Benz 120 hp Grand Prix racing car, 1908
After the encouraging results achieved in 1907 with the 60 hp Targa Florio racing car, Benz & Cie. in Mannheim was aiming to become involved in the top categories of the most important racing events for the 1908 motorsport season. The focus was now on overall victories instead of class victories.
In order to be competitive at this level, a completely redesigned vehicle was needed. The Belgian Louis de Groulart would go on to design a slightly long-stroke four-cylinder engine at Benz which, unlike the racing engines of previous years, featured overhead intake and exhaust valves. De Groulart utilised the maximum bore size of 155 mm specified by the regulations and chose a stroke of 160 mm. The displacement of the engine was thus 12,076 cc and its peak output reached 120 hp/88 kW at 1500 rpm. De Groulart's design was characterised above all by its significantly reduced weight: the new racing engine was lighter than the engine of the Targa Florio racing car from the previous year, despite having twice the power. In addition to the 12-litre engine, de Groulart also designed a variant with a 40 mm longer stroke, which generated an output of 150 hp/110 kW from a displacement of 15.1 litres.
The large-volume four-cylinder engines were embedded in a state-of-the-art frame. Two pressed steel profiles with a U-shaped cross-section acted as longitudinal members. To ensure the necessary stability, these were connected to each other by numerous crossmembers. To keep the overall height and consequently the vehicle's centre of gravity as low as possible, the two longitudinal members above the rear axle were offset. The two rigid axles suspended on semi-elliptic springs were to be kept in check during racing by coil-spring shock absorbers mounted all round. The engine power was transmitted to the rear wheels via a 4-speed gearbox and chains on both sides.
The mechanical brake system of the racing car, which could reach speeds of up to 160 km/h, was limited in its effectiveness, as was customary at the time, and its operation required as much skill as sensitivity. The deceleration instruments comprised inside shoe brakes on the rear axle and outside band brakes on the intermediate shaft that transmitted the drive torque from the transmission to the front sprockets of the axle drive. A special feature was the design of the rear inside shoe brakes: each wheel had its own foot pedal, allowing the driver to vary the type and intensity of the braking effect - a potential advantage in hectic racing.
The first 120 hp Grand Prix racing car, completed in the spring of 1908, differed from the subsequent models in that the position of the driver and mechanic as well as the fuel tank was moved further back; in addition, the bonnet had 18 instead of the 16 ventilation slots of the later models.
After extensive test drives, Victor Hémery, the French star driver of the Benz racing team, took the 12-litre car to the starting line for the first time at the beginning of June in the 686-kilometre Petersburg-Moscow endurance race. The gruelling stage ended with a sensational triumph for Hémery, who beat the previous year's winning time by 51 minutes with a time of 8:30:48.
At the Grand Prix de l'A.C.F., the French Grand Prix, held at the beginning of July on a circuit in Dieppe in northern France, Hémery - who had contested the previous year's event, also in Dieppe, in a Mercedes - impressively demonstrated his fighting spirit. After almost five hours of racing, he was only 51 seconds behind the leading 140 hp Mercedes of Christian Lautenschlager in his Benz Grand Prix racing car. The Frenchman then became lucky in his misfortune: a stone that was thrown up smashed through the glass of his driving goggles, causing a splinter to enter his eye. After brief medical treatment, Hémery was able to resume the race, still in second place. Despite the handicap, he managed to maintain this position until the finish. Hémery's French team-mate at Benz, René Hanriot, and Fritz Erle completed the outstanding performance of the newly developed Grand Prix racing car with third and seventh place, respectively. Thanks to this cohesive team performance, Benz won the regularity classification. According to some sources, Erle was already racing in the Grand Prix in Dieppe with the 15.1-litre long-stroke engine; even if this cannot be conclusively clarified from today's perspective, it seems unlikely overall.
Another significant success for the Benz Grand Prix car was the Semmering hill climb that took place near Vienna, which was held for the tenth time in September 1908. Victor Hémery took third place in the Grand Prix race car classification behind the two Mercedes of Otto Salzer and Willy Pöge.