A MERCEDES-BENZ CHANGE

The design of Grand Prix racing-cars is by no means nearing stagnation, as we shall endeavour to show when we again discuss the trend of design at the end of the year. In. the meantime, Mercedes-Benz have made an important change that merits discussion, namely, they now suck mixture from the carburetter instead of blowing through the carburetter. A new, very special carburetter of Mercedes-Benz design is used. Mercedes-Benz, as everyone knows, pioneered supercharging for production model cars and we believe that they introduced a blown touring model even before they exploited forced-induction for racing. For ordinary use ‘they decided that the supercharger would be best arranged to be largely out of action and accordingly they devised the classic clutch-operated system, whereby the blower was only engaged at wide throttleopenings, a system that enabled the blower to increase both acceleration and speed, yet to operate only under conditions that were least likely to impair economy or to result in over-stressing, or prolonged over-filling at inopportune piston velocities. The supercharger was arranged to suck from the carburetter, as being the best way of arranging for the change over from atmospheric to forced induction, and this layout is still used to this day for the Type 540 K Mercedes-Benz, in conjunction. with the clutch engagement, after figuring on all production blown Mercedes models, four, six and eight cylinder. The same layout was used, logically, on. the blown Bearcat Stutz with clutch-engaged blower, although in this case the forced induction could be introduced at any throttle opening. Blowing through the carburetter, according to a Sunbeam engineer years ago, resulted in the greatest possible improvement in acceleration ; it also obviated fuel deposition bothers. But, obviously, Merced.es-Ben.z and Stutz both used this layout primarily because, although it involved complicated pressure-balancing of fuel-tank and float-chamber, it was the better arrangement for use with clutch control. To-day, of course, Atalanta makes use of the more conventional layout, sucking from the carburetter, in conjunction with clutch control, the blower engagement being possible at all throttle positions. This entails a duplicated arrangement of intake maulfolding with automatic change-over valves incorporated therein. Incidentally an Arnott compressor and carburetter are now used by Atalanta. For racing purposes Mercedes-Benz had always blown through the carburetter, even in the case of the modern G. P. cars with the blower permanently in action. Now comes news that they have changed over to the universal, from-the-carburetter method. No doubt the greater simplicity, resulting from elimination of pressure-balancing, has something to do with this change, while for racing work, of course, mixture inter-cooling presents no counter problems

affecting distribution. There is no indication that the famous clutch-controlled, air-through-the-carburetter system, which many eminent engineers regard as the most practical means of applying forced-induction to a touringtype car, will be abandoned by MercedesBenz for their production models-.