Mercedes-Benz Auto Union
The Auto Union racing cars types A to D were built as Grand Prix racing cars from 1934 to 1939. They resembled the earlier Benz Tropfenwagen, also built in part by Rumpler engineers), The only Grand Prix racers to wear Auto Union's four-ringed logo, they were particularly dominant in 1936. From 1935 to 1937, Auto Union cars car won 25 races, driven by Ernst von Delius, Bernd Rosemeyer, Hans Stuck Sr., and Achille Varzi. Much has been written about the difficult handling characteristics of this car, but its tremendous power and acceleration were undeniable — a driver could induce wheelspin at over 100 mph (160 km/h).
The cars used supercharged piston engines; eventually producing almost 550 hp (410 kW; 560 PS), designed to provide optimum torque at low engine speeds. Rosemeyer would later drive one around the Nürburgring in a single gear, to prove the engine was flexible enough to do it. The fuel tank was located in the centre of the car, directly behind the driver (who would be placed well towards the front), so the car's front-rear weight distribution would remain unchanged as fuel was used — exactly the same location used in modern open-wheel racing cars, and for the same reason.
The chassis tubes were initially used as water carriers from the radiator to the engine, but this was eventually abandoned after they often sprung small leaks.
Source: Wikipedia, 2012