Mercedes-Benz Grand-Prix racing car W 154, 1939
After the almost total dominance of the W 154 in the 1938 racing season, which had brought Rudolf Caracciola his third European Championship title, the aim was to dominate the Grand Prix racing scene again in 1939 in a duel with the Auto Union Type Ds, which had clearly become stronger towards the end of the season. The subsequent outbreak of war did not immediately cast a shadow over the further technical development of the W 154; tests with a different compressor technology continued even into the spring of 1940.
In general, the intake side of the proven V12 engine was the focus of the designers for the races of 1939. Primarily, further potential for increasing performance was seen in the forced induction of the combustion mixture. Based on the realisation that a single, two-stage compressor requires considerably less drive power than two single-stage ones, a solution of this nature was developed in Untertürkheim together with a new upstream twin carburettor.
The improved efficiency of the two-stage compressor due to the omission of the second compressor resulted in increased peak power on the one hand, which rose by 5 to 15% depending on the specific engine specimen and rpm range, and varied between 450 hp/331 kW and 483 hp/355 kW at 7500 to 7800 rpm. On the other hand, the torque curve was flatter, so the power was available over a wider rev band. In addition, the overall engine speed level was somewhat reduced, which benefited the reliability of the M 154 engine. The crankshaft and especially the connecting rod bearings of the 3-litre V12 reacted sensitively as soon as the upper rev limit of about 8000 rpm was reached, let alone exceeded.
The two-stage compressor consisted of a large and a smaller Roots blower, arranged slightly offset in sequence and connected by a flat tube. The installation position of the single compressor was also new: it now lay horizontally in front of the front end of the engine. The two compressors used previously, on the other hand, had each been placed upright but slightly inclined in front of the cylinder banks.
An M 154 equipped with a two-stage compressor was used for the first time in the racing vehicles of Hermann Lang and Hans-Hugo Hartmann - a young talent in the Mercedes-Benz racing team - in the Eifel Race on the Nürburgring. The race, held on 21 May 1939, demonstrated the superiority of the new concept and promptly ended with Lang winning ahead of Tazio Nuvolari in the Auto Union Type D and two other W 154s of Caracciola and von Brauchitsch, still equipped with two single compressors.
In the battle to defend their title in the European Championship successfully, those in charge did not want to rely solely on the - albeit more powerful - 1938 engine. The company therefore pushed ahead with the development of a new evolutionary stage of the 3-litre V12, which did not offer any profound technical innovation, but eliminated certain design weaknesses of the power unit. The thoroughly revised engine was even given the new designation M 163.
It benefited from a wider crankcase that brought more stability, but was mainly characterised by numerous detail modifications that served to improve oil tightness. Until now, the high pressures occurring inside the engine had led to larger quantities of lubricant leaking out, which had resulted in astronomical oil consumption at times. To solve this problem, the fasteners of the valve covers and timing cases as well as the oil pan were modified. At the same time, a previously existing shaft that was supposed to drive a petrol direct injection system was removed - this revolutionary innovation was not yet ready for use in racing for the time being.
The new engine version made its début in the W 154, whose designation had remained unchanged, in the Belgian Grand Prix, which was held on the high-speed circuit of Spa-Francorchamps on 25 June 1939. Hermann Lang, whose car was equipped with an M 154 engine, nevertheless took the victory ahead of Hasse in an Auto Union and von Brauchitsch, whose W 154 had the more advanced power unit. The race ended tragically for Richard "Dick" Seaman, the second Mercedes-Benz driver, whose car had rolled onto the grid with an M 163 engine. He suffered a serious accident on lap 22 while in the lead and died of his injuries the night after the race.
In terms of peak power, the modified M 163 engines were by no means superior to the M 154 with two-stage compressor. Depending on the engine, peak values in the range between 417 hp/307 kW and 477 hp/351 kW at 7500 rpm are documented.
However, the further development of the W 154 for the 1939 racing season was not limited to the engines. Specific improvements were also made in the areas of chassis, suspension and aerodynamics. By using lightweight materials, especially on the chassis, it was possible to reduce the vehicle weight to 859 kg in accordance with the weighing procedure defined in the regulations, excluding fuel, coolant and driver, and thus come close to the minimum weight of 850 kg set by the regulations. The W 154 of the previous season had still weighed 981 kg under the same conditions.
A standardised solution was also found for the complex issue of the tank specification, which even with decreasing fuel in the tank hardly affected the driving behaviour any longer. A total capacity of 420 litres was chosen, of which 235 litres were allotted to the saddle tank located between the rear end of the engine and the driver, which had been established the previous year, and the remaining 185 litres to the rear tank. The decisive innovation, however, was that the two tanks now emptied in sync rather than consecutively – meaning that driving characteristics that depended on the respective fill level, which some drivers of the W 154 had complained about in the previous season, were essentially a thing of the past.
The newly dimensioned fuel tanks with smaller rear tank were one of the reasons why the exterior appearance of the W 154 of the 1939 season was also visibly different from that of the previous year's version. A second reason was a modified radiator arrangement. Extensive investigations had shown that the positioning of the combined water/oil cooler permitted neither an aerodynamically efficient flow nor fast heat dissipation. This resulted in a more forward installation position, which created a rounder shape at the front of the vehicle with a higher body silhouette. Overall, the Grand Prix car appeared stockier and not quite as low and even elegant as before.
The brake system was also significantly improved by the introduction of the innovative so-called turbo brake. Its cooling fins, arranged both radially and axially on the outside of the brake drum, resulted in particularly fast and efficient heat dissipation, which significantly increased the continuous load capacity of the entire brake system.
The 1939 motor racing season as a whole, including the races for the European Grand Prix Championship, suffered greatly from the dramatically worsening global political situation. While the Association Internationale des Automobile Clubs Reconnus (AIACR) - the automobile umbrella organisation that was also the international motorsport authority - had as in previous years announced the four Grand Prix races counting towards the European Championship before the start of the season, there were many race cancellations from August onwards, just before the outbreak of war, including the Italian Grand Prix, the Masaryk Grand Prix and the Donington Grand Prix.
Although the four races counting towards the European Championship, the Grands Prix of Belgium, France, Germany and Switzerland, were not affected, the points table was not completed by the AIACR, which ceased its work during the course of the year in view of the circumstances. As a result, no European Champion was officially crowned. Instead, the representatives of the Nazi regime took it upon themselves to grace Hermann Lang with a European Championship title. Although the Swabian had not achieved the highest points score in the four rounds of the European Championship according to the system practised so far, he was overall the most successful driver of the entire season. A new points system, not unlike the model used in the later World Automobile Championship, would have seen Hermann Lang in the lead, but was not introduced - just as in the end no official points table was published by the AIACR at all.
In addition to starts in the four championship races at Spa-Francorchamps, Reims, the Nürburgring and the Bremgarten Circuit at the beginning of the season, the Mercedes-Benz racing team's race schedule also included participation in the Grand Prix de Pau and the Eifel Race. The season ended on 3 September with the Belgrade Grand Prix, which was held despite the war that had broken out two days earlier.
In addition to the Grand Prix version of the W 154, a variant specifically developed for hillclimb races was also used in 1939 and was available for the Vienna Höhenstrassenrennen (High Road Race) in June and the Hillclimb Grand Prix on the Grossglockner high Alpine road in August. It helped Hermann Lang to win the Vienna Höhenstrassenrennen, but at the Grossglockner the more powerful W 125 joined the starting line-up instead.
As in the previous year, the race held on a narrow city street circuit in the French Pyrenean town of Pau marked the start of the Grand Prix season. The Untertürkheim racing team rolled up to the start almost at full strength with three W 154s for Caracciola, von Brauchitsch and Lang, while their fiercest rival, Auto Union with its mid-engined Type D cars, skipped this race, which took place as early as on 2 April.
The result of the more than 100-lap Grand Prix de Pau quite clearly reflected the balance of power in the starting field. With a lead of two laps over the third-placed Talbot, Hermann Lang and Manfred von Brauchitsch achieved a highly convincing one-two win for Mercedes-Benz. Neither the twisty course nor the W 154, equipped as before with two single-stage compressors, made it possible to get an idea of the true performance of the 3-litre Formula racing car that had been further developed for the current season.
The Eifel Race held seven weeks later, on 21 May 1939, on the Nürburgring turned into a first, almost humiliating demonstration of the dominance of the two German racing teams. Nine of the 13 cars on the grid belonged to the Mercedes-Benz and Auto Union works teams.
Hermann Lang crossed the finish line after ten laps as the winner. Tazio Nuvolari in the Auto Union Type D followed in second place about 11 seconds behind. Third and fourth places went to Caracciola and von Brauchitsch. Richard "Dick" Seaman had to abandon his W 154 after a failed start with a burnt clutch.
The next race and first championship round was the Belgian Grand Prix in Spa-Francorchamps on 25 June. The race, which started in pouring rain, was again won by Hermann Lang, who prevailed in his W 154 against his team-mate von Brauchitsch and the Auto Union of Rudolf Hasse. The V12 engine of Lang's racing car was equipped for the first time with a single two-stage compressor. The race was overshadowed by Seaman's serious accident, with the Briton succumbing to his injuries the following night.
Lang's winning streak, and that of the entire Mercedes-Benz racing team, came to an abrupt end in the next European Championship Grand Prix, the Grand Prix de l'A.C.F. held on the high-speed circuit in Reims on 9 July. None of the three W 154s that started, all powered by the latest engine version with two-stage compressor, completed the full race distance. While Caracciola had to retire already on the first lap after sliding off the track, first von Brauchitsch and later Lang came to a halt with engine damage. Instead, Auto Union drivers H. P. Müller and Georg "Schorsch" Meier, both former motorbike stars, set the scene with a double victory for the Zwickau team.
This was followed on 26 July by the German Grand Prix, the third of four European Championship races and a mass rally staged by the National Socialist ruling powers in accordance with the circumstances of the time. After the disastrous performance in Reims, the Mercedes-Benz team was under particularly high pressure. In the end, Rudolf Caracciola managed one of his brilliant wet races: with a lead of almost one minute, he secured victory in his W 154 ahead of H. P. Müller in an Auto Union Type D. As the two top finishers had each been the only starters remaining in the race for their teams, third place went unexpectedly to Paul Pietsch in a Maserati 8CTF.
The last race of the season, which was part of the European Grand Prix Championship, was the Swiss Grand Prix on the Bremgartenwald Circuit in Bern, which was particularly risky in wet conditions. The Mercedes-Benz racing team was represented with four cars, as was their toughest rival, the Auto Union team. The format of the race was unusual in that two separate qualifying heats were initially held for vehicles in the voiturette class with a displacement of up to 1500 cc and for 3-litre Grand Prix cars. The six fastest starters in the voiturette class and the 11 fastest 3-litre cars then together formed the field for the decisive race.
The Mercedes-Benz team with its W 154s left no doubt about its superiority on the Bremgarten Circuit. On a wet road, Caracciola this time had to yield to Hermann Lang, who kept the upper hand in a tough duel fought right up to the finish line to win by a lead of only around three seconds. Manfred von Brauchitsch rounded off the convincing performance by the Stuttgart team with third place.
Although Germany had triggered the Second World War two days earlier, the Belgrade Grand Prix on 3 September 1939 took place as planned with the participation of both German works teams. However, the starting field was limited to just five vehicles: two Mercedes-Benz W 154s, two Auto Union Type Ds and a privately entered Bugatti. The winner of the race, which had become obsolete from a sporting point of view, was Tazio Nuvolari in an Auto Union ahead of Manfred von Brauchitsch and the second Auto Union driver H. P. Müller.
The return of the Stuttgart racing entourage to the factory was already extremely difficult due to the war and was only managed with a delay via alternative routes. It is said that the trucks were requisitioned by the Wehrmacht immediately after their arrival. This marked the end of an era of great success in motorsport history for Daimler-Benz AG. It was not until 15 years later, in the 1954 season, that Mercedes-Benz returned to Grand Prix racing at the highest level, having already successfully competed in sports car races in 1952 in the newly developed 300 SL.