This is the fascinating history of Stuttgart’s superb engines and the sporting supercars they powered in the 1920s and early 1930s. Although these monstrously capable machines are often nicknamed “Porsche-Mercedes”, in fact this tells less than the full story. While the legendary Ferdinand Porsche was closely involved with their development, the pedigree of these amazing vehicles was established well before Porsche joined the company, and would persist for years after he left.

Recovering from war

These charismatic engines were conceived – though not engineered – in 1919, when Mercedes set out to recover from the trauma of the First World War. Germany’s economy and standing in the world had been smashed, and the flower of a generation had perished in the trenches. 

Technical boss Paul Daimler saw to it that pre-war models like the 28/95 were ushered back into production. However, he also benefitted from the experience his company had gained in the air during the 1914-1918 conflict. Daimler began development of the firm’s new post-war automobiles with the first of a series of supercharged engines. Two large road cars were previewed at the Berlin Motor Show in 1921. At the same time, a 2.0-liter eight-cylinder supercharged engine was developed for motor racing, where it soon became conspicuously successful.

Enter Porsche 

Paul Daimler then decided to retire, and the firm immediately replaced him with an already-controversial figure, Ferdinand Porsche. As a noted historical authority from that period, Richard Langworth, wrote, "Porsche immediately settled down to work on a series of large supercharged models, his principal achievement at Daimler." This is an ideal summary of Porsche’s lasting influence at Stuttgart. Although Porsche remained at Mercedes-Benz until 1928 and ushered in more modest models such as the Stuttgart and Nürburg ranges, it was his series of magnificent new supercharged machines, and the later supercharged engines inspired by him, for which Ferdinand Porsche will always be remembered.

The chassis of these cars, first seen in 1924 and last used in 1933, was conventional enough, with massive channel-section side members and front and rear beam axles. Front suspension was by half-elliptic leaf springs; the rear used cantilever springs. Over the years there was to be a wide choice of coach-built bodies, open and closed, some built in-house in Sindelfingen, others from well-respected outside builders. The constant feature of this ever-developing range was that the vehicles, their engines, and their ambitions were all big. Very big.

Supercharged big sixes

Here we will concentrate on the evolution of the big six-cylinder engines themselves, power plants that had no previous history at Daimler or Benz. Nor did they have any credible rivals. These thundering internal combustion monsters would be looked on with awe by engineers at competing companies.

The very first of these was installed in the original Mercedes 24/100/140, not a racing car, but a street vehicle with all of the company’s – and Porsche’s – technical know-how built in. It was a long-stroke 6,242cc engine (the 150mm stroke would not change in a nine-year span) and, surprisingly, there was a light-alloy cylinder block, topped by a cast iron cylinder head, overhead valves, and a single overhead camshaft operating the valves with finger followers. In the future, the automotive industry would become familiar with all those features. 

However, only 100 horsepower was available from 6.2 liters – merely adequate even by the standards of the mid-1920s. The supercharger was clutched into engagement at the driver’s command, adding an additional 40 horsepower.

Add Leichtheit

One of Porsche’s tasks was to make the next vehicle lighter and more powerful, which explains why the result, first seen in 1928 was the 24/110/160, or K-Type. The K stood for Kurz, German for short. Lighter was also a relative term, for the new car's wheelbase was still an impressive 11-ft. 2-in. (340cm). For short bursts with the supercharger engaged, up to 160 horsepower was claimed, which delivered a top speed close to 100 mph.

It was a start, but Porsche did not think it enough. Even though sales were slow, he and his team were allowed to develop a successor to the K.  Christened the S-Type, it carried a more powerful version of the engine within a re-engineered chassis. The new model was much lower, structurally stiffer, and with proper half-elliptic leaf spring rear suspension. The engine was  also moved back in the frame by twelve inches, which reduced the kind of body styles that could be offered.

Watch that S-Car go

The engine had again been reworked, this time with a 98mm cylinder bore, and now with a supercharger-engaged peak power output of 180 horsepower. This ensured that the new model was not only fast, but very flexible, for it could crawl along in top gear at snail's pace, but with supercharger engaged it could almost top the 100-mph mark. Incidentally, the factory-prepared racing models with higher compression ratios and special fuels turned out at least 220 horsepower. It was that type of car in which Otto Merz won the German Grand Prix of 1927. Only 149 S-Type cars were ever made.

When England’s The Autocar magazine sampled an S-Type near the end of 1928, the headline read, "Flashing Acceleration and Instant Responsiveness,” though the article did not actually quote any figures. Perhaps that would have been undignified for such an expensive vehicle. In the UK, the Mercedes was more costly than the contemporary Rolls-Royce 40-50hp. Still, Douglas Clease, who penned the words, was inspired to write:

“Engage first gear, accelerate gently as you let in the clutch, and then force the accelerator pedal right down to the floor boards. With an increasingly shrill whine the blower comes into action, and the back of the seat seems to hurl you through space. Change to second gear, and you can repeat the performance if the road be open, that is, for you will be moving at a rate of a mile a minute before you have recovered your breath.”

At this point I should pause to explain that by today’s standards this engine might seem woefully inefficient, but back then, it was state-of-the-art. In its day, S-Type was probably the fastest road car in the world, and one of the most expensive, roughly the equivalent of today’s 640 horsepower AMG GT Coupe. Both cars were regarded as ultra-exclusive, which explains why production was so limited.

Economists on the Board of the Daimler-Benz parent company probably winced every time they looked at one of these Porsche-engined cars. Perhaps only one vehicle could be hand-built by craftsmen every week. But as this was the company's flagship model, such indulgences could be accepted.

The SS & SSK

It was clear that Porsche did not really care about the financial bottom line. As a final fling before he left the company, he and his team indulged in a bit of even more carefree one-upmanship. In 1928 they delivered the next evolution, the SS-Type with an engine which had once again been enlarged, now to 7,069cc. 

In the same season there was to be an even more specialized derivative called the SSK (or 27/170/225), which showed that the engine had been yet further boosted for its new application.

Although by this time the engine had reached the limits to which it could be stretched, it was not the last time that even more power would be squeezed out of it. Given time and a generous development budget, the team had produced tubular connecting rods, aluminum pistons, a higher compression ratio, and larger valves for the cast iron head. In the SS, the compression was further increased and detail changes to breathing carried out. 

This was done for the road car engines, but in specially-developed form they had not yet reached the end of their potential. In some configurations, such as the works competition cars, the supercharged engine could be pushed up to 300 horsepower and beyond for short-endurance motorsport. By late 1920s standards this was a phenomenal figure, and major competitors like Bentley struggled to keep up.

Birth of the SSKL

After Porsche left the firm there was little more progress to report. The SS remained the company's supercar-in-residence for five years, until 1933. Yet only 114 such cars were ever produced. In the meantime, the company used the 7.1-litre SS as the basis for the specialized SSK, and an entirely impractical road-car offshoot called the SSKL. Both those types were intended as the ultimate expression of a Mercedes-Benz sports car.

Decoding the SSKL, K for Kurz meant that the chassis had been shortened yet again. Mercedes cut the car from a wheelbase of 134 inches to just 116 inches. L stood for Leight or Lightweight, meaning that the vehicle had been extensively lightened. Both cars were shorter than the SS, and usually ran with stark, open two-seater sports bodies with exposed spare wheels bolted on the tail. The stunningly quick Type-SSK was so esoteric and specialized that only 33 were ever built.

As far as the extraordinary SSKL model was concerned, it was Hans Nibel who was given most of the credit for its evolution. He found two ways of making this true works race car: by increasing the engine's power output yet again, and lightening the chassis.

Since the engine’s displacement could not be stretched any further, Nibel’s team had to resort to the only obvious improvement: to urge more fuel/air through the power unit to liberate more power. This was done by working out how to evolve, and fit, a physically larger supercharger. This imposing new supercharger was the very aptly-named “Elephant” blower; the largest of the entire family of superchargers ever mated to this famous engine. This device, allied with changes to camshaft and other parts, generated at least 300 horsepower in extremis, although it was as a naturally aspirated 170-horsepower machine that the SSKL was used much of the time. 

The engine changes were not obvious unless an observer knew all about the different sizes of supercharger used by Mercedes-Benz. However, the alterations to the chassis were certainly well-known. To reduce weight as much as possible, Nibel resorted to the age-old method of drilling as many  holes as possible into every significant chassis member of the hand built machine. Though not an elegant solution, it worked.

It was now eight years since the original engine had been fired up. The Great Depression had hit Mercedes-Benz very hard, and the firm was now set on developing newer, smaller, and more economical machines to face the 1930s. Although there would still be a place for super-fast, super-costly cars at the head of the company’s range, these new cars would carry a new range of engines. The 370 - 540 series was on the horizon. 

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