Mercedes-Benz 300 SL (W 194), 1952
After the watershed of the Second World War and the difficult resumption of regular vehicle production during the second half of the 1940s, Daimler-Benz AG in late 1950 began to look at opportunities for renewed involvement on the international motorsport scene, which was once again starting to blossom. The driving force behind these efforts was the then Chairman of the Board, Wilhelm Haspel. His credo was that the successful participation of Mercedes-Benz vehicles in well-known racing events served to strengthen the company's reputation on the one hand and represented an important sales promotion measure on the other, especially with a view to the urgently needed better development of export markets.
Initial attempts to participate in the Formula 1 World Championship, which had been held since 1950, with a newly designed 1.5-litre V12 racing car were stopped internally as early as autumn 1951. The background to this decision was the then unresolved future of the Grand Prix formula, which had been in force since 1947 and was scheduled to run until the end of 1953, and whose effective period had long been the subject of controversy both within and outside the responsible motorsport bodies. In the event that the extension favoured by the German and British sides did not materialise – a circumstance that did indeed occur – there were justified concerns that the high investment costs would not pay off in the end if the newly designed racing car could only be used for a single season.
As early as June 1951, Daimler-Benz also took a different and, as it turned out, highly successful route to challenge the competition again on a motorsport level. The focus was on sports car racing, which had taken off internationally in the post-war period. Road and circuit races such as Mille Miglia, the 24 Hours of Le Mans and the highly lucrative Carrera Panamericana across Mexico, which was launched in 1950, not only attracted hundreds of thousands to the courses, but also met with a great response worldwide. In addition, a number of new players such as Ferrari, Lancia and Aston Martin were on the scene, raising the bar for the company from Untertürkheim.
Another advantage of a factory involvement in sports car races that should not be underestimated was the fact that the development costs for the racing vehicles remained manageable, as they were not pure prototypes. Rather, the technical regulations stipulated a certain close relationship to series production for important components; however, the latter were defined in detail.
In his capacity as head of the testing department and former technical director of the racing department, Rudolf Uhlenhaut came up with the idea of using technical components from the two Mercedes-Benz 300 (W 186) and 300 S (W 188) top-of-the-line models and combining them with an innovative frame concept and an aerodynamically optimised sports car body. Supported by the concentrated expertise of the Mercedes-Benz design team and the testing department, Uhlenhaut clearly saw the potential to create a racing sports car that, despite some limitations, could at least compete on an equal footing with, for example, the vehicles from Ferrari, which were tailored much more specifically to the purpose.
After the Daimler-Benz Board of Management decided in the early summer of 1951 to have special bodies manufactured for such a project, the conceptual contours of the vehicle quickly took shape. Just under six months later, in November, chief engineer Fritz Nallinger already described the constitutive elements of the design. The aim was to create a lightweight, low-drag, low-profile body. The chassis would be a "tubular frame" in which the familiar six-cylinder engine would be installed at an angle in order to keep the overall height as low as possible. Other standard components would be the gearbox, both axles and the brake system from the 300 S. On this occasion, the model series code of the new racing sports car was also mentioned for the first time, which was to go down in automotive history a little later as the forefather of all Mercedes-Benz SL models: W 194. The model designation was 300 SL, with the number 300 denoting an engine capacity of 3 litres in accordance with the Mercedes-Benz passenger car nomenclature system and the abbreviation SL standing for "super-light", thus declaring a lightweight version of the 300 S, so to speak.
The roots of the M 194 engine used in the 300 SL go back to the pre-war years. Originally planned as a passenger car engine and used from 1941 onwards for light-duty commercial vehicles, the 2.6-litre in-line six-cylinder M 159 served as the design basis for the later racing engine.
Although the valve control by means of a bottom-mounted camshaft and long pushrods prevented higher revs and thus sustained increases in power, an ingenious idea of lead engine designer Wolf-Dieter Bensinger nevertheless opened up possibilities for increasing the power volume of the six-cylinder engine. By making a diagonal cut across the combustion chamber, Bensinger created more space for larger valve discs and, as a result, an improved gas cycle.
Further development work by mid-1950 included an increase in displacement from 2.6 to 3 litres and the transition to an overhead camshaft, which – thanks to the existing hemispherical combustion chambers complete with V-shaped overhead valves – significantly boosted the power output of the engine, which now bore the designation M 186. In this form and with a peak output of 115 hp/85 kW, the engine made its début in the new Mercedes-Benz 300 prestige vehicle, which was unveiled at the first International Motor Show (IAA) in Frankfurt am Main in April 1951. Equipped with a three-carburettor system and higher compression, the power unit already provided a maximum output of 150 hp/110 kW under the designation M 188 in the 300 S sports car model series, which celebrated its première at the Paris Motor Show in October.
For use in motorsport, the engine was fitted with a dry sump lubrication system with separate oil tank, which guaranteed optimum lubrication stability even in extreme conditions. In addition, the now absent oil pan favoured a particularly low installation position of the six-cylinder engine. This version of the six-cylinder engine, specified for sports purposes only, was given the designation M 194.
Since the engine was still a relatively simple series-production unit in spite of some adaptations to the special purpose – in contrast, for example, to the V12 power packs from Ferrari, which were produced in far smaller numbers and designed much more specifically – it was by no means easy for the developers to bring the three-litre up to a competitive performance level. Above all, the focus was also on unconditional reliability, which was even more decisive than superior engine performance in endurance races such as Mille Miglia or the 24 Hours of Le Mans.
The aim was to get as close as possible to the 200 hp/147 kW mark. To achieve this goal, the search for power focused on a few key areas: the carburettors, the camshafts and the compression ratio. For use in the Carrera Panamericana in Mexico, it was also possible to increase the displacement to 3102 cc by increasing the bore size by 1.5 mm, as the rules of the race did not stipulate an upper displacement limit.
In the five races of the 1952 season, the 300 SL racing sports car always competed with specially configured engines, the fine-tuning of which depended on the character of the respective event and the available fuel mixture. After promising trials with Weber carburettors had been terminated because the revolutionary in-house development of petrol direct injection seemed ready for use in the short term, all engines were equipped with three Solex carburettors. The maximum outputs of the M 194 engines used in the races varied considerably. They ranged from 162.5 hp/120 kW to 180 hp/132 kW at 5600 rpm in each case.
A special role was played by the supercharged engines that had been created in the run-up to the Nürburgring Anniversary Grand Prix for Sports Cars. By turbocharging the three-litre engine, the M 194's performance potential for sprint races was to be upped significantly. The version with the own designation M 197 produced an impressive 230 hp/169 kW at 6400 rpm, but was not able to compel with flawless reliability during test drives. In addition, the high power output of the M 197 pushed the chassis of the 300 SL racing sports car to its limits. In the end, the long shadow of petrol direct injection led to the discontinuation of all further development work on the supercharged engine.
However, engine performance that was adequate in a competitive environment was only one side of the coin. A particularly low vehicle weight and the best possible aerodynamics of the vehicle body played at least as important a role for the developers in achieving the desired success. Rudolf Uhlenhaut had already thought long and hard about a completely new frame concept for competition vehicles in the early post-war years. The tubular frame he devised made use of thin-walled round tubes of various diameters, which, when combined in groups of three, produced an immensely torsionally stiff yet lightweight tubular structure that supported all the technical components as well as the bodywork. The tubular frame designed by Uhlenhaut for the 300 SL racing sports car weighed only between 64 and 68 kg, depending on the version, and was thus lighter than all frame designs used to date.
The design of the 300 SL racing sports car ultimately corresponded to the idea of what an aerodynamically favourable coupé body should look like, which was shaped by theoretical and above all practical knowledge. The finishing touches, such as the issues of general driving stability, engine compartment ventilation or underbody panelling, were handled by the body development specialists. A unique feature of the first five vehicles was the small entrance hatch, the ancestor of the classic gullwing door, so to speak, which had become necessary due to the tall trellis structure of the tubular frame. Alfred Neubauer, the Mercedes-Benz racing director, had already studied the regulations extensively beforehand and declared this design solution to be unobjectionable. It was in this form that the 300 SL was presented to the international press on the Stuttgart to Heilbronn motorway on 12 March 1952, well before the start of the motor racing season.
A characteristic feature of the first five vehicles was the small entrance hatch, the ancestor of the classic gullwing door, so to speak, which was the result of the lattice structure of the very tall building tubular frame. Racing director Alfred Neubauer had already studied the regulations extensively beforehand and declared this constructive solution to be unobjectionable.
In connection with the body of the 300 SL racing sports car, there were three special features in the course of the further development. The most poignant was the introduction of gullwing doors, which will forever be associated with Mercedes-Benz in automotive history. The implementation of this modification was the brainchild of Raymond Acat, Sports Secretary of the "Automobile Club de l`Ouest", the organiser of the "24 Hours of Le Mans", whom Alfred Neubauer had contacted in advance. However, it was undisputed that the original hatches would also have complied with the regulations. Neubauer had written to Acat about this on 3 April 1952: "We have allowed ourselves to do this because, as you rightly point out, it does not contravene the provisions of the regulations. [...] However, in order to spare you and us any difficulties during inspection and approval in Le Mans, we have decided to modify the bodywork of our cars as you suggested with a sketch in your letter of 14 March."
However, the original entrance hatches on the 300 SL racing sports car were probably not only changed to enable a smooth approval, but also because they made it easier to get in, which was an advantage that should not be underestimated in a Le Mans start. The first vehicle to be built with the larger gullwing doors was the car with chassis number 6, which was used for the first time just four weeks before the endurance classic in France: in the Bern Prize on 18 May 1952, where it finished 3rd with Fritz Rieß at the wheel.
The second special feature involved tests with a so-called air brake, which was also fitted to the vehicle with chassis end number 6 before the 24-hour race in Le Mans, which was scheduled for 14/15 June 1952. In order to relieve the drum brake system of the 300 SL (W 194) during racing, a brake flap anchored on two pylons was mounted on the roof of the car. When not in use, the flap lay flat, but during braking manoeuvres from higher speeds, it could be raised by the driver with the aid of a hydraulic actuator and braced itself against the airstream at a 90-degree angle. Although this resulted in considerably improved deceleration values and protection of the vehicle brake, the anchoring of the large-format brake flap on the roof was judged to be not fully perfected in view of the considerable force exerted in the activated position. As a result, testing was put on hold for the time being.
For the first race of the 300 SL (W 194) on home soil, at the beginning of August 1952 in the Nürburgring Anniversary Grand Prix for Sports Cars, a third special feature was added to the bodywork. The four 300 SL models that lined up at the start of the race were specially developed roadster versions. In order to save weight, the roof superstructures of three of the four cars were cut off and a spartan open cockpit was designed, which could be implemented as a one or two-seater, depending on the race. The fourth roadster was built as such and was also characterised by a wheelbase shortened by 200 mm and reduced track widths at the front and rear. The aim of this measure was to create a version of the 300 SL racing sports car that was not only lighter, but also more compact and easier to handle. Apart from the race on the Nürburgring, the roadster version was only used one other time: a regular wheelbase example driven by the pairing Fitch/Geiger started in the Carrera Panamericana in Mexico in November 1952, but did not score any points there because Fitch had gone back in reverse immediately after the start of the penultimate stage to have a few final corrections made and was disqualified as a result.
As far as the chassis specifications of the new racing sports car were concerned, the development team made use of the 300 (W 186) and 300 S (W 188) production models. At the front, the trapezoidal-link axle, a Mercedes-Benz in-house design that had been tried and tested since the mid-1930s, was used. At the rear, the well-known double-joint swing axle, first realised in 1931, took over the wheel control function. Both chassis elements were modified in detail for use in a competition vehicle, but with increasing engine power and in demanding racing and testing, the limits of the basic design quickly became apparent, not least due to the reduced track widths at the front and rear compared to the production models. Unsatisfactory tracking and camber stability of the rear axle when cornering at speed and considerable traction problems when accelerating out of tight corners – sometimes more and sometimes less pronounced, depending on the event – were constant companions of the Mercedes-Benz factory drivers in the 1952 racing season.
The drum brake system of the 300 SL racing sports car was better able to withstand the rigours of racing. By widening the brake drums, the brake surface had become significantly larger compared to the standard 300 and 300 S vehicles; in addition, the ribbed aluminium brake drums were cast using the Alfin process and had greater heat resistance. Although the brake system of the W 194 was not the limiting factor in any of the racing events in 1952, the disc brake technology used for the first time by Jaguar in a racing car that year foreshadowed that – in motor racing at least – the era of the drum brake was gradually drawing to a close.
The racing calendar of the Mercedes-Benz factory team provided for a start with several 300 SL racing sports cars at each of five events. Since the contest of strength with the competition, especially Ferrari, was less about sheer engine power and more about absolute reliability and meticulous preparation, the focus was primarily on endurance races. Mille Miglia in Italy and the 24 Hours of Le Mans in particular seemed to be ideal terrain to demonstrate the qualities of the new car – not least in view of the worldwide exposure these events received.
The Carrera Panamericana in Mexico at the end of November remained an equation with many unknowns, which admittedly enticed with exorbitant starting and prize money. As an extremely demanding road race, which was held on the American continent to boot, it nevertheless fitted in well from a sporting and strategic point of view. The agenda was completed by two sprint races. Both the Bern Grand Prix and the Nürburgring Anniversary Grand Prix for Sports Cars were support races within a Grand Prix weekend and thus of limited sporting value. Here, the presentation of the new Mercedes-Benz racing sports car in front of a home crowd was more of a priority.
The return of a Mercedes-Benz factory team to the big international motorsport stage began with a bang at the beginning of May 1952. With three 300 SL models driven by the pairings Kling/Klenk, Caracciola/Kurrle and Lang/Grupp, the Untertürkheim team faced the strongest local competition at Mille Miglia. The cars, driving talent and local knowledge of the Italian opponents made a successful performance by the Mercedes-Benz team at its first major appearance after the end of the war seem anything but foreseeable.
Nevertheless, the elaborate preparation, extensive test drives, including on the ground, the flawless reliability of the new racing sports cars and, last but not least, the driving skills of Karl Kling and Rudolf Caracciola led to a success hardly thought possible: Kling/Klenk finished second just over four minutes behind the Ferrari team Bracco/Rolfo, and Caracciola/Kurrle came in fourth in the final standings.
Spurred on by this result, the Mercedes-Benz factory team took to the starting grid two weeks later with no less than four W 194 models for the Bern Grand Prix, which was held as a sprint race on the dangerous course in the Bremgarten Forest. The field of participants, which consisted almost exclusively of private drivers, was unable to put up any resistance, and Karl Kling, Hermann Lang and Fritz Rieß thus achieved an unchallenged triple victory. The race was overshadowed by the serious accident involving Rudolf Caracciola, who crashed his car into a tree and suffered such serious injuries that he had to end his splendid career as a result.
The third race of the season was the legendary 24 Hours of Le Mans in mid-June. After a factory-supported start by Rudolf Caracciola in 1930 in a Mercedes-Benz Type SS, which ended in retirement after 85 laps, this incarnation of the automotive endurance race had not been on the agenda of the Mercedes-Benz racing department since then, despite its worldwide significance. Currently, it fitted perfectly into the product profile of the new and already so successful 300 SL racing sports car.
Three cars with the driver pairings Lang/Rieß, Helfrich/Niedermayr and Kling/Klenk challenged the assembled world of top-class racing cars, including the international driver elite. After 24 hours and 3733.78 kilometres covered, the sensation was complete: Mercedes-Benz took a superior one-two victory with Lang/Rieß and Helfrich/Niedermayr in the 300 SL. Only the duo Kling/Klenk had not managed the distance due to technical problems. The qualities of the car, coupled with the excellence of the technical as well as organisational preparation and capable drivers in every respect, had led to the first motorsport success of the Mercedes-Benz factory team in the post-war period that attracted worldwide attention.
It wasn't until the beginning of August that the enthusiastic home crowd at the Nürburgring got the opportunity to admire the internationally sensational Mercedes-Benz 300 SL racing sports cars in action. Although the Anniversary Grand Prix for Sports Cars was not a serious sporting challenge due to the lack of a strong field of participants, the Untertürkheim factory team wanted to offer something special on German terrain. However, the original plan to have two 300 SL models with supercharged M 197 engines compete for the first time was dropped due to doubts about the reliability of the engines that arose at short notice, and the use of the supercharged engines remained limited to practice. So the Nürburgring only saw the première of the roadster versions. Three of the four open-top racing sports cars brought to the start had the standard wheelbase, while one had the significantly shorter 2200 mm wheelbase.
After the start flag dropped, the race took the expected course: The 300 SL (W 194) models fought each other to win the Anniversary Grand Prix and to the delight of the throngs of spectators took the first four places in the order of Hermann Lang, Karl Kling, Fritz Rieß and Theo Helfrich.
The last race of the season at the end of November proved to be a real adventure for the Mercedes-Benz racing department. Not much was known about the Carrera Panamericana, which was held for the first time in 1950, except that it led over more than 3000 kilometres of public roads across Mexico, sometimes at the highest speeds. It was also clear that the course was partly at a high altitude and that the organiser had offered princely sums as starting and prize money. Although neither the local conditions nor the quality of the starting field, which largely consisted of US vehicles, could be assessed with any certainty, they dared to participate, especially with a view to the publicity effect of a good performance on the American continent. The considerable sums offered as starting money also made it possible to justify the huge amount of preparation, logistics and expense involved in the expedition, as racing director Neubauer quite aptly described the race in Mexico.
The company boldly tackled the Carrera Panamericana with three 300 SL racing sports cars – two coupés and a roadster with standard wheelbase – and the driver teams Kling/Klenk, Lang/Grupp and Fitch/Geiger. Although many problems that arose on site had been solved in advance, such as the question of the optimal fuel mixture or the best engine setting for sections at high elevations,numerous imponderables remained – for example the durability of the tyres at high continuous speeds on Mexican roads.
Also not predictable was the incident that befell the Kling/Klenk car on the very first stage of the race and found its way into universal motorsport history. A vulture startled by the approaching 300 SL swooped down on Kling and Klenk's coupé, which was travelling at 200 km/h, hit and smashed through the windscreen, causing Hans Klenk to suffer facial injuries. As a result, the vehicle was unceremoniously fitted with vertical metal bars in front of the newly installed windscreen at the end of the day to prevent any further impacts.
However, this dramatic event in no way prevented the Kling/Klenk team from continuing to put pressure on the leading Ferrari as the race progressed. After five gruelling days of racing and eight stages with average speeds of up to 213 km/h, what was hardly thought possible was accomplished: Not only the Kling/Klenk team, but also the Lang/Grupp driver team had subdued the stubborn opponents from Italy and ensured a double victory for the Untertürkheim factory delegation. The only 300 SL (W 194) in roadster specification, driven by the American-German crew of John Fitch and Eugen Geiger, finished with the fifth-fastest overall time, but did not classify due to an unintentional breach of the regulations at the start of the penultimate stage.
The results of the first post-war motor racing season under the company's auspices could not have been better for Daimler-Benz. The 300 SL racing sports car turned out to be a smash hit – despite being much more closely related to series production than the racing cars used by the toughest competitors. Four wins and a second place in five race appearances were a clear message to the world of motor racing: Mercedes-Benz was back after a hiatus of more than 10 years and undoubtedly still had great plans.