Directly derived from the K, the 1927 model S (Sport) had impressively low construction and looked as fast as it was. The engine was bored to 6.8 liters; the Roots blower was gear-driven and set to run at three times crankshaft speed. This boosted maximum power to 180 supercharged and made the SK a genuine 100-mph car. It also featured a new four-speed gearbox with very low numeric ratios (2.76:1 standard, 2.5:1 and 3.08:1 optional), and its light roadster body gave it a curb weight of only 2,867 pounds.
The racing impact of the S was tremendous. During its career it racked up 53 racing victories and 17 speed records, including a German national mark for passenger cars of 110.3 mph. It was expensive, of course, and thus uncommon: most estimates put the total at 149, all built in 1927-1928.
At the end of 1928, Porsche left Daimler-Benz for Steyr in Vienna, and in 1930 he set up his own engineering firm in Zuffenhausen, where he became involved in the Volkswagen project. Meanwhile, he was replaced at Daimler-Benz by his former assistant Hans Nibel, another brilliant technician. Nibel's credits included the great 200-bhp "Blitzen Benz" speed record car of 1910 and a host of fine touring cars in the early Twenties.
Porsche was still at the helm when an even more formidable sporting Mercedes went into production in late 1928: the SS (Super Sport), basically a lighter S (by about 66 pounds) with a more powerful, seven-liter engine. Its blower, providing eight psi boost, was shared with the S, but compression was raised and valves and ports were larger. Maximum supercharged horsepower now rose to 200, top speed to 115 mph, and 0-60 took less than 15 seconds. Such numbers seemed like fiction in the world of 1928, but they were valid enough.
The SS remained in production up to 1933, but very few were constructed after the end of 1929. Total production is estimated at only 109 cars. Next step was the yet-hairier SSK, a short-wheel-base derivative of the SS built alongside it in 1928. As with the 1926 Model K, the letter denoted kurz (short). Its chassis was lighter still at 2,680 pounds. In addition a bigger blower delivering 10 psi boost, gave the SSK engine more power. With the supercharger engaged it put out 225 bhp at 3,200 rpm, good for a sizzling 120-mph top speed under test conditions with perfectly tuned factory examples.
The SSK enjoyed a brilliant competition career. Caracciola scored its first victory at the Gabelbach hillclimb in 1928, then repeated Model S wins at Frieburg and Semmering. In 1930, he won the Irish Grand Prix in an SSK against a host of open-wheel racing cars.
On track or road the SSK was truly a supercar. Britain's The Motor published a test in June 1931 and said the results (0-90 in 45 seconds, top speed 103.2) fell short of expectations. Considering the state of the art in the early 1930s, the editors must have expected a great deal, for such performance was then unequalled by any other car in the world. The number of SSKs built is estimated at 31, all from 1928 to 1931.
On the next page, learn about the light-weight SSKL.