<div class="htmlview paragraph"><b>M</b>ARKED improvement in high-speed high-efficiency engines will be accomplished during the next few years, according to the author. They will have better balance, longer life and greater efficiency, and will develop more power and be more satisfactory to the motoring public. Details of recent developments in this class of engine are given by the author after remarking that the present trend is toward a large number of small changes in design and construction rather than toward radical departures from former design and methods.</div> <div class="htmlview paragraph">Mr. Duesenberg comments upon the main features of design of his 91-cu. in. racing-car engine and its parts, and on the troubles that necessitated design changes. The combustion-chamber is stated to be the most important contributor to high efficiency. If the shape of the combustion-chamber, the area of the valves, and the location of the valves and spark-plugs are not right, all the other refinements of detail are of little value. The inlet manifold is second in importance, particularly with present-day fuels, and becomes of even greater importance as the speed of the engine increases. There is no hard and fast rule by which to work, as the firing order and the length, size and number of bends in the manifold affect the performance. Apparently the manifold that gives best top-speed performance does not give best results at low speed, and the manifold for best economy does not give high-speed performance. Unless a manifold can be perfected so that double carburetion becomes practicable, the author sees no means of obtaining correct air-fuel mixtures at all speeds.</div> <div class="htmlview paragraph">Valve area is a controlling factor for high speed unless a supercharger is used, in which case the pressure created by the supercharger can offset to some extent a deficiency in valve area. Shape of the valve, its circumference and the surrounding contour of the cylinder-head all play an important part.</div> <div class="htmlview paragraph">In the discussion the author gives further details and cites some of his experiences while testing engines and parts of new design. Engine lubrication and heat dissipation, supercharging and methods for lubricating superchargers also are discussed.</div>