Restricting the displacement required a significant increase in engine speeds to between 3000 and 3500 rpm. In view of DMG’s experience with critical vibrations in the aircraft engines that had been used in 1913, the engine designers under Paul Daimler decided on a new concept. For the first time, steel cylinders threaded into the cylinder head with welded-on water jackets for each cylinder were used, a design that was to remain characteristic of Mercedes-Benz racing engines for decades to come. This meant that each cylinder received an adequate supply of coolant even in the most critical areas – the cylinder hotspots. The cylinder/cylinder head unit was bolted to the two-section aluminium crankcase.
Departing from previous cylinder head designs, the engineers employed a four-valve system in the 4.5-litre racing engine – an absolute first at DMG. The overhead valves in a V-configuration with an angle of 60 degrees were controlled by an overhead camshaft. This had three cams per cylinder, as the two intake valves were operated via a forked roller-type rocker arm, but the two exhaust valves by one forked roller-type rocker arm each. For vibration reduction, the five-bearing camshaft was driven from the rear end of the crankshaft by a vertical shaft. The same applied to the drive for the oil pumps and ignition magnets, which was also located at the end of the five-bearing crankshaft, though in this case a transversely arranged pinion shaft was used.
The pistons of the cars driven by works drivers in the 1914 Grand Prix were still of cast-iron, although attention was already turning to aluminium pistons. Although test-bed runs with the aluminium pistons had been completed successfully, most drivers still opted for cast-iron pistons. The car of the Belgian driver Theodor Pilette had aluminium pistons. Engines were only equipped exclusively with aluminium pistons in 1922, when DMG was preparing the vehicles for the Targa Florio race of that year. These lighter pistons allowed the maximum engine speed to be increased once again from 3200 to 3600 rpm.
To exclude every possible risk, the designers in Untertürkheim placed a particular emphasis on engine lubrication. The crankshaft was supplied with oil by two adjacent oil pumps, which were likewise located at the end of the crankshaft to minimise vibrations. Both pumps were configured so that they drew oil from the crankcase while also continuously feeding fresh oil into the circuit from a separate tank. A separate oil circuit operated by the driver via a foot-pump was responsible for lubricating the cylinder walls, camshaft and rocker arms. This enormous flow of oil made a commensurate ignition system necessary: three special Eisenmann spark plugs were fitted to ensure optimal ignition of the mixture. Two were on the intake side, one on the exhaust side. These spark plugs featured a centre electrode of Böhler-Rapid high-speed steel and two side electrodes of platinum.
The newly designed engine proved to be a resounding success – taking the first three places speaks for itself. During the First World War this engine received a further, unintended accolade. On 15 July 1914, the winning car was made available to the British Mercedes distributor Milnes Daimler Ltd for display purposes. Following the outbreak of the First World War the racing car was confiscated, and served as the technical model for the Rolls-Royce Hawk aircraft engine, while the valve assembly was adopted for his first motor engine by William Owen Bentley.
Until the end of the 1920s the engine was also used successfully in Mercedes racing cars: in 1922, Count Giulio Masetti, an Italian private driver, took overall victory in the Targa Florio in the redesigned Mercedes Grand Prix racing car, now painted in the Italian racing colour of red. In 1924, Count Giovanni Bonmartini won the hill-climbing race at Merluzza, near Rome, in a Mercedes works vehicle, while Count Doenico Antonelli took second place in Masetti’s car. That same year, 1924, also saw the introduction of a completely new combination: at the instigation of the drivers, the output of the engine that had been tried and tested over a period of ten years was increased by adding a compressor and installed in the chassis of the new Targa Florio racing car. The result was a car affectionately christened “Grandma” by the drivers, which went on to deliver top performance time and time again in hill-climbing races. The most notable successes were achieved by Rudolf Caracciola and especially Adolf Rosenberger. These demonstrated that this 4.5-litre racing engine designed in 1913/14 was so robustly conceived from the start that it could also cope without problem with considerably higher power levels.