A brief history of the VW flat-four engine

The longest-running production engine in the automotive world very nearly didn’t happen. Yet, the Volkswagen flat-four motor that lasted from 1936 all the way to 2005 has powered more types of car and other forms of transport than any other. Little wonder the humble air-cooled boxer four has become a legend. Here’s it’s story in a nutshell. 

It all started when Ferdinand Porsche realised post-First World War Germany needed a low-cost, durable family car. His engineering instincts were spot on and he was clearly inspired by Tatra’s flat-four design. However, needing a company to take on his plans and fund them, Porsche at first approached Zundapp, but the company had grand ideas about a radial five-cylinder engine that proved too expensive and complicated. 

From there, Porsche and his engine designer Josef Kales came up with an air-cooled unit for a project with car and motorcycle maker NSU. This also fell apart, but by then Porsche’s concept had caught the attention of Adolf Hitler, which led to the creation of the KdF-Wagen (Kraft durch Freude, or Strength Through Joy Car). Kales and Porsche batted back and forth designs for a two-stroke twin-cylinder engine and boxer twins before they alighted on an air-cooled flat-four. This became the Type 1 engine. 

Only a handful of the KdF-Wagen were ever produced prior to the Second World War, but the flat-four engine did find a use in the Kübelwagen. This utilitarian military vehicle also spawned a four-wheel drive variant, plus many others including some with a supercharger, turbocharger, and even a six-wheeler. More than 50,000 were produced during the war and the car then had a second life as The Thing in the US, also known as the Trekker in the UK. 

Post-war, Porsche’s notion for an affordable, simple car was more prescient than ever. However, it needed the vision of the British Army’s Major Ivan Hirst, who realised it was better for Germany to be helped back into work than be punished further for the hostilities. He convinced the British Army to order 20,000 of the new Volkswagen cars and by early 1946 the factory was making 1,000 per month. 

By this point, the flat-four engine’s design was settled. It used air cooling to keep it simple and cheap to produce, while the cooling fan had ducting to direct air around the pair of cylinder heads and barrels. A single camshaft operated both banks of cylinders. In this form, it produced a modest 25bhp from its 1,131cc capacity, but it proved reliable and easy to maintain. 

Porsche was not done with its involvement with the engine, either. Using experience gained with what was now known as the Beetle, though never officially called that by VW, Porsche went on to develop its 356 sports car range. These cars led on to the 550 and 718 models, plus the 912 and the mid-engined 914 that could all trace their power unit’s heritage back to the Beetle. 

The first major revision of the flat-four engine came in 1954 when its capacity increased to 1,192cc and power went up to 30bhp. That doesn’t sound like much of a jump, but it was a 20% improvement over the previous motor and the Volkswagen 1200, as it was known. For 1955, the Beetle’s trademark twin exhaust tailpipes made their first appearance. More updates arrived in 1957 with an all-synchromesh gearbox and power rose to a giddy 34bhp. 

The engine had also been used in the Type 2 Kombi bus, which used much the same engine as in the Beetle to begin with and then a 1.5-litre unit from 1964, followed by a 1.6-litre version for 1968. Other models from VW also stuck with the basic Beetle formula, including the Karmann Ghia of 1955 that had sports coupe looks but the standard and humble 1,192cc engine. It was the same for the 1500 and its Variant estate sibling that used a stock 1.5-litre version of the engine in 1961. However, the 1600S model gained an extra carburettor to free up 54bhp over the 44bhp that this engine offered when used on the Beetle 1303. 

The 411 and 412 models were an attempt by Volkswagen to compete with the likes of the Ford Cortina and Hillman Avenger. It stuck with the rear-engined layout but there was now a 1.7-litre motor with fuel injection that delivered 68bhp. From 1973, this was uprated to a 1.8-litre motor with as much as 85bhp. 

Elsewhere, Volkswagen’s flat-four engine had found favour with beach buggy and kit car makers in the fledgling 1960s component car scene. As the 1970s progressed, the Beetle and its easily tuned engine became the backbone of the kit car industry and remained through the 1980s, with hundreds of designs and companies coming and going. 

Before that, however, the VW flat-four had found another outlet for its immediately identifiable engine note as the power source for many aircraft. Experiments with the flat-four as an aircraft engine had started not long after the end of the Second World War thanks to its light, compact design and use of air-cooling. Several companies have modified the engine for aviation use and it remains a popular choice for those who value simplicity over outright performance. However, there are versions powering sports aircraft to more than 160mph, so it’s no slouch when required. 

As the Volkswagen Polo and Golf took over as the German firm’s mainstay models, the Beetle’s flat-four could have been put to rest in the 1970s. Instead, there was more development with a 60bhp 1.6-litre motor in 1971 to sit alongside the base 1300 version. US-bound cars gained fuel injection in 1975 to cope with that country’s tightening emissions laws. 

While the Beetle and its derivatives had come out of fashion in Europe and the US by the late 1970s, the car and engine’s original design brief proved ideal for other markets. The Beetle and Type 2 went on to be built in Brazil, Mexico, and Zimbabwe, and CKD (completely knocked down) kits were assembled in other countries including Australia, Indonesia, Ireland, Nigeria, South Africa, Thailand, and Yugoslavia. 

The final Beetle with an air-cooled flat-four engine left the factory in Puebla, Mexico in July 2003, while the last of this engine’s breed rolled off the Sao Paulo line in Brazil on 23 December 2005 fitted to a Type 2 microbus. By then, this engine’s place in history was not only assured, it was also a motor that changed history. 

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