Mercedes 1.5-litre racing car, 1922

Mercedes 1.5-litre racing car, 1922

The boycott of major racing events that had been contractually agreed by the major European car manufacturers, including the Daimler-Motoren-Gesellschaft (DMG), in the wake of the Grand Prix de l'A.C.F. in 1908, had given an enormous boost to the previously little heeded category of small-volume racing cars known as the Voiturette class. New brands such as Bugatti, along with innovative technical solutions for drivetrains with a small displacement, had revitalised the scene and, by the outbreak of the First World War, ensured that the performance gap between the Voiturette vehicles and the big names had been significantly reduced during the absence of the latter from motor racing.

Following the war-related suspension of all racing activities in Europe and a period of recovery and reorientation following the conclusion of peace in 1918, the manufacturers turned their attention back to the possibilities of an involvement in motor racing at the beginning of the 1920s. The aim was not only to advance technical development in automotive engineering, but also to demonstrate the quality of the individual products to the public.

Especially in England, Italy and France, events in which Voiturette racing cars took part had become very popular. It was therefore only logical that DMG, towards the end of 1921, should also consider developing such a vehicle, taking into account its own export interests. The 6/20 hp series model, which made its debut at the German Motor Show in Berlin in September as DMG's first new car development after the First World War, already provided a suitable technical basis.

The 6/20 hp and its sister model the 10/35 hp, presented at the same time, featured a ground-breaking innovation that was to bring DMG and its products worldwide fame: the compressor, initiated by Paul Daimler and originating from aircraft engine development. Both the 1.6-litre engine of the series model, initially called 6/20 hp but renamed 6/25 hp when production began at the end of 1922, and the 2.6-litre engine of the 10/35 hp model, which became the 10/40 hp model, were highly sophisticated in design and featured an overhead camshaft driven by a vertical shaft.

As the technical regulations for the Voiturette class stipulated a displacement limit of 1500 cc, DMG decided not simply to reduce the displacement of the 1.6-litre output engine for racing use, but to thoroughly redesign it in order to exploit the potential of the design in terms of optimum power output. At the same time, the engine was given the new designation M 65134 in line with the nomenclature system of the time. In addition to a change in the bore/stroke ratio from 68 x 108 mm to 65 x 113 mm and a resulting total displacement of 1499.87 cc, the centrepiece of the further development was a new cylinder head.

With two overhead camshafts, which operated two intake and exhaust valves per cylinder at an acute angle to each other via bucket tappets, and a centrally arranged spark plug, the design embodied high-performance engine construction at its finest. In addition, the DOHC design necessitated further measures on the vertical-shaft drive. Since two camshafts now had to be driven instead of one, two short transversal shafts with additional bevel gears were used to set both camshafts in rotation.

The compressor, a considerably enlarged Roots rotary blower compared to that used in the 1.6-litre series engine, was not driven by the flywheel but from the front end of the crankshaft and was installed vertically. Voluminous pressure lines transported the compressed intake air to the pressure-tight individual carburettor, a DMG in-house development. When the driver depressed the accelerator pedal, he set the compressor in motion via an engaging cone clutch.

The information available today on the performance of the 1.5-litre racing engine varies widely. In 1922, the factory indicated an output of 40 hp/29 kW without compressor and of 65 hp/48 kW at 4000 rpm with compressor. The literature states 45 hp/33 kW at 4300 rpm without compressor and 67 hp/49 kW at 4500 rpm with compressor, while test stand measurements on record in 1948 apparently showed significantly higher figures: 54 hp/40 kW without and 79 hp/58 kW at 4500 rpm with compressor. 

DMG produced a total of 24 units of this engine, of which three were installed in racing boats and all the rest used in cars. Regardless of how powerful the four-cylinder engine actually was, the basic technical concept realised here for the first time was so modern and forward-looking that it served as a model for all subsequent Mercedes and Mercedes-Benz racing engines until the 1950s.

Two of the 1.5-litre compressor racing cars took part in their first race for the works team in April 1922 at the Targa Florio in Sicily. Both had a wheelbase of 2740 mm and a track width of 1200 mm; the cars were also equipped with four-wheel brakes. The Mercedes racing team, which had travelled with a large entourage, also included two modified Grand Prix racing cars from 1914 and two current 28/95 hp racing touring cars, one of which was also equipped with a compressor engine. 

Unfortunately, the race on the extremely challenging Madonie circuit did not go quite as hoped for the works team from Untertürkheim. The fastest Mercedes works driver was Max Sailer in 6th place with the compressor model 28/95 hp. Behind Sailer, Christian Werner took 8th place in the second 28/95 hp. Christian Lautenschlager and Otto Salzer, competing in the 1914 Grand Prix cars, finished in 10th and 13th place respectively. Of the two completely newly developed 1.5-litre racing cars with twin-camshaft supercharged engines, only Paul Scheef's car managed to complete the full race distance of 432 km. Scheef finished twentieth in the final classification. The Italian Fernando Minoia, who was driving the second of the small compressor vehicles, gave up for unknown reasons. The "Allgemeine Automobil-Zeitung" of 28 May 1922 stated in an article written by Max Sailer that this was "particularly annoying because there was nothing wrong with the car; it was turned on and completed the journey from the start all the way to Stuttgart without any problems at all."

Although the race was won by a Mercedes, it was a privately registered 4.5-litre Grand Prix racing car from 1914, driven by Conte Giulio Masetti and painted in the red racing colour reserved for Italy.

After the disappointing debut of the highly developed 1.5-litre supercharged cars in Sicily, their racing career was not yet over. Apart from tests with aerodynamically optimised bodies, for which one of the two Targa Florio cars was used, the two cars were used in various motorsport events in 1923 and 1924. Rudolf Caracciola achieved his first racing victories in a Mercedes with one of these two cars.

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