Mercedes 2-litre Indianapolis racing car, 1923
New engine regulations had already come into force for the 1922 motor racing season, which – whether with or without forced induction – stipulated a displacement limit of 2000 cc instead of the previous 3000 cc. As German and Austrian car manufacturers were still banned from taking part in the French Grand Prix and other major international races in France and Belgium after the end of the First World War, Daimler-Motoren-Gesellschaft (DMG) turned its attention to the racing scene in the USA and Italy – countries where German makes were welcome at the start of prestigious racing events.
In 1922, DMG started the development of a new 2-litre racing engine. This was not least because the organisers of the Indianapolis 500-mile race also had decided to adopt the European engine formula for the biggest racing spectacle of the year from 1923 – a decision that was also aimed at luring further manufacturers from the old continent to come overseas.
The new design was modelled on the ultra-modern 1.5 and 2.6-litre four-cylinder vertical-shaft engines with compressor, which had recently ushered in a new era of engine development at DMG. With cylinder dimensions of 70 x 129 mm, the 2-litre engine was clearly undersquare and, like the 2.6-litre production engine, still had a triple friction-bearing crankshaft in the early phase of testing. After the first five test units, the company switched to a built-up Hirth crankshaft, which rested in three roller bearings - incidentally the first DMG engine to follow this design.
The design of the cylinder head and valve train was largely based on the technologies used in the 1.5-litre engine. The new 2-litre racing engine therefore had two overhead camshafts, which actuated two intake and two exhaust valves per cylinder via tappets. Compared to the older 1.5-litre engine, however, the positioning of the intake and exhaust valves was changed.
Another innovation that was to set the style for the design of Mercedes-Benz racing engines for decades to come was the welding of the cylinder and cylinder head, which was carried out for the first time on the 2-litre racing engine. The main aim of this trick was to increase the reliability of the compressor engines, which were subjected to high working pressures. Due to their often still inadequate material quality, the cylinder-head gaskets of the time tended to burn out under such conditions.
According to expert automotive historians, the official power output data of 150 hp/110 kW at 4800 rpm with compressor are more a reflection of the engine's performance towards the end of its development in 1924. Estimates found in factory records from the 1940s and 1950s are probably more realistic. A maximum output of 110 hp/81 kW to 125 hp/92 kW at 4500 rpm with compressor is specified there.
While there were many new features when it came to the drivetrain, the chassis structure reflected common practice. The backbone was formed by two U-shaped longitudinal members made of pressed steel, which were braced together in several places and carried a rigid axle at the front and rear, suspended on semi-elliptic springs and kept under control by friction shock absorbers. Where the leaf springs were attached to the rear axle, the longitudinal rails were cranked upwards to achieve a low car body. They were also bent inwards at their rear end. Deceleration was delivered by inside shoe brakes all round.
As the new regulations for the 1923 Indianapolis 500-mile race now for the first time did not stipulate that a co-driver acting as a mechanic had to be present, DMG, like many of its fellow competing manufacturers, could have mounted a single-seater racing car body on the chassis. For safety reasons, however, the decision was made in favour of a two-seater body, which was very low but less slender and had a boat-like tail that tapered to a point. Presumably in order to improve wind resistance on the high-speed Indianapolis circuit, tests were also carried out in advance with discs fitted to cover the wire-spoke rims, but these were not used in the end.
The results achieved by the Mercedes team in the race held on 30 May 1923 were respectable. Given the tricky handling of the car, which showed explosive power delivery when the Roots compressor kicked in, and the unfamiliar conditions on a track that proved particularly slippery in the adverse weather, Max Sailer's eighth place and Christian Werner's 11th place against the strong local competition can certainly be regarded as a success. The third Mercedes works driver, Christian Lautenschlager, had already retired after an accident on the 15th of a total of 200 laps to be completed. After all, in the overall standings they had outperformed manufacturers such as Duesenberg, Packard and Bugatti, the only European competitor in the starting field.
Shortly after the end of the USA expedition, the 2-litre racing cars achieved impressive victories on the old continent. Otto Salzer won the 6-kilometre Solitude Hill Climb near Stuttgart on 17 June 1923 with the fastest time of the day and an average speed of 96.9 km/h. In contrast to the vehicles used in Indianapolis, which were painted white, Salzer's winning car had a shiny silver body modified in details. In this colour scheme, but with further modifications to individual details, the car was driven by Otto Merz to second place overall in the Zbraslav–Jílovišt? (Königsaal–Jilowischt) Hill Climb held near Prague in April 1924. The overall winner was once again Otto Salzer, who started the race with an aerodynamically optimised version. This double victory marked the last outing for the Indianapolis racing car. Just one week later, a fundamentally revised version of the 2-litre supercharged racing car was fielded at the Targa Florio.