Mercedes 115 hp Grand Prix racing car, 1914
The Grand Prix de France held at the beginning of August 1913 near Le Mans proved to be a commercial and sporting success despite the internal competition from the Grand Prix de l'A.C.F.: around 100,000 spectators lined the track, and the race itself left nothing to be desired. Nevertheless, this event remained the last Grand Prix de France under the aegis of the Automobile Club de l'Ouest (ACO). From 1914, the Grand Prix de l'A.C.F. once again became the actual and exclusive French Grand Prix.
In the run-up to the race, which was held on a circuit near Lyon, the organising Automobile Club de France (A.C.F.) once again reshuffled the cards in the highest category of motor racing. A revised set of technical regulations came into force which, in addition to the maximum weight carried over from the previous year, included a limit on the displacement for the first time: the total displacement was not permitted to exceed 4500 cc, whereby the combination of bore and stroke dimensions used was optional.
This first major technical restriction in the history of Grand Prix racing prompted all the manufacturers willing to take part to question the concepts and principles of engine design they had previously pursued. Almost none of the leading manufacturers in 1913 had a ready-to-use racing engine with such a small displacement, even though French manufacturers had the most experience with the small-volume racing cars of the Voiturette class.
In view of the technical level now achieved in the construction of racing engines, the challenge facing Paul Daimler and his team of engineers was enormous. Cylinder heads with four - sometimes even force-controlled - valves, which were actuated by one or two overhead camshafts depending on the engine concept, were the rule rather than the exception in Grand Prix racing in 1913.
The positive experiences with the four- and six-cylinder G 4 F and DF 80 aircraft engines used in Mercedes racing cars in 1913 prompted Daimler to continue using design principles from aircraft engine construction in the development of the new 4.5-litre racing engine.
The new engine with the designation M 93654 had the typical individual steel cylinders with welded-on cooling water jackets made of thin-walled steel, which were bolted to the two-part crankcase made of cast aluminium. This technology, found exclusively in the Mercedes cars in the starting line-up for the 1914 Grand Prix de l'A.C.F., guaranteed low weight combined with maximum cooling performance. Various estimates of how much lighter the Mercedes engines were compared to the engines of competing makes ranged from 30 to 50 percent.
With cylinder dimensions of 93 mm x 165 mm, the long-stroke four-cylinder engine also had four 43 mm valves per combustion chamber. The two intake valves were actuated by double rocker arms, while the exhaust valves were opened and closed by two single rocker arms. The latter was a design necessity at the time in order to be able to absorb the different expansion coefficients of the exhaust valves, which are subject to much higher temperature loads, and the intake valves, which operate at a cooler temperature. A single overhead camshaft, which was driven by the crankshaft at the rear end of the engine, i.e. the end facing the driver, via a vertical shaft with bevel gear, controlled the twelve rocker arms in total.
The maximum speeds, which had now reached the region of 3000 to 3500 rpm, made a more complex crankshaft bearing indispensable, especially as the two much larger-volume aircraft engines G 4 F and DF 80 had already shown that one of the most important tasks of the designers was to minimise the intensity of the torsional vibrations as far as possible. This was particularly true for a design with individual steel cylinders which, in contrast to a cast cylinder block, could not make any contribution to the internal rigidity of the crank assembly. The markedly long-stroke design and the resulting high piston speeds of over 17 m/s also made a five-bearing crankshaft a technical necessity.
The four-cylinder was lubricated by means of a complex pressurised system that had not just one, but three pump pistons: one supplied the crankshaft, connecting rod and piston pin with oil pressure, a second flushed the oil from the front of the oil pan to the suction snorkel of the oil pump at its rear end and a third pumped fresh oil into the system from a 15.1-litre oil container. If necessary, lubricant could also be pumped into the crankcase from a 3.8-litre oil container attached to the instrument panel, independently of the rest of the system. This tank also functioned as an additional reservoir if, depending on the situation, it became necessary to increase the oil supply to the cylinder barrels, the camshaft, the rocker arms, the steering gear or the universal joint on the drive shaft.
Basically, the combination of long-stroke design and welded steel cylinders, whose upper regions were insufficiently supplied with oil, created a lot of potential problems. This resulted, for example, in wear tracks on the pistons and cylinder walls, which could lead to piston seizure. The immediate consequence of this would be serious damage to the connecting rod and crankshaft. A look at the huge billows of oil smoke that the 4.5-litre Mercedes also emitted during the race suggests that the lubrication system of the four-cylinder engine was always filled with far more oil than necessary in order to achieve additional spray and atomisation effects, with the help of which the upper cylinder regions were to be supplied more effectively with lubricant.
To provide additional cooling for the valves, the parts of them that were outside the cylinder head were not covered by a housing cover, but left open to the airflow. At the time, this solution was primarily reserved for racing or aircraft engines because it could not always guarantee sufficient lubrication of the contact surfaces on rocker arms and at the upper end of the valve stems, and so lead sooner or later to damage. This was considered unproblematic insofar as appropriately designed aircraft engines in this era had to be completely overhauled after an operating time of 20 to 30 hours anyway. Given that a Grand Prix race lasts around seven hours, there was therefore a sufficient safety margin for the 4.5-litre Grand Prix engine.
In order to ensure that at least one or two spark plugs did not become oily and were able to do their job without impairment, given the excessive amounts of oil in the engine, each of the four cylinders was fitted with three special spark plugs; two were located on the intake side and the third on the exhaust side. As the engine was equipped with two magnetos, in the manner of an aircraft engine, a fourth spark plug could even have been supplied with power in an emergency.
With an engine output of 104 hp/76 kW at 3000 rpm, the 4.5-litre Mercedes was one of the most powerful cars on the grid at the Grand Prix, which was also reflected in the top speeds of over 160 km/h measured there.
Until 1913, all Mercedes racing cars had a chain drive to the rear axle. A chain drive of this nature kept the unsprung masses low, thereby reducing the always critical tyre wear and benefiting the overall handling. However, it was particularly suitable for use in cars with large-volume engines, whose high torque values placed enormous loads on the rear axles and drive shafts. The new, lightweight 4.5-litre engine with its significantly higher engine speed level produced far lower torques, which placed significantly less stress on both the chassis and all transmission components.
Nevertheless, the decision in favour of or against the chain drive remained controversial for a long time. Théodore Pilette, for example, the Belgian Mercedes representative involved in motor racing, who had come fifth in the final classification at the Indianapolis 500 miles in 1913 in a simple, cardan-driven Mercedes with a Knight slide-valve engine and had finished a very respectable third in the Grand Prix de France two months later, was a staunch advocate of the chain drive for the new Grand Prix car. In the end, however, Paul Daimler decided in favour of power transmission via a cardan shaft due to its lower weight.
As in the familiar Mercedes touring cars that had been produced since 1908, the drive shaft was connected to the transmission by a universal joint and ran through a torque tube that was firmly connected to the rigid rear axle. Power was transmitted by means of two half shafts, each of which was cast together with a crown gear as a special feature. The torque tube encasing the cardan shaft was in turn flexibly supported on a crossmember of the frame via a ball joint.
Paul Daimler broke new ground not only with the engine design, but also with the refined configuration of the chassis compared to the predecessor models of the 4.5-litre Grand Prix racing car. Although the basic concept of the pressed steel frame with two longitudinal members had not changed, the cleverly positioned reinforcing elements, for example on the steering gear and axle drive, as well as the now also offset longitudinal members on the rear axle mount, which ensured that the half-axles and cardan shaft were at exactly the same height under normal circumstances, resulted in a significant improvement in driving stability, especially at high speeds. The rigidity of the entire chassis construction was guaranteed by massive X-shaped struts between the longitudinal frame members, in conjunction with the extra-heavy aluminium crankcase of the engine. The latter was anchored to the frame by means of eight massive bolts in a four-point attachment and gave the entire front section tremendous stability.
The chassis elements used corresponded to the state of the art at the time: the front and rear axles remained rigid and were suspended on semi-elliptic springs. Friction shock absorbers were fitted all round to keep the inherent movement of the axles under control.
Unlike some of its competitors, DMG decided not to equip the new Grand Prix racing cars with additional front brakes. The inside shoe brakes on the rear wheels were still operated by hand levers and the outside band brake on the transmission output shaft was operated by a foot pedal. The brake drums of the rear inside shoe brakes were fitted with large radial cooling fins made of aluminium, which combined low weight and high cooling capacity.
Measures to reduce drag had been standard practice for Mercedes racing cars since 1908. The aluminium body of the new 4.5-litre Grand Prix racing cars had a markedly slim design and was literally hidden behind the pointed radiator, which faced into the wind. V-shaped wooden panels attached directly to the front axle contributed to the remarkable wind resistance of the cars. Aluminium wind deflectors mounted over the entire underside of the chassis served on the one hand to keep air turbulence to a minimum and on the other to protect important, low-lying components from stone chipping.
The new Mercedes racing car made its racing debut on 4 July at the A.C.F. Grand Prix on a 37.6 km triangular circuit near Lyon, which had to be completed 20 times. The track chosen by the A.C.F. offered spectators an attractive view in many places, and an exceptionally large section could be seen from the main grandstand at the start and finish. The course placed particularly high demands on drivers and vehicles, as the "Allgemeine Automobil-Zeitung" noted in its Vienna edition of 14 July 1914: "The circuit near Lyon was the most difficult terrain on which a Grand Prix has ever been held. There were altitude differences of more than 200 metres. The Lyon circuit has been called the 'track of 100 bends'."
The team from Untertürkheim had lined up with five racing cars, the maximum number permitted by the regulations per manufacturer, against seemingly overwhelming competition; in addition, a reserve car and numerous spare parts, including a vehicle frame and engine, had been brought along. 300,000 spectators witnessed an extremely exciting race in which Mercedes and Peugeot battled it out. Just over seven hours after the start, Christian Lautenschlager, Louis Wagner and Otto Salzer achieved a spectacular one-two-three victory. Max Sailer drove the fastest lap but, like Théodor Pilette, dropped out after a few laps. The basis for this first one-two-three victory in Grand Prix history was meticulous and carefully planned preparation. A sophisticated strategy - both in preparation and during the race - paved the way for the success that has secured Paul Daimler a place of honour in motorsport history to this day.
The outbreak of the First World War just three and a half weeks after the legendary victory prevented further racing activities, at least in Europe. Nevertheless, the era of the 1914 Grand Prix racing car was by no means over. In the July of that year, the American racing driver Ralph DePalma, who had already achieved significant successes with his Mercedes 37/90 hp in 1911 and 1912, acquired the car in which Louis Wagner had finished second in the Grand Prix, and went on to take numerous racing victories in the USA between August 1914 and 1917. His most spectacular success was undoubtedly the win in the 500 miles of Indianapolis on 31 May 1915.
After the end of the war, the 4.5-litre car was also used once more in some races in Europe. Count Giulio Masetti was particularly successful, acquiring the car driven by Otto Salzer in 1921 and winning several races in Italy in 1921 and 1922, including the Italian Grand Prix held near Brescia in September 1921 and the Targa Florio in April 1922. The works team was also represented at this event with two other Grand Prix cars, but they were fighting a losing battle against the local Count Masetti. Otto Salzer drove the car in which Pilette had retired from the Grand Prix, and Christian Lautenschlager drove a car that DMG had built from individual parts in 1919. Like Masetti's car, and as was by then common practice, the two works cars also had brakes on the front wheels, as well as a higher and therefore more powerful radiator, and a body tailored to it.
In 1924, the car driven by Lautenschlager was once more deployed in Italy: as a support and training vehicle at the Targa Florio, which was contested by the new 2-litre racing cars with compressor. On the way there, Alfred Neubauer took the car to the outskirts of Rome, where it won the "Corsa della Merluzza" hill climb in a new record time on 13 April with Count Giovanni Bonmartini at the wheel.
The outstanding qualities of DMG's first four-valve engine were not only exploited in racing. After the outbreak of war, the engine from Lautenschlager's winning car, which was on display in the Mercedes showroom in London, was sent to Rolls-Royce, where it was tested and dismantled. The knowledge gained in the process was directly incorporated into the British manufacturer's own designs. For example, all Rolls-Royce aircraft engines from the First World War were conceptually influenced by the Mercedes Grand Prix engine.
In 1924, one of these Mercedes Grand Prix engines was even fitted with a compressor and installed in a Targa Florio racing car of the latest design. Otto Salzer christened the car "Grandmother" and drove it in sprint and hill climb races, including the Semmering Race in September 1924. Two years later, the car, with an engine that was now more than twelve years old, raced again at the Semmering and took a win there, this time with Rudolf Caracciola at the wheel. The car was then taken over by Alfred Rosenberger, who won the Klausen Pass race in record time in August 1927 and continued driving the car with great success until 1930. This car later came into private hands and was finally scrapped in 1937. Three examples of the Mercedes Grand Prix racing car from 1914 still exist today: Christian Lautenschlager's winning car and the reserve car that was not used, which had been taken to Lyon in 1914, are in the hands of American collectors, while the car that Christian Lautenschlager drove in the 1922 Targa Florio is preserved in Mercedes-Benz Classic's own vehicle collection.