material science and a complex engine to do so.

In the end, Porsche realized that sticking with old-school air cooling was going to hurt them in the market. So they made the tough call to move to water-cooled engines. They may not have the charm or tradition, but the 996 engines and beyond extended Porsche's performance to new heights.

Nevertheless, the Luftgekühlt engines deserve a place in any Engine Hall of Fame. Contrary to all conventional wisdom, Porsche was able to take the humble air-cooled engine and evolve it into a world-beater. For many, there is no substitute for air-cooled.

References

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