Guide: Mercedes-Benz CW311
Background
When Mercedes-Benz launched the W198 300 SL in 1954, their high performance Gullwing-doored Coupe was arguably the most exciting motor car available. A little under three years later, it morphed into the slightly more refined 300 SL Roadster. Unfortunately, when production ended in early 1963, a like-for-like replacement never materialised.
Mercedes ultimately went on to use the SL moniker for a line of handsome Convertibles that sold in vast numbers, but for which speed and handling was much less important than aesthetics, comfort, build quality and reliability.
The arrival of the C111 design study in 1969 brought renewed hope that Mercedes were about to offer a highly anticipated successor to the W198. However, the firm stood fast in their decision not to offer the C111 to the public; instead, this radical line of concept cars were used purely for research and development purposes.
The lack of a true successor to the W198 Gullwing had not gone unnoticed by Porsche engineer, Eberhard Schulz.
Schulz had started work at Porsche’s Design Studio in 1971. He had been given a job after he drove to the interview in his home-made Erator GTE, a two-seat mid-engined Coupe built on a custom tubular steel spaceframe chassis with a Gullwing-doored GRP body.
While Eberhard Schulz never worked for Mercedes, he had a deep fascination with the firm having grown up during the post-war Silver Arrows era that yielded the original W194 300 SL of 1952, the dominant W196 Formula 1 cars of 1954-1955, the all-conquering W196S 300 SLR of 1955 and the W198 SL production cars.
Like so many Mercedes enthusiasts, Schulz yearned for a true successor to the W198 Gullwing and, in 1972, he began work on his own interpretation of such a machine. He decided on a mid-engined rear-wheel drive configuration with lightweight fibreglass body and fitted the most powerful Mercedes-Benz engine of the time.
With the design stage complete, Schulz partnered with BB Auto Exclusiv Service in Frankfurt to bring his idea to fruition. BB was run by brothers Rainer and Dieter Buchmann. Established in 1973, BB quickly became the go-to outlet for custom paint, engine and interior modifications.
BB came to international prominence in 1976 when they began to offer Targa variants of Porsche’s recently introduced 911 Turbo (930). Porsche themselves only offered the 930 as a Coupe, but BB did a roaring trade creating bespoke Turbos for their wealthy customers.
It was around this time that Schulz teamed up with BB to make his dream a reality.
Dubbed CW311, the new pearlescent white Mercedes-badged prototype was unveiled at the Frankfurt Motor Show in September 1978 and generated a massive amount of publicity.
Chassis
Schulz designed the CW311 around a tubular steel chassis with an aluminium centre cell. At 2400mm, the wheelbase was extremely short for a mid-engined configuration.
Independent suspension was was via double wishbones at the front with upper and lower transverse links at the rear. Coil sprung tubular shock absorbers were fitted all round along with anti-roll bars at either end.
There were also power-assisted outboard ventilated disc brakes.
Many of the sundry parts required for assembly were imported from Porsche and Mercedes.
Power steering was deemed necessary for manoeuvring the massively wide alloy wheels. The fronts were 10-inches across while those at the back were 13-inches. They had a 15-inch diameter and were of BB’s turbine style that had been designed to direct cool air to the brakes. Pirelli tyres were fitted. Track dimensions were 74mm wider at the front of the car.
The fuel tank was a massive 120-litres.
Engine / Gearbox
In the engine bay was an AMG-tuned version of the 450 SEL 6.9 power unit that had been in production since 1975.
From the factory, these 90° V8 engines came with a cast-iron block, aluminium alloy heads and single overhead camshafts with two valves per cylinder. They also featured a forged crankshaft, connecting rods and pistons plus dry-sump lubrication.
Displacement was 6834cc thanks to a bore and stroke of 107mm and 95mm respectively. With a compression ratio of 8.8:1 and Bosch K-Jetronic continuous fuel-injection, peak output was 282bhp at 4000rpm and 406lb-ft at 2800rpm.
Enhancements carried out for the new AMG version included high lift camshafts, a revised intake system, an increased compression ratio and a switch to Bosch mechanical fuel-injection. A custom side-exiting spaghetti exhausts system was also installed.
As a result, peak output soared to 370bhp at 5100rpm and 417lb-ft at 3000rpm.
From 1979, AMG went on to offer this engine (albeit with Bosch K-Jetronic fuel-injection) as part of an enhanced 450 SEL 6.9 package.
Instead of the three-speed automatic gearbox used by the 450 SEL 6.9, the CW311 was hooked up with a five-speed ZF 5DS 25/2 transaxle complete with single-plate clutch and limited-slip differential.
Bodywork
Schulz designed a sleek body for the CW311 that was manufactured from fibreglass and bonded to the chassis. The car took its name from a drag coefficient of 0.311.
Several features were a homage to famous Mercedes of the past, most obviously the enormous Gullwing doors and exhausts that exited down the left-hand flank ahead of the rear wheel.
The design was characterised by its short overhangs and a sleek overall appearance devoid of the blisters and spoilers that could be found on most super sports cars from this era.
At the front was a wide intake aperture that housed the indicators and a body coloured three-pointed star accessorised with a pair of whiskers. Further up the nose, retractable headlights featured blanking panels that unusually dropped down into the body.
One particularly innovative feature was the CW311’s bumper-less impact-absorbing front and rear aprons.
Instead of traditional exterior mirrors, Schulz added a roof-mounted periscope above the driver. The side windows were fixed in place.
A flat rear deck contained cut outs for the engine to poke through. On either side were a pair of wide flying buttresses that swept down to the truncated tail.
At the back, Schulz fitted tail lights from the R107 / W116. Two large rectangular sections were cut away for cooling purposes.
Interior
Inside, single piece Recaro bucket seats were sunk between the high, wide sills and the tall transmission tunnel. Upholstery was a mix of dark blue leather, chequered two-tone fabric and matching carpet.
The instrument binnacle featured corners angled inwards towards the driver. It housed a full complement of instrumentation plus the ventilation controls and a state-of-the-art audio system.
Despite the extremely high specification, space was limited, access was difficult and visibility was poor.
Weight / Performance
As a result of its compact dimensions and lightweight fibreglass body, the CW311 tipped the scales at just 1250kg. Despite the massive engine, it also had a near perfect 48/52 weight distribution.
Top speed was 198mph and 0-62mph took just 4.9 seconds. Neither Ferrari, Lamborghini, Porsche or Aston Martin had anything as fast in their product line up.
Subsequent History
Despite the CW311’s positive reception at Frankfurt, Mercedes were not interested in putting the car into production.
Over the next couple of years, development work continued at the BB workshops, during which time the CW311’s cockpit was modified to incorporate a full range of high end electronics.
Along with a number of other BB products, the CW311 also went on to figure prominently in the 1980 movie, Car-napping.
Soon afterwards, Schulz and BB parted ways.
In 1982, Schulz formed the Isdera company which went on to display a production-ready long wheelbase version of the car, now called the Imperator 108i, at the Geneva Motor Show in March 1984.
Around 30 Imperators were subsequently built by Isdera over the next nine years.
Text copyright: Supercar Nostalgia
Photo Copyright: BB
