Mercedes 37/90 hp racing car, 1911
The French car manufacturers had been deeply shocked by their defeat at the Grand Prix de l'A.C.F. - so much so that, almost to a man, they had immediately wanted to withdraw from motor racing. In the meantime, however, new facts had been created: at a conference organised by the A.I.A.C.R. (Association Internationale des Automobile Clubs Reconnus), the international automobile association of the time, in the Belgian seaside resort of Ostend in mid-October 1908, the technical regulations for the next Grand Prix to be held in July 1909 on a newly selected circuit near Anjou in north-west France, had already been agreed. The key points of the new regulations were a reduction in the prescribed minimum weight to 900 kg and a reduction in the maximum bore size of the engines from 155 mm to 130 mm.
Not least because of the exorbitantly high entry fees demanded by the Automobile Club de France (A.C.F.) for the Grand Prix it organised, two Belgian and one Italian manufacturer as well as the Daimler-Motoren-Gesellschaft (DMG) and Benz & Cie. had now contractually agreed to stay away from all important races for the time being, along with nine French manufacturers. Such a moratorium was probably not at all inconvenient for DMG and Benz, as the memory of the 1908 triumph remained alive among the interested public. Moreover, the contract did not prohibit any manufacturer from continuing to equip and support interested private drivers with high-calibre racing cars.
As a result of the manufacturers' boycott, the A.C.F. was ultimately forced to cancel the Grand Prix for 1909. In the following year, the plans also failed due to the unwillingness of the contractual partners to compete in major races with works vehicles again. DMG also suspended all activities directly related to international racing in 1909 and 1910. Above all, no new highly specialised competition vehicles were developed, for example for customers in the USA, where racing was flourishing and was not affected by the boycott of the European manufacturers.
This situation did not change until 1911, when there was once again some movement on the scene. Based on the new top model in the passenger car range, the Mercedes 37/90 hp, designed under the aegis of Paul Daimler, a racing version was built in Untertürkheim to be sold to private drivers. The engine of the new car, a long-stroke four-cylinder with a displacement of just under 9.6 litres, had technical features that were reminiscent of Wilhelm Maybach's legendary six-cylinder engine of 1906, which had become the subject of internal dispute, but also evoked Daimler's own six-cylinder design, which he had deliberately launched as a counterpoint to Maybach's markedly progressive concept.
The four-cylinder engine presented itself as an interesting combination of innovative and rather conservative technical solutions. The unusual three-valve cylinder head with one intake and two exhaust valves, which were now all arranged in an overhead configuration, was extremely progressive. Less sophisticated, but absolutely appropriate for the engine of a sporty touring car, was the control of the three valves. Daimler used two side-mounted camshafts here, which opened and closed the valves by means of pushrods and rocker arms. In a similar approach to that used in Daimler's six-cylinder engine, the power to drive the camshafts was not taken from the front or rear end of the crankshaft as was conventional, but from the centre, i.e. in the case of the four-cylinder engine, from between the two pairs of cast cylinders. The exhaust camshaft on the left-hand side of the engine was rotated by the crankshaft using a gearwheel and in turn drove the intake camshaft on the right-hand side of the engine - also with the help of gears.
Daimler now also turned to state-of-the-art solutions for the technical periphery of the four-cylinder engine and equipped it with a dual ignition system, which was supplied with power by two magnetos. Whether and to what extent further modifications were made to the standard engine to make it suitable for racing is unfortunately not documented in the available sources, nor is there any reliable information on the performance of such a racing engine.
The chassis of the victorious Mercedes Grand Prix cars last used by the factory in 1908 appeared to Daimler to be suitable for equipping with the new racing engine. In an effort to reduce air resistance, the radiator was given a forward-tapered, flow-optimised cladding.
Measured against the limited effort that had been made in Untertürkheim to produce a competitive vehicle for private drivers, the success of the 37/90 hp racing cars was nothing short of sensational, especially in the USA. In the hands of Ralph DePalma and the young Spencer Wishart, the former Mercedes Grand Prix racing cars with their new engines achieved results that popularised their appeal immensely. At the end of November 1911, Ralph DePalma succeeded in winning the prestigious William K. Vanderbilt Cup in Savannah/Georgia, setting the fastest lap and finishing second, just behind the winner, ahead of his brand colleague Wishart. In the American Grand Prize held three days later, also in Savannah, he took third place with his grey-painted 37/90 hp, which he had christened the "Grey Ghost".
The two US drivers also caused a sensation with their Mercedes racing cars in the 1912 racing season. The 500 miles of Indianapolis, held for the second time on 30 May, ended in disappointment for Wishart and especially for DePalma. With a commanding lead of five laps, DePalma's 37/90 hp, which this time had started without its radiator grille, suffered a broken connecting rod three laps before the end and finally came to a halt just one kilometre from the finish. Cheered on by 80,000 spectators, DePalma and his co-driver pushed the "Grey Ghost" across the finish line to take 11th place and thus secure prize money of 1100 US dollars.
The rest of the season was more successful: at the end of August, DePalma won the Elgin National Trophy in Elgin, Illinois, winning the race with a new record average speed of 112.7 kilometres per hour. His winning streak continued at the beginning of October: in the race for the William K. Vanderbilt Cup, he crossed the finish line first in the "Grey Ghost", followed by Spencer Wishart in third place, also in a Mercedes 37/90 hp. His luck ran out at the American Grand Prize, which was held three days later on the same track: while trying to overtake the leading Fiat of Caleb Bragg, he touched the rear wheel of the latter and went off the track. This resulted in him being hospitalised for nine weeks, but did not prevent him from winning the American Automobile Association's National Championship in the end.
Ten months later, in August 1913, a 37/90 hp racing car was used once again at the Grand Prix de France, which was held on the triangular circuit near Le Mans. With Belgian Léon Elskamp at the wheel, it finished in seventh place.