Mercedes-Benz Grand-Prix racing car W 154, 1938

Mercedes-Benz Grand-Prix racing car W 154, 1938

With the introduction of a new racing formula for single-seater Grand Prix cars in 1938 - which was also adopted for the AAA National Championship held in the USA - a paradigm shift took place in the top flight of international motor racing. With the reform of the regulations announced in October 1936, the automobile umbrella organisation AIACR (Association Internationale des Automobile Clubs Reconnus) pursued the goal of being able to better control the development of the engine and thus driving performance, which had seen an explosive rise with the introduction of the 750 kg Formula in 1934.

Instead of the minimum technical restrictions of the 750 kg Formula, there was now a variable limitation of the car weights depending on the displacement, which this time were defined as minimum weights. Naturally aspirated engines from 1000 cc to 4500 cc and supercharged engines from 666 cc to 3000 cc were permitted, each of which was assigned certain minimum vehicle weights (excluding fuel, oil and coolant). The intention of this list, drawn up in steps of 100 cc by the AIACR, was to create as uniform a power/weight ratio as possible despite a wide variety of engine sizes and concepts. No specifications were made regarding the number of cylinders or other important characteristics of the power unit. The choice of fuel was also open.

For Daimler-Benz as well as for its persistent domestic competitor Auto Union, the new set of rules meant that immense efforts had to be made from autumn 1936 onwards, on the one hand to continue the current racing operations with success and, on the other, to be able to develop a new racing vehicle for 1938. The technical and budgetary level reached in the meantime was so high that, apart from the two German participants, only the French car and truck marque Delahaye - economically strengthened by not inconsiderable subsidies from the French government - saw itself in a position to enter the races of the new formula with a specially constructed car, the Type 145 with a 4.5-litre naturally aspirated V12 engine.

After an intermediate phase in which the Untertürkheim development team, thanks to re-established contacts with the Porsche design office, also carefully examined external concepts such as a mid-engine racing car with a 3-litre V12 engine or a 4.5-litre naturally aspirated engine with three cylinder banks of eight cylinders each in a W configuration, the Board of Management of Daimler-Benz AG decided at the end of July 1937 to develop the car in-house. The engine, called M 154, was designed as a V12 with two compressors and - in accordance with the new regulations - a maximum permissible displacement of 3 litres. The weight of the new car, which was designated W 154, thus had to be at least 850 kg without fuel.

The decision for a V12 engine was a logical step, despite the considerably higher engine speed level with only 3 litres of displacement: extensive experience with engines of this type was available from aircraft engine construction and the development of the 5.7 litre DAB engines, which were used in some record-breaking vehicles. The design engineers around Albert Heess were nevertheless guided for the most part by the traditional patterns of racing engine construction at Daimler-Benz. So they reverted to the highly durable but also heavyweight design in which the cylinders were welded to the cylinder head to form a single unit and had welded-on cooling jackets made of sheet steel. The cylinder bank angle of the new engine was an ideal 60 degrees in terms of vibration, with the six cylinders of each bank divided into two units of three - another classic solution for Mercedes-Benz racing engines.

The gas cycle of the V12, which was only slightly undersquare with a bore/stroke ratio of 67 mm x 70 mm, was provided by two mercury-cooled intake and exhaust valves each with a disc diameter of 30 mm. These were actuated via rocker arms by two overhead camshafts per cylinder bank driven by a spur gear cascade. The combustion mixture was ignited by a spark plug positioned centrally in the cylinder head.

Since the new design no longer had forked connecting rods - as the DAB V12 engines had - the M 154 again had the slight cylinder offset typical of V-engines, with conventional side-by-side connecting rods. Apparently, it was no longer important to save the last few centimetres of installation space.

In the area of mixture preparation, the designers' thoughts initially clearly wandered in the direction of direct petrol injection - a forward-looking technology in which the Daimler-Benz designers had done absolute pioneering work. However, its successful use in the series production of aircraft engines in 1937, with their less complex load behaviour, did not mean that such a fuel injection system with all its advantages could also be used without problems in motor racing, which placed the highest demands on the driveability of the engine.

As this would have required considerably more development time, the proven M 125 inline eight-cylinder engine was used as the model for the mixture formation, as the performance-enhancing properties of a naturally aspirated carburettor - positioned upstream of the compressor - compared to a downstream pressure carburettor had been clearly recognised and exploited accordingly. In the new M 154, therefore, a twin-barrel intake carburettor was installed upstream of the two superchargers, together with an additional slide carburettor. The two upright Roots blowers themselves were significantly smaller than those of the predecessor engines due to the smaller displacement. The height of the vanes was only 150 mm, their diameter 105.7 mm.

The highly specified technology of the new 3-litre V12 engine resulted in a power-to-swept-volume ratio that led to new dimensions. Whereas the previous inline eight-cylinder engines had a power-to-swept-volume ratio of around 100 hp/74 kW, the newly designed engine had a ratio of around 160 hp/118 kW. In absolute terms, the V12 engines provided a power volume ranging from 397 hp/292 kW to 483 hp/355 kW, depending on the model, compression ratio and compressor specification. The nominal engine speeds were 7800 rpm to 8000 rpm - no comparison to the rather leisurely 5800 rpm of the old eight-cylinder engines.

Of course, this level of power and engine speed took its toll in the form of astronomical fuel consumption. The mixture, which had a high alcohol content to ensure the best possible internal cooling of the engine and its peripherals, flowed through the carburettors in quantities of up to 150 litres per 100 kilometres of racing. This posed very special problems for the designers, as enormous amounts of fuel had to be carried in the vehicle if they wanted to manage with as few refuelling stops as possible during a race.

The much wider rev range of the M 154 and its changed performance characteristics made moving away from the 4-speed gearboxes that had always been used until then an inevitable step. Thus the new 3-litre Formula racing car featured a five-speed gearbox for the first time, which enabled the drivers to keep the V12 in the optimum torque window at all times.

The far-reaching further development undergone by the W 125 that had been so successful in 1937 in the areas of frame and suspension also benefited the new W 154. The concept of a ladder-type frame with multiple transverse bracings was adopted, the longitudinal members of which consisted of tubes with an oval cross-section. For the current 3-litre racing car, additional reinforcement plates were welded in between the rear engine mount and the rear of the frame for the purpose of further improving torsional stiffness. Tests showed that this increased the torsional rigidity by about 30%.

Starting from this basis, the designers focused their development work on significantly optimising the driving dynamics. As a means to an end, a further lowering of the vehicle's centre of gravity and a traction-enhancing axle load distribution needed to be achieved. The compact V12 engine offered much better conditions for this than the long inline eight-cylinder of the W 125. In the end, it was decided to tilt the new engine by 6.5 degrees to the right, as seen in the direction of travel, and at the same time slightly to the rear. As a result, the drive shaft running to the transaxle was offset strongly to the left and the driver's seat position was extremely low. In this ingenious way, both the desired lowering of the centre of gravity and the shifting of the axle load distribution slightly towards the rear axle could be realised.

Since the front and rear suspensions newly developed for the W 125 had proven themselves in real racing, there were no fundamental changes here for the W 154. At the front, the double trapezoidal links with coil springs and hydraulic dual-piston shock absorbers were retained; at the rear, the familiar torsion-bar-sprung de Dion axle with hydraulic dual-piston shock absorbers continued to be used. In combination with a wheelbase that had been slightly reduced by 68 mm to 2730 mm compared to the W 125, this design for the W 154 chassis resulted in driving behaviour that delighted the drivers right from the start.

Due to its weight, which despite all efforts to save weight had increased by almost 120 kg compared to the W 125, and the higher driving dynamics, the brake system of the W 154 with its four drums measuring 400 mm in diameter gradually reached its limits. As a consequence, the rear brake drums were enlarged to 470 mm diameter for some races.

A particularly difficult chapter in the W 154 development concerned the configuration of the fuel tanks. Since the high consumption values of the V12 meant that considerable quantities of the highly combustible fuel had to be carried on board, the question of their optimal placement, i.e. the one that, depending on the fill level, has the least influence on the handling, became the top priority. Rejecting tanks placed to the side of the driver for safety reasons, the design team opted for an innovative two-part solution consisting of a fuel tank called a "saddle tank" between the rear end of the engine and the driver, and a rear tank connected to it. The most favourable distribution of the total volume of around 400 litres deemed necessary for a Grand Prix between the two fuel tanks was the subject of extensive test runs.

Depending on the race and the personal preferences of the drivers in terms of the self-steering behaviour of the car, different configurations were chosen in the end. Initially, a large saddle tank and a small rear tank had been envisaged, but Hermann Lang and Manfred von Brauchitsch preferred the exact opposite layout because of the reduced tendency to oversteer. Rudolf Caracciola, on the other hand, was perfectly capable of dealing with an abruptly swerving rear end on the W 154, which is why his racing vehicle was occasionally fitted with a particularly voluminous saddle tank in addition to the large rear tank. This increased the total capacity of the fuel tanks to an impressive 475 litres.

The design of the tanks not only influenced the handling, but also the external appearance of the new 3-litre Formula racing car. In addition to the noticeably low silhouette, which was due to the special installation position of the V12 engine and made the W 154 appear to crouch low on the road, the different-sized fuel tanks led to changes in the lines and proportions of the vehicle. With a smaller saddle tank and large rear tank, the W 154 appeared perfectly balanced and highly elegant, whereas with a large saddle tank and small rear tank, it had a much more stocky appearance.

A total of fourteen W 154 chassis were built for the various races in 1938 and 1939. A fifteenth example was manufactured by Daimler-Benz from individual parts after the war and, alongside two pre-war examples of the W 154, was raced by the factory for the last time in Argentina in two formula-free races at an airfield circuit near Buenos Aires in mid- and late February 1951.

For the upcoming 1938 season, the then automobile umbrella organisation AIACR (Association Internationale des Automobile Clubs Reconnus), at the same time the supreme motorsport authority, had named only four races, the Grands Prix of Germany, Switzerland, Italy and - a new addition - the Grand Prix de l'ACF in Reims, as counting towards the European Championship. In addition to these, the Mercedes-Benz team's race calendar included starts in five other events, the Pau Grand Prix, the Tripoli Grand Prix, the Coppa Ciano as well as the Coppa Acerbo, both in Italy, and the Donington Grand Prix on the English circuit of the same name.

The season started for the Mercedes-Benz racing team right away in the first Grand Prix of the year on 10 April 1938 on the narrow street circuit in Pau in south-western France. For the opening race, two of the brand-new W 154s, just ready for action, were entered with Rudolf Caracciola and Hermann Lang at the wheel. Three other works teams, the undaunted Delahaye team with three of their 4.5-litre V12 145s, Alfa Corse likewise with three Tipo 308s with 3-litre inline eight-cylinder engines, and Bugatti with a single T59/50 took on the team from Untertürkheim. The race took a surprising course: René Dreyfus in the fastest Delahaye was able to keep up with Caracciola's pace and took the lead after the driver from Remagen had to stop for fuel. Hermann Lang, whose car had not been able to start due to problems, took over Caracciola's W 154, but was unable to catch the French local hero and had to settle for second place at the finish.

Five weeks later, on 15 May, the Tripoli Grand Prix followed on the Mellaha Circuit in Libya, which was then part of Italian territory. This time, the Untertürkheim team entered three cars for Caracciola, von Brauchitsch and Lang. Alongside Delahaye, Alfa Romeo and Bugatti, the Maserati factory team now also entered the big fray with the new Type 8CTF. However, the true performance strength of the W 154 became apparent on the fast circuit in North Africa. The superior triple victory in the order Lang, von Brauchitsch, Caracciola sent a signal for the further course of the season and gave an inkling that the new technical regulations, which aimed for the most uniform possible power/weight ratios in vehicles with different engines, would certainly not be able to create anything like equal opportunity under the given circumstances.

This race was followed on 3 July 1938 by the Grand Prix de l'ACF, which was part of the European Championship and was held on the high-speed circuit of Reims. Although the entry list had included a total of 19 participants, in the end only nine cars rolled onto the grid: four French and five German cars, namely three W 154s and, for the first time, two new Auto Union Type Ds with 3-litre V12 mid-mounted engines. While the Zwickau team struggled with problems and lost both cars early due to accidents, the Mercedes-Benz squad demonstrated its almost overwhelming dominance with another one-two-three win by von Brauchitsch, Caracciola and Lang. The lead of the top three over fourth-placed Frenchman René Carrière in a Talbot T150C with a 4.5-litre six-cylinder was no less than 10 laps.

Three weeks later, on 24 July, the next European Championship race took place, the German Grand Prix on the Nürburgring. Daimler-Benz had entered five W 154s, four of which eventually took part in the race. Auto Union brought four of its new mid-engined cars to the start. Other factory teams came from Alfa Romeo, which for the first time entered two of the new Tipo 312s likewise powered by a 3-litre V12, and from Delahaye, which competed in the Eifel with two of the familiar T145s with 4.5-litre naturally aspirated V12 engine.

It was to be a turbulent race, marked by a series of accidents and mishaps by the favourites. History remembers von Brauchitsch's pit stop, which ended with a brief inferno, fortunately without serious injury, when the invisibly burning petrol racing mixture suddenly ignited. The surprise winner was the Briton "Dick" Seaman, who brought his W 154 across the finish line without any damage after 22 laps of racing. Second place went to Hermann Lang in Caracciola's car. The Remagen native had had to give up due to indisposition. Third and fourth places went to Auto Union, whose new Type D could not yet match the pace of the W 154.

The Coppa Ciano and the Coppa Acerbo were the next two non-European Championship races on Italian soil on the Mercedes-Benz racing team's calendar. For the Coppa Ciano, held at the beginning of August 1938 on a circuit near Livorno, Auto Union had cancelled its participation after the disappointment on the Nürburgring. With Hermann Lang, Rudolf Caracciola and Manfred von Brauchitsch, there were three W 154s on the grid.

Conte Trossi put in a strong performance, not only being fastest in practice with his factory Maserati 8CTF, but also maintaining the lead for several laps in the early stages of the race. The Alfa Romeo Tipo 312s also showed significant improvement. Giuseppe Farina in particular demonstrated the potential of the twelve-cylinder Alfa by finishing third, less than 50 seconds behind. Manfred von Brauchitsch was declared the winner, but after he was disqualified for using unauthorised assistance, the victory was later awarded to Hermann Lang, who had actually finished in second place. Caracciola had retired about halfway through the race due to a defect.

The start at the Coppa Acerbo was already on the agenda for the following weekend. The race, held on a triangular course near Pescara, confirmed the somewhat more differentiated picture of the balance of power that the Coppa Ciano had given. Although Rudolf Caracciola scored a commanding victory in the W 154, Giuseppe Farina in the Alfa Romeo Tipo 312 once again achieved a brilliant result with second place, while the two cars of Lang and von Brauchitsch as well as all three Auto Unions had to retire early.

Another week later, the tight race calendar scheduled the Swiss Grand Prix as the next European Championship race. Heavy rain made the fast course in Bern's Bremgartenwald a highly risky challenge. Nevertheless, the Mercedes-Benz trio consisting of Rudolf Caracciola, "Dick" Seaman and Manfred von Brauchitsch managed a clear one-two-three victory in the most difficult conditions, with Caracciola once again impressively demonstrating his special talent as a masterful driver in the wet. Stuck, driving the last remaining of the original four Auto Union Type Ds, finished fourth, just ahead of Farina in the factory Alfa 312.

Even before the final round of the European Grand Prix Championship, it was clear that no one would be able to take the championship title away from Rudolf Caracciola and his W 154. With two second places and one victory, he topped the standings, in which his three main rivals, Mercedes-Benz team-mates Hermann Lang, "Dick" Seaman and Manfred von Brauchitsch, had already fallen behind due to non-participation or retirements.

The race, which started on 11 September 1938 on the high-speed circuit of Monza, took a disappointing course for the team from Untertürkheim. While Seaman, Lang and von Brauchitsch had to retire with technical problems, Rudolf Caracciola, who was still not fully recovered, battled his way adamantly through despite sliding off the track and handing the car over to von Brauchitsch for a while in the middle of the race, and was still able to secure third place at the finish, three laps behind. The local racing hero Tazio Nuvolari, now under contract with Auto Union as the successor to Bernd Rosemeyer, who had been killed in a record-breaking run, managed the first victory for the new mid-engined Type D just a few seconds ahead of Giuseppe Farina, who again put in a strong performance, in the new Alfa Romeo Tipo 316 with a 3-litre V16 power unit.

As in the previous year, the hilly circuit of Donington Park in the British Midlands was the venue for the last Grand Prix of the 1938 season, which, however, no longer counted towards the European Championship. The Donington Grand Prix was able to provide further proof of the clearly improved competitiveness of the Auto Union Type D. Tazio Nuvolari also managed a victory there with the mid-engined car, without benefiting from any lucky circumstances. Second and third places went to Lang and the British local hero Seaman in their W 154s. Rudolf Caracciola did not even make the trip to Great Britain due to illness. Alfa Corse, the Alfa Romeo factory team, also stayed away from the race. The three remaining factory cars, Luigi Villoresi's Maserati 8CTF and the two Delahaye T145s, retired with technical defects.

The 1938 racing season had proved to be the most successful in recent company history for Daimler-Benz. It was widely characterised by the absolute dominance of the W 154 and had brought Rudolf Caracciola his third European Championship title after 1935 and 1937. By the end of the season, however, there were clear signs that the competitors from Zwickau with their powerful mid-engined cars were again threatening to become a persistent challenger the following year.

Loading