There was no surprise in January 1914 when Mercedes announced its entry in the French Grand Prix at Le Mans. Daimler-Motoren-Gesellschaft, makers of the Mercedes brand, hadn't had a factory racing program since 1908, but had attempted to return for 1913, when their three-valve cars were disqualified on an entry technicality.
The July 4, 1914, French GP was shaping up to be one of the major races of the year, with all the big European makes submitting their entries, most with two- or three-car teams. DMG went all out, however, with a massive five-car effort, the most allowed under the rules. And while they had to adhere to the 1,000-kilogram (2,425-pound) minimum weight/4.5-liter (274.6-cu.in.) maximum displacement formula under which all cars had to run, the specifics were entirely veiled in mystery.
After Christian Lautenschlager, Louis Wagner and Otto Salzar swept the podium in astonishing style, public interest in what was underhood became clamorous, but even on pit lane immediately following the victory, Mercedes kept the cars under close guard. Unlike the wild streamlining of many leading cars, the Mercedes appeared relatively conventional. Clearly, there was some extraordinary engineering involved, but it was only after several weeks of pressure that they released details, and much like the copycat new-car magazines of today, the car magazines of 1914 all ran essentially identical stories and photographs of these extraordinary machines.
As did most competitors, Mercedes opted for a hemi, a steel cylinder and head four-cylinder, but it was an extremely long-stroke engine, 93 x 165mm bore and stroke (3.6 x 6.49 inches)--only Peugeot had a smaller bore, at 92mm. Yielding 4.33 liters or 264.24 cubic inches, the individual steel cylinders were machined from separate forgings, with steel waterjackets welded on. A single overhead camshaft operated 16 big valves, of an estimated 1.6/1.7 inches in diameter. Triple spark plugs completed the highly perforated head, and DMG actually had provisions for four, fired in sync.
A bronze camshaft housing was bolted to the head of the cylinders, with a detachable cover above each cylinder, held down by four bolts carrying the rockers. The rocker ends projected through the housing with external springs. The camshaft, carried in ball bearings, was driven by a vertical shaft at the rear of the engine that turned by a pair of bevel gears from the crankshaft; the upper bevels were in an aluminum housing. The five-main-bearing camshaft was drilled for oil distribution; additional oiling came from numerous additional leads and, in addition to the crankcase, there were two reserve oil tanks, one with a foot-operated plunger. That pump also delivered supplemental oil to the front U-joint and the water pump. Located low at the back of the engine and driven by a transverse shaft, twin Bosch double magnetos provided spark to the 12 plugs.
While dynamometer tests existed, horsepower at the time was listed according to the A.L.A.M. rating, calculated using the square of the bore times the number of pistons, divided by 2.5. To save you the trouble, this gave the Mercedes 20.75hp. In reality, it was more like 115hp at 3,200-3,500 RPM (which it maintained for more than seven hours in the race), incredibly high for the time, especially considering the half-foot stroke.
It was a shot heard round the world, and many great engineers acquired M 93654 engines to study, including one Walter Owen Bentley. He ended up with long-term possession of a demonstration model during the war, and reverse engineered it, both for Bentley automobiles and Rolls-Royce aero engines. The cars themselves stuck around, too: American legend Ralph de Palma was so impressed that he bought one for his personal use, and, among his many victories in the chassis, notched up the win at the 1915 Indianapolis 500. Even in the Twenties, it was still competitive: De Palma's car was victorious in the 1922 Targa Florio, where it competed against DMG's own 1.5-liter supercharged entries. These phenomenal Mercedes M 93654s were fundamental in establishing the company's enduring reputation for quality and innovation.
This article originally appeared in the February, 2011 issue of Hemmings Motor News.
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