Mercedes 120 hp racing car, 1906

Mercedes 120 hp racing car, 1906

Wilhelm Maybach, chief designer at Daimler-Motoren-Gesellschaft (DMG) and dubbed the "king of designers" in the press, had big plans for the 1906 motorsport season. With the help of the first six-cylinder racing engine to be developed by DMG, he wanted to put the moderate successes of the previous years behind him and finally decommission the four-cylinder engine that had been in use since 1903.

In an interview with the "Allgemeine Automobil-Zeitung" in the issue of 3 December 1905, Maybach had already praised the advantages of the six-cylinder engine in a racing car: "Only in one case, as already mentioned earlier, can I see the justification for the six-cylinder engine: if the driver wants to advance quickly, if he needs to keep his hands on the steering tiller, if he doesn't have time to change gear, or if a wrong manoeuvre with the speed lever can cost him precious seconds, then the six-cylinder, in which the play with the throttle and pre-ignition allows any variation in speed, has its full justification. You know what I'm referring to: the racing car. The most variable engine is the best for such purposes. The designer must make operation easier for the racing driver in every respect: he has to do everything he can to create a car that will get to the finish line in the shortest possible time."

The ultra-modern engine envisaged by Maybach for the new racing car bore a certain conceptual relationship to a 300 hp/221 kW marine engine that Maybach had been in charge of designing for the Russian Navy four years earlier. He was supported in this work by the talented Russian-born designer Boris Loutzky, who had studied in Munich and had made a name for himself in the industry since the turn of the century.

The six-cylinder was characterised on the one hand by the individual vertical steel cylinders and on the other by the complex casting of the cylinder head and the six cooling jackets, which were then welded together with the cylinders to form a single unit. Maybach also broke new ground in terms of valve control. Instead of the IOE control used in the previous four-cylinder engine, which was easy to repair but inefficient in terms of power output, Maybach provided overhead intake and exhaust valves housed in separate chambers on either side of the cylinder head and actuated by an overhead camshaft (OHC). For its part, the camshaft was driven by a vertical shaft at the front end of the engine, which also set the water pump, radiator fan and ignition magnetos in motion.

With bore/stroke dimensions of 140 x 120 mm, Maybach remained true to an oversquare design. As with the previous four-cylinder, this limited the overall height of the engine and ensured a certain liveliness despite the impressive total displacement of 11.1 litres, without allowing the piston speeds to rise into uncontrollable regions. The long crankshaft was mounted on seven bearings to prevent destructive torsional vibrations. The peak output of the six-cylinder engine was 120 hp/88 kW at 1500 rpm, while the continuous output was 106 hp/78 kW at 1400 rpm. Maybach's endeavours to keep the masses moved by the valve control system as small as possible had made this unprecedented speed level possible.

Unfortunately, a controversy arose within DMG during the design phase over the technical concept to be adopted for the new racing engine. Maybach's design was criticised above all by Maybach's fellow board members at DMG, above all Gottlieb Daimler's son Paul, who had left the Austrian subsidiary and had been working at the main plant in Untertürkheim again since 1905. Remarkably, this time Emil Jellinek, who was generally very fond of modern technology, was also among Maybach's critics. In particular, the entire design of the cylinder head, including the valve train and the high-voltage dual ignition, was considered overly progressive and more conservative technical solutions were favoured instead. 

The six-cylinder engine that Paul Daimler had designed as an alternative was compatible with these. The 12.9-litre engine had a square bore/stroke ratio of 140 x 140 mm, an unusually complicated IOE valve arrangement, a side-mounted camshaft with gear-driven centre drive, only four crankshaft bearings and still the outdated touch-spark ignition.

Maybach's racing car design was remarkable not only because of its engine; the chassis, too, featured innovative detailed solutions. The longitudinal frame members were cranked over the front axle - a first for Mercedes, the leaf springs were flatter and the radiator was lower, making the new racing car overall unusually low. The tank in the rear now had a flattened silhouette instead of the previous circular cross-section, which made it easier to accommodate the spare wheels. At 2690 mm, the wheelbase of the six-cylinder racing car corresponded to the dimensions of the 90 hp racing car from 1903.

In order to settle the internal disputes over the engine issue and to obtain a proper basis for decision-making, the DMG management decided to build three cars with engines based on Maybach's design and three with engines based on Daimler's plans. How many vehicles were actually built can no longer be clearly determined today on the basis of the available sources, but apparently two or three cars were built according to Maybach's concept and one or two according to Daimler's design. What is certain is that one of the 120 hp racing cars with a Maybach engine was present at the renowned "Circuit des Ardennes", the Ardennes race near the Belgian town of Bastogne, in mid-August 1906 and should probably have started, but was then put out of action in the run-up to the event due to a crack in the cylinder head. After a test drive as a passenger of Camille Jenatzy, the correspondent of the "Allgemeine Automobil-Zeitung Berlin" conveyed his enthusiasm in the 17 August issue: "Firstly, I joined Jenatzy for a very interesting test drive around the circuit in the racing car and at speed, which was fantastic. The diable rouge is a driver par excellence and I have repeatedly admired his skill on the bends [...] Incidentally, our Mercedes are running very well and the new demountable rims, which Continental brought out this time, have proved their worth in the tests. With the help of the new jack, the bottles of compressed air and the demountable rim, the time required to mount the rear wheels has been reduced to 2 minutes." The fact that this test drive was carried out with a six-cylinder racing car with a Maybach engine is shown in the photo reproduced in the article, which shows the vehicle with an open bonnet and the characteristic large valves of Maybach's six-cylinder engine.

The Mercedes four-cylinder racing cars that took part in the race instead of the six-cylinder version only finished in a disappointing 9th and 10th place under Otto Salzer and Camille Jenatzy, despite the removable rims.

To this day, there is no clear evidence that any of the six-cylinder racing cars, whether with a Maybach or a Daimler engine, ever competed in motorsport. One of the Mercedes six-cylinder racing cars equipped with a Maybach engine is now part of Mercedes-Benz Classic's own vehicle collection. Also preserved there is a separate engine built to the plans of Paul Daimler.

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