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  Mercedes-Benz W25K      

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Country of origin:Germany
Produced in:1936
Predecessor:Mercedes-Benz W25
Successor:Mercedes-Benz W125
Author:Wouter Melissen
Last updated:July 21, 2009
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Click here to download printer friendly versionFor Mercedes-Benz the arrival of a new German government in 1933 and a thoroughly revised rule-book for the 1934 season provided the final push to build a Grand Prix car for the first time the Daimler and Benz merger. Appalled by the defeat at Avus in May of 1933 to the French and Italians, the new 'Reichs Chancellor' made a substantial amount of money available for a German Grand Prix team. Surprisingly, Mercedes-Benz was not the only German manufacturer to jump on the opportunity; the newly formed Auto Union conglomerate also ventured into Grand Prix racing with a Ferdinand Porsche designed machine. Devised to slow the cars down and make racing saver, the new regulations dictated that a Grand Prix car could have a maximum dry-weight of just 750 kg. Work on the new Mercedes-Benz 'W25' Grand Prix racer had already started back in March of 1933, so it seems the government incentive offered after the Avus-rennen was just an added bonus.

The new regulations meant that the German engineers had to find a balance between outright performance and weight. Simply put; they had the fit the biggest possible engine in the lightest available chassis. Yes that does not sound very safe at all. Following the successful Alfa Romeo and Bugatti Grand Prix engines, a supercharged, twin-cam, eight-cylinder engine was chosen. Unlike the contemporary designs, the new 'M25' Mercedes-Benz featured a head with four valves per cylinder. Following Daimler-Benz design practices, the engine itself was constructed from two groups of four separate forged-steel cylinders. The sheet-steel water-jackets and valve-ports were welded to the individual cylinder. Also typical for Daimler-Benz was the unusual carburation; the supercharged air from the single Roots-type blower was fed through the carburetors. Just like the earlier S-Type Mercedes', the new W25's supercharger produced a very recognizable whine. Displacement was just under 3.4 litre, which was enough to produce 302 bhp on petrol. When fed with more exotic, alcohol-based brews, the output rose to 354 bhp.

The M25 engine alone already weighed in at just over 200 kg, so saving weight on the rest of the car was paramount. Using two longitudinal box-section beams, the chassis itself was a rather conventional affair. The two box-section frame was reinforced by several cross-members and a cross-tube at the front. Its lightness was ensured by drilling numerous holes in the frame. The all-round independent suspension did break new ground. At the front very short double wishbones were fitted, while the rear-end featured swing-axles. Springing at the front was by coil springs that were actuated by bell-cranks and fitted horizontally inside the cross-tube. The bottom wishbones were attached to friction dampers. The swing axles were controlled by short transversely mounted quarter-elliptic leaf springs and friction dampers. The four-speed gearbox was combined with the final drive. Braking was provided by hydraulic drum brakes sourced at Lockheed. Like the chassis, all of the small bits were cross-drilled to keep the W25 under the 750 kg maximum. The rolling-chassis was covered in a thin alloy skin. Cowlings over the radiator and suspension gave the car a very aerodynamic appearance.

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  Article Image gallery (2) Specifications