Few classic vehicles are as well recognised as the 1950s Mercedes 300SL
gull-wing. Perhaps it's the novel vertical-opening doors, the exhilarating
driving experience or the undisputed historical significance. Whatever it is, you
can see why enthusiasts are prepared to spend up to AUD$1m for their slice of
gull-wing action...
The gull-wing story begins in the wake of the Second World War. Through the
late 1940s, Mercedes (actually Daimler-Benz at the time) survived by
manufacturing re-hashes of the pre-war utilitarian sedans and trucks. It was far
from glamorous but it was, at least, survival.
The desire to re-emerge as one of the world's greatest car manufacturers
became evident at the 1951 Frankfurt Motor Show. Here, Mercedes revealed the new
220-series sedan and the all-important 300-series luxury saloon. Although still
sharing much of the basic design of earlier models, the 300-series instantly
became the car of the rich and glamorous.
With a finger back in the luxury pie, Mercedes turned its attention to
motorsport - an arena where it had been so successful with its silver arrow cars
during the '30s.
Initially, Mercedes attempted to challenge the other exotic car manufacturers
(such as Ferrari and Jaguar) with old 1939-design racecars that survived the
war. There simply wasn't enough money to design an all-new racecar at this time.
Not surprisingly, the 1939-spec cars were completely off the pace and a big
engineering effort was required to be successful.
Mercedes reluctantly decided to build a new vehicle to compete in the Sports
Car category and, interestingly, it was Jaguar that provided direction for the
design. Jaguar had won the 1951 Le Mans using nothing more than stock XK120
driveline and suspension components in a lightweight chassis – so Daimler-Benz
took a similar route using its existing 300-series components. This car was to
become the W194.
With a target weight of less than 820kg, Daimler-Benz began the W194 project
by constructing a complicated space-frame chassis. To achieve a high level of
structural rigidity, deep truss sections were incorporated on each side of the
passenger compartment. This resulted in a very high door sill – hence fitment of
the famous vertical-opening (aka gull-wing) doors.
Engineers were by now very aware of aerodynamics, so the W194's new body was
designed with minimal frontal area and an efficient profile. Part of aerodynamic
development involved canting the engine a massive 50 degrees to achieve a low
bonnet line.
Following the Jaguar formula, Mercedes used the existing M186-design engine
as used in the production 300-series saloon. Displacing 3.0-litres, the engine
was relabelled M194 and tuned for the 1952 race series to deliver 128kW and
256Nm (at 5200 and 4200 rpm respectively). Triple Solex down-draught carbs and a
relatively high 8.0:1 compression ratio were employed, together with an
aggressive camshaft profile. Numerous changes were made during the 1952 race
season, including use of dry sump lubrication.
The car's 4-speed manual gearbox and driveline were essentially the same as
those fitted to the 300-series.
Meanwhile, the W194's brake system design was carried over from the heavier
300-series. The diameter of the drums went unchanged, but they were widened to give a total pad
area of 258 square inches (1664cm2). This arrangement is said to be the pinnacle
of drum brake performance at the time.
Amazingly, the W194 racecar was developed in just five months! It was a
monumental effort but, unfortunately, the sub-820kg goal was missed by more than
45kg. Mercedes' race drivers said they could never win without more power to
offset the extra weight, but engineers were confident the car could make up for
this with its handling and aerodynamics.
They were right.
At its first motorsport appearance the W194 was a huge success. Sure,
Mercedes had enlisted some of the world's best drivers, but you can't argue with
consecutive podium finishes. With barely a hint of a challenge, the W194 won the
1952 road race season. Only eleven W194s had to be built to achieve this
success.
About this time, Mercedes was under immense pressure to build a road-going
production version of the W194. The company was very reluctant to pursue
this idea since the car was never intended for production and its short
gestation period meant it was a little raw around the edges. This initial
reluctance was overcome by several hundred advance orders from one of the
American distributors...
Mercedes agreed to produce a road version of their race-winning design - but
only after it could be thoroughly revised for its new application. This vehicle
was to become the 300SL.
Amongst these revisions was the remedy of major heat and noise issues,
extensive body restyling (with some aluminium panels), a smaller fuel tank and
attention to cargo space. The cabin was equipped with only two seats.
Interestingly, the 300SL was the first production car to successfully employ fuel injection. Daimler-Benz, in conjunction with Bosch and the Reich Air
Ministry, had experimented with fuel injection during the Second World War. The
primary aim was to eliminate fuel starvation in air combat as well as to improve
performance. The 300SL used a piston-type injection pump and incorporated many
of the design principles learnt when experimenting with aircraft. Huge 17-inch
ram induction tubes also replaced the conventional carby-style intake manifold.
Because its engine had been canted by 50-degrees, the W194 racecar suffered
poor access to the spark plugs. The production 300SL uses a redesigned SOHC
cylinder head with relocated spark plugs and various changes to accommodate the
fuel injection system. A forged steel crank, large sodium-filled exhaust valves
and a more efficient exhaust layout were also employed. Interestingly, ignition
timing could also be retarded in-cabin if the driver encountered a bad batch of
fuel. The result of all this was around 160kW at 5700 rpm and 280Nm of torque at
4500 rpm. This engine became the M198, but much of the architecture was still similar
to the M186 found in the original 300-series.
Amazingly, these production cars generated more power than the 1952 race cars.
It's just as well, because they also weighed an extra 270+ kilograms...
The road-ready 300SL first appeared alongside the smaller 190SL cousin at the
International Motor Sports Show in New York, 1954. Immediately, the 300SL caused
a storm with its impressive styling and amazing gull-wing doors. The 300SL was immensely expensive,
costing almost twice the price of the smaller 190SL...
Production of the 300SL began in late 1954 and it continued until it was
replaced by the 300SL Roadster (convertible) in 1957. Around 1400 300SL
gull-wings were built. Apparently there were numerous changes during its
production span and 29 all-aluminium bodied examples were built in early 1955.
These were around 80kg lighter.
The 300SL was (and remains) a vehicle that people love to drive. The car
does, however, have a reputation for abrupt oversteer from its "branch guidance
pendulum rear axle". To some extent, this may have been sensationalised by
American buyers who were more accustomed to understeer - but there's no denying
that the 300SL requires a delicate touch at high speed. Theoretical top speed
was 260 km/h. The 300SL gull-wing is also widely criticised for its awkward
entry/exit – a hangover from the fact the car was never design for general use.
When assessed logically, the replacement for the 300SL gull-wing – the
Roadster - was a better all-round vehicle. It had a much lower roll-centre,
softer springs, the steering ratio was revised (from 2 to 3 turns lock-to-lock)
and the side truss frames were lowered, allowing fitment of conventional
side-swing doors. Engine output was increased to up to 187kW and the final drive
ratio was shortened, although an extra 90kg of bulk offset any performance gain. Sales
of the 300SL Roadster were limited by an unaffordable price tag – not to mention
much of the gull-wing's initial impact and charisma had since passed.
In just three years, one of the world's greatest cars had come – and gone.
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The W196 and W196S Race Cars
Following its 1952 Sports Car racing success with the W194, Mercedes entered
Formula racing in 1953.
Limited to an engine capacity of just 2.5-litres, Mercedes designed a
2.5-litre straight-eight - with a 9000 rpm redline. This extremely high engine
speed was made possible by a power take-off located at the centre of the
crankshaft (effectively forming two in-line fours bolted together) and an
interesting desmodromic valve action. This used two cam lobes per valve - one
directly above the valve that caused it to open and another that closed it via a
rocker arm. This set-up eliminated valve float problems.
Like its predecessor, the W196 proved to be another racing success.
Next came the W196S (aka 300SLR), which was continued to be almost invincible
throughout the 1955 season. The engine was enlarged to 3.0-litres and, with a
tremendous amount of power, it won every road race it entered. The only
exception is the notorious 1955 LeMans, in which one of the Mercedes drivers and
80 spectators were killed in a crash. The morning following the
incident Mercedes withdrew from the event and discontinued Sports Car and
Formula racing.
Only nine W196S racecars were built and, due to the horrific LeMans crash,
only eight survive. These remain the ultimate vehicles in the series.
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