Arizona republican., 1918-08-18

means simply the dead weight of tho part, which must be overcome by the propulsive medium. For instance, the piston each time it makes a revolution, reaches what is known as dead center, top and bottom. At this point.i it ends its travel in one direction and is about to begin travelling in the opposite .di- rectiOn In other words for a fraction of time it is at rest. This is inertia and it takes an appreciable portion of the power generated to overcome this force. In order to assist the propulsive force to overcome the inertia, the re- ciprocatins parts must be made as light as possible, if high speed is to be ob tained within the power plant.
 For this reason high speed power "lants employ pistons made of steel aluminium or of very light cast iron section. Aluminium is a very desirable metal, which is being largely used. in spite of it's present high cost In the same way light rods and other similar parts must be employed in the high speed engine.
 Another factor to be considered in obtaining high engine speed, is tho ability of the power plant to use gen erous quantities of fuel This means that an extra l3rge quantity of fuel must be taken in. must be thoroughly burned and the burnt gases must be completely expelled For this reason the inlet valves of the high speed en- zine are made extra large and the in let passages are so designed that the flow of gas from carburetor to com hustion chamber will be straight and free. There must be no sharp turns. nor any constriction to hinder the passage of tho gas. In some high speed engines the flow of gas approaches 200 feet per second.
 Valves Must Be Liqht
 It will also be obvious that in a high speed power plant, the valves must be as light as possible, to obtain the sharp snappy action needed in this system operating at extreme speed The valve timing must be absolutely accurate. The design of the combustion chamber will also exert a considerable influence on the operation of the engine It is necessary that combustion be as near ly instantaneous as possible For this reason the combustion chamber is usu- ally made in the form of perfect sphere. The L-head construction with it's offset chamber is taboo for this reason. the valve in-t the head being the accepted design.
 In the extremely high rate of rcvou- ton in the high speed engine. the crankshaft will he subject to unusual efforts at distortion. For this reason if must be balanced to offset the forces that arc trying to pull it out of shape. This method of balancing the crank shaft with cOunterweights is considered preferable to the other method of mak- ing it extra heavy to withstand the pressure put upon it.
 The multiple cylinder engines, the siXes, eights and tWelves are simply one way of Securing high engine speed and many of them operate at as high as 5000 revolutions per minute. In this way they give what is practically an even and uninterrupted flow of power strokes, which makes for smoother op- eration.
 In considering the question of engine speed as it relates to efficiency, it must be remembered that there is a peak point. up to which the power of the motor increases with it's increasing revolutions and beyond which tho