AMG Mercedes-Benz 300SEL 6.8 'Rote Sau'

The AMG Mercedes-Benz 300SEL 6.8 was the accumulation of about 500 hours of detailed work and many years of engineering experience.

AMG set about building the car according to the new 1970 Touring Car Regulations, which was a mix of the old Group 2 and Group 5 Special Touring Car regulations. A brief summary:

Only cars with a minimum production run of 1000 units were eligible to enter.
The original seats, door panels and dashboard had to be retained.
A rev counter could be added to the dashboard.
The driver’s seat could be changed to a sports racing seat.
Four point 'H-pattern' seat belts had to be fitted.
Bumpers could be removed.
Wider wheels and wheel arches could be fitted.
No superchargers and fuel injection was allowed, unless a standard feature of the car.
Boring of the engine was allowed provided it was not more than the stated capacity category for that car, i.e. up to 1300cc; 1300cc – 2000cc, over 2000cc
Mechanical parts had to remain OEM, but lightening, balancing, removal by machining or changing the shape by machining of these parts was allowed. Adding material, mechanical extension or treatment of the materials resulting in a change of molecular structure, or change in surface of the metal was not allowed
Cylinder heads had to be OEM, but valves, guides and valves seats were free.
No four-valve cylinder heads were allowed, unless a standard feature of the car.

AMG bought an accident damaged 300SEL 6.3 and using a new body shell, started the build. The wheel arches were extended to accommodate the magnesium wheels from the experimental Mercedes-Benz C111. These rims were 10” wide for the front fitted with 4.50/13.00x15 Dunlop Racing tyres and 12” wide at the rear fitted with 5.50/13.00x15 Dunlop Racing tyres.

A roll cage by Matter was made and installed, and other modifications were made to strengthen the body shell.

To save weight, the bumpers were left off and all the glazing was replaced with Plexiglass, including the windscreen. Further weight was saved by making the doors from aluminium and the car ended up weighing 1635kg – standard was 1765 kg.

An auxiliary fuel tank of 15 liters was fitted inside the boot, which required further modifications to the body on the right rear flank to accommodate the fuel filler neck.

The standard interior remained, including rear seat, door panels and dashboard – all with the original wood trim. A Motolita steering wheel replaced the original with a standard Mercedes-Benz pad and logo, and a Recaro racing seat with four-point seat belts was installed to replace the original driver’s seat.

Four powerful Bosch spotlights were fitted for night racing with an external central cut-out switch installed in the right front valance, as per racing safety regulations. The bonnet and boot were secured in the closed position with external rubber catches.

The brake booster remained, as well as the standard twin circuit braking system. However, larger front brake callipers and discs were sourced and fitted. Ferodo DS11 brake pads were used to replace the original ATE pads.

The standard air suspension and power steering were retained, but smaller and harder air bellows were installed to firm up and lower the suspension. Racing Bilstein shock absorbers were also fitted along with larger anti-roll bars front and rear.

Several modifications were made to the engine. The capacity of the engine was increased from the standard 6300cmᶟ to 6835cmᶟ by boring the cylinders from 102mm to 105mm. The cylinder heads were skimmed to increase the compression ratio and the inlet and exhaust tracts were polished for better flow. The camshafts were modified and the valves were lightened, but kept the same size. The standard crankshaft was used as were the conrods, although they were lightened and polished. Everything was then finely balanced. A separate inlet manifold per bank was made, each with its own air mass meter, and the Bosch mechanical injection system was retained. All of these modifications resulted in an increase in power from 250Hp to 428Hp, and an increase in torque from 500Nm to 608Nm.

A manual gearbox conversion was done using a ZF 5-speed S5242 gearbox, as found in Maseratis and Aston Martins of that period. Gearbox ratios were: 1st 2.75; 2nd 1.79; 3rd 1.23, 4th 1 and 5th 0.833. Reverse was 2.73. The flywheel and clutch assembly were adapted using a Sachs commercial vehicle unit. Power was transferred via a special propshaft to a standard differential with a ratio of 2.69, 70% slip and an adapted oil cooler. There were spare diffs with ratios of 2.82 and 3.89.

During testing at Hockenheim, the 300SEL 6.8 achieved the following performance figures:

0-100km/h 6.1s

0-160km/h 12.6s

0-200km/h 19.8s

Top speed 265km/h

Theoretical top speed at 6000rpm: 282km/h

Fuel consumption: 37l/ 100km

The AMG 300SEL 6.8 had a bit of a chequered racing history. Its most famous triumph was the result at Spa in 1971, but after that the results were inconsistent.

A rule change came into effect for the European Touring Car Championship at the end of the 1971 banning cars with an engine capacity over 5 litres, so this ruled the 300SEL 6.8 out from any further competition in this championship. Nevertheless, the AMG was tested for Le Mans in March 1972 and entered two non-ETCC races later in that year at Nürburgring and Norisring where the ban on 5 litre capacities was not applicable.

By the end of 1972 the AMG 300SEL 6.8 had reached the end of its useful life as a racing car, and AMG reached a deal with Matra, the French aeronautical company, who bought the car after some significant modifications were made. Matra required a special vehicle to use as a mobile laboratory to test the coefficient of friction on aircraft undercarriages, and the requirement was that the vehicle had to have significant acceleration and top speed to simulate aircraft starting and landing scenarios. The car was lengthened and converted into a six-door sedan to accommodate all the test equipment, along with a life-size wheel that was dropped through a hole in the floor onto a runway surface. It is unknown what became of the car, but it’s assumed that it became redundant and was scrapped.