Mercedes 2-litre "Targa Florio" racing car, 1924
Following the successful introduction of the new 2-litre four-cylinder racing engine with supercharger in the spring of 1923, Ferdinand Porsche, who had recently moved from Austro Daimler to DMG in Untertürkheim as Technical Director and member of the Board of Management, initially took over responsibility for this engine. Without changing its basic design, he revised the engine extensively in order to further increase power output and reliability.
The main innovations were a reduction in compression while at the same time enlarging the Roots compressor, and making use of internally cooled exhaust valves for the first time. While the first measure led to an increase in engine performance, the second resulted in a reduced temperature load on the two exhaust valves per cylinder by filling the hollow-bored valve stems with mercury.
The peak power output of the racing engine, which, like its predecessor, had two overhead camshafts with a vertical-shaft drive and a total of 16 valves, is reported in different sources. They range from 67.5 hp/49.7 kW without compressor and 126 hp/93 kW with compressor to 150 hp/110 kW with compressor by the time development work ended. A maximum engine speed of 4500 rpm or 4800 rpm is specified.
For the Targa Florio, which took place in Sicily at the end of April 1924 and where German car manufacturers were welcome despite a ban on starting that was still in force in some cases as a result of the war, the revised engine was installed in a chassis that was based on the chassis of the previous year's Indianapolis racing car. According to contemporary factory drawings, it sported a track width widened from 1340 mm to 1400 mm at the front and rear and was thus only marginally modified. At the rear, the frame side members did not merge as in the Indianapolis racing car, but continued to run parallel in order to accommodate the spare wheels, which were essential for use on country and mountain roads. A small windscreen in front of the driver sitting on the right was to protect the driver's face against being hit by stones in particular. Wings mounted all round served to protect against stone chipping – at least during the journey to the race and the subsequent return journey to the factory.
After the very varying experiences of the Targa Florio in previous years, DMG wanted to leave nothing to chance and completed an unusually extensive preparation programme. This included extensive test drives, which were carried out in Sicily in the January, and a measure that had already proved its worth during Conte Masetti's surprise victory in 1922 in one of the Mercedes 4.5-litre Grand Prix racing cars from 1914: the 2-litre racing cars intended for the starting line-up in Sicily were painted red, a racing colour that was actually reserved for Italian makes. This was a clever way of preventing overly fiery Sicilian racegoers from being tempted to actively obstruct white-painted, i.e. recognisably German vehicles in the race.
The considerable effort put in by DMG paid off. After a race lasting over six and a half hours, works driver Christian Werner secured victory at the Targa Florio in one of the red 2-litre racing cars. Christian Lautenschlager took 10th place in the same model of vehicle. Alfred Neubauer, a new member of the DMG racing team, finished in 15th place, more than an hour behind the winner.
Following their success in one of the most demanding and prestigious races in the world at the time, the 2-litre racing cars continued to be used and achieved a wealth of outstanding results.
Just three weeks after the Targa Florio, Otto Merz set the best time of the day in the Soltitude hill climb, setting a new track record of 103.4 km/h; second place went to Otto Salzer. The International Kilometre Race at Scheveningen at the end of June 1924 was similarly successful, with Dutch Mercedes importer Theo Wiemann setting the best time of the day in the 2-litre racing car. In mid-August, Otto Merz again set a new track record at the International Klausen Pass Race, while Otto Salzer took second place in the open class up to 3 litres displacement. At the Semmering race a month later, Targa Florio winner Wilhelm Werner was back in action: he set the best time of the day in the 2-litre racing car and set a new Semmering record.
At the same event in September 1924, a special one-off made its debut at the instigation of Otto Salzer. A 4.5-litre engine from the legendary Grand Prix racing car of 1914 additionally fitted with a supercharger was implanted into the proven chassis of the current 2-litre car. In its debut race at the Semmering, Otto Salzer set a class record for racing cars over 3 litres, but was 10 seconds behind the best time of his team-mate Christian Werner.
On 21 September, Otto Salzer achieved the best time of the day with the 2-litre racing car at the Ecce Homo Hill Climb in Czechoslovakia; in contrast, Conte Giulio Masetti and Karl Sailer's outing at the Gran Premio de San Sebastian ended six days later with a total failure. First Sailer and later also Masetti came off the track, causing serious damage to their racing cars.
In the following year, the Targa Florio racing car helped its drivers to further victories: In May, Otto Merz set a course record in the 223-kilometre "Rund um die Solitude" Race and set the best time of the day. At the end of June, Rudolf Caracciola, then still a junior driver in the Mercedes team, achieved the same success in the Teutoburg Forest Race. At the Bleichröder Race organised as part of the Robert-Batschari-Fahrt in July 1925, it was again Christian Werner who set the best time of the day with an average of 139 km/h. Subsequently, the 2-litre eight-cylinder car in its various versions was mainly used instead of the Targa Florio racing car in the very popular hill climb races of the time.