TECHNOFILE WEBERS DCO CARBURETTOR
BEFORE THE ADVENT OF FUEL INJECTION, RACE TEAMS LOOKED HIGH AND LOW FOR THE PERFECT CARBURETTOR. AS KEITH HOWARD REPORTS, THE SOLUTION CAME FROM ITALY photography by Charles Best
here are few components boasting a thoroughbred racing pedigree which you could, or would want to, employ on a road car. But one item with just such a background encompassing five Fl championships as well as countless successes in other arenas has proved itself uniquely egalitarian, for decades being synonymous with readily available and adaptable bolt-on power: the Weber DCO twin-choke sidedraught carburettor. Introduced at the dawn of the 1950s, the DCO doppio corpo orizontale, meaning double-bodied horizontal wasted little time proving itself a winner in the most exalted company. In 1952 and ’53 it racked up its -first Fl world championships in the Ferrari Tipo 500, repeating the success in 1957 in the Maserati 250F and in 1959 and ’60 in the T51 and T53 Cooper-Climaxes. Although other carburettor makers Solex, SU, even Amal competed alongside it in the premier racing formula, Solex claiming a championship in the Lancia-Ferrari in 1956, Weber dominated thmugh both the DCO and various downdraught models like the DC’N L, which substituted far it in vet-engined applications. Founder Edoardo Weber’s long-standing relationship with Enzo Ferrari, with whom he had already worked prior to farming Weber Carburatori in 1924, meant that racing featured high on Weber’s list of priorii’s, great care being expended on making the throats
its carburettors as aerodynamically efficient as possible. Available with throat diameters from 35 to 58mm, the DCO was also unusually flexible. With hindsight, nevertheless, it might seem odd that the DCO was given the opportunity of winning Fl world championships right up to 1960. (Weber’s last championship success, appropriately with Ferrari, came in 1961 but with bespoke triplechoke downdraught 40IF3Cs provisioning the Sharknose’s V6.) In 1954 and ’55 Mercedes-Benz had proved the worth of fuel injection in the victorious W196s, and Vanwall had repeated the lesson in 1958. On the face of it, by the time the Coopers tarried the DCO to victory the carburettor was already outmoded. But this is an oversimplification: you have to bear in mind the relative crudity of fuel
injection systems of the time, and understand the significance of changing fuel regulations.
When Mercedes won in 1954 and ’55, potent alcohol blends were still legal. As these were a lot less sensitive to variations in fuel :air ratio than unadulterated petrol is, the relatively inexact metering of fuel by the Bosch injection system although it was a good deal more sophisticated in this respect than the American Hilbom-Travers continuous spray alternative, as Connaught discovered didn’t matter a great deal. What was important was that fuel injection removed the carburettor’s need for a venturi (choke) in the inlet manifold, thereby improving engine breathing. This situation didn’t last, though. The fuel rules changed for 1958, outlawing alcohol blends, with
the result that high.-octane Avgas (aviation gasoline) became the fuel of choice. Not only did engine powers fall as a result, mixture control also became much more critical. Vanwall succeeded using the Bosch injection system nonetheless, but it was a close run thing. Then the rules tightened still further, insisting on fuel more akin to what the ordinary motorist used as specified by the FIA.
None of this tinkering with fuel regs would have mattered much were full load, wide open throttle perfarmance the only issue: in this respect fuel injection continued to offer an advantage. But as Wally Hassan of Coventry Climax was to explain in a lecture to the Society of Automotive Engineers in 1966, “If the use of engine performance is studied… it is evident that the time during which the car operates at maximum rpm and power is extremely small.
The most successful engine is, therefore, the one which combines a good maximum power with exceptional torque spread.” For so long as the carburettor enjoyed an advantage in the latter respect due to its superior fuel metering or suffered no significant disadvantage it still had life in it.
Not that the carburettor itself was without quirks. As cornering forces increased as a result of improved tyre technology, lowered centres of gravity and more enlightened suspension design, teams began to report problems caused by fuel surge in the float chambers. For those who remembered the Battle of Britain it was a curious echo of what happened when the carburetted Spitfire met the fuel injected Messerschmitt Bf109. Pulling negative g in a Spit caused its Merlin engine to hesitate sufficiently for a diving Bf109 to make its escape. RAF pilots overcame this by performing a half-roll to convert negative into positive g unfortunately, not a manoeuvre with a race track equivalent.
Eventually, of course, the carburettor’s game was up. Lucas introduced its superior ‘shuttle type’ fuel injection metering unit with which BRM won the F1 title in 1962 and Lotus the fallowing year, and the DCO was history. Even Ferrari finally embraced fuel injection, albeit by Bosch, during the 1963 season.
Today we live in an era where arranging for precisely the tight amount of fuel to be introduced into the cylinder, whatever the engine speed or load, is no more complex than entering the appropriate figure into the engine management’s look-up table. The fiddly, inexact and, let’s not forget, costly business of juggling main, air-corrector, slow-running, pump and starter jets, emulsion tubes, choke sizes and accelerator pump strokes has been superseded by plugging numbers into digital memory. And by any measure that’s welcome progress.
Remarkably, though, Weber still exists (now as a division of engine management specialist Magneti Marelli) and the DCOE the best-known DCO variant, produced in by far the largest numbers remains in production. Not only to satisfy the replacement market, either. For significant numbers of hands-on car enthusiasts, particularly those tuning an engine with a reactionary original equipment fuel injection system, the DCOE remains one of the most cost-effective ways to bolt on performance. Our world isn’t all computer controlled yet. CI