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COMPRESSION ratios will increase gradually to about 8:1 for small spark-ignition engines and 7:1 for large engines as fuel improvements permit, engineers estimate. This increase will probably be accomplished with some sort of valve-in-head design. The higher ratios will call for better cooling to prevent detonation and more rigid construction for shock control. The tendency toward increased deposits will be curbed by better piston rings, closer-fitting pistons, cooled valves, and cooled spark plugs. In fuel systems, the ultimate aim is a simple, easily serviced, moderately priced fuel-injection system. Meanwhile, pressure carburetion is likely to be the next advance. Fuel pumps in or near the tank would give the higher pump pressure needed for pressure carburetion and improve atomization and distribution. Supercharging to increase power by raising compression pressure instead of compression ratio will be thoroughly investigated.

MR. TAUB predicts that the time for intensive work on the fuel-economy problem, such as has been done recently in England, is near at hand because of the imminence of increased fuel taxation. Tank mileage, he explains, depends on the ability of an engine to utilize lean mixtures- not just lean mixture from the carburetor, but modification of an engine to burn these lean mixtures without interference with flexibility or performance in any way. A study of what happens in the combustion chamber is cited as the major opportunity for engineering improvement in the ability to burn lean mixtures. In his discussion of his work at Vauxhall Motors, Mr. Taub considers wide gaps and their effect on ignition lag, long-reach spark plugs, tappet adjustment, effect of higher compression ratios, variation per cycle, detonation, and means of forecasting combustion roughness.

VARIATION in engineering practice between European and American motor cars is to be expected. Many of these differences are brought about by local conditions and must be accepted. However, there are practices that vary from the American that do not justify themselves by result or local conditions. The two outstanding are bore wear and carburetion. This paper deals only with the high spots of these two differences.

THE fuel consumption prevailing today is no better than it was five years ago. Higher road speeds are responsible. Cars in the hands of owners today are below potential economy between 10 and 15 per cent. Minor adjustments can correct this. Phasing of the burn with valve and piston movement is necessary for economy. Spark-plug position relative to the whole chamber is important. Spark-plug points position inward is important. The spark-plug gap width must be worked out. Mixture “fish hooks” to determine leanest mixture that will burn without raggedness, are the yardstick. Mixture distribution is important. The attitude of today is that a specific type of manifold does not exist. The manifold must be “tailored” to fit individual conditions. Offside mixtures out of the carburetor is real problem of distribution. Exhaust dilution of the mixture is the handicap to clean operation with lean mixtures. Timing is the most important avenue of progress.

VIBRATION formerly was classed as such without much thought as to the determination of its sources, Mr. Taub states, and then came isolation of the various causes. The first two vibrations to be segregated and vigorously attacked were the secondary inertias of reciprocating units and torsional vibration. The development of the six-cylinder engine was among the earliest attempts to eliminate secondaries, and it was also the earliest producer of torsional vibration. Dynamics, combustion roughness, torsional roughness and structural weakness, are a few of the contributing causes of engine roughness. Consideration must be given to all these factors if an engine is to be considered inherently smooth, and each is analyzed. Engine mountings should have low resistance to rotation about the longitudinal principal axis and to rotation about the vertical axis through the center of gravity, together with minimum shift of affective principal axis and vertical axis.

AS engineering standards have risen, the need for production ingenuity has become greater than ever before. The engineer looks to the shop for major assistance in realizing his ideals of improved products. He expects the shop voluntarily to reduce the variations from dimensional specifications and to improve its facility to meet changes in design. Refinement in design is useless unless the shop can accurately hold the dimensions. Powerplant characteristics are largely controlled by the accuracy of centers and roundness and straightness of bores in cylinders and bearings. Crankshaft balance, quiet valve tappets and uniformity of weight and fit of reciprocating parts are all dependent upon accuracy of machine operations. To be able to make design changes in the product without great expense is vitally important. Tools must be designed with facility for change. Fixed-center boring machines are to blame for considerable engine trouble and may make design changes prohibitively expensive.

HOPING that discussion and dissemination of information on the fundamentals of distribution routine will continue, the author reiterates known facts, which include (a) the method of charting distribution progress, (b) a suggestion for locating the error in distribution and (c) a series of thoughts on construction. The paper is divided into two parts, the first being a study of distribution routine and the other a discussion of a few of the problems that are met every day in the search for perfect distribution. Complete satisfactory distribution and the quantitative measurement of its quality are the two major problems of distribution. The interrelation of these problems is mentioned and the complexity of the subject of distribution is emphasized by listing nine detailed factors, the point being made that if the information that engineers have on these items could be collected and codified considerable progress would be made.

AN ENDEAVOR is made herein by the author to prove by argument and charts based on data that the greatest result per dollar of car cost is obtained by the greatest piston displacement obtainable per dollar expended rather than by the greatest horsepower per dollar. Maximum result per dollar is a major principle of economics, but horsepower per dollar and piston displacement per dollar are controversial economic fundamentals. The latter is declared to be the accepted principle in the low-price car field, and the author asserts that it should be accepted in the high-price field. Price class controls the cost of the powerplant, and ingenuity of the engineering and manufacturing departments will control piston displacement. The trends in the different price classes as regards car weight, piston displacement, ratio of weight to piston displacement, and potential and actual performance in the items of economy, durability, acceleration and speed, are shown by charts and discussed.

PREVIOUS papers on Combustion-Chamber Design by three leading authorities on the subject showed enough points of real or apparent disagreement to leave the designing engineer in doubt on many of the details of design which they discussed. The author of this paper was asked to make a study of the works of these three authorities to discover points of agreement and clarify the subject for the benefit of engineers in general. Requests were made that each of the three authors in question furnish a list of his writings to be considered in this connection. Such lists were received from Mr. Ricardo and Mr. Janeway, but not from Mr. Whatmough in time for use in preparing the original paper. After the paper was delivered, a letter was received from Mr. Whatmough, and revisions in the paper have been made on the basis of that letter. Credit is given to Mr. Ricardo for initiating the study of combustion-chambers and inspiring other workers.

SIX CYLINDERS are used in the Chevrolet engine, because six cylinders give smoother action and a longer range of satisfactory performance than four. Maximum results per dollar has been the ideal in the design, and high output has been secured at a cost very little higher than for a four-cylinder engine. The piston displacement is large enough to give satisfactory performance without fine tuning. The bore is made as large as possible within the space required for water-cooling around the valves. The stroke is short, resulting in low inertia forces and a stiff crankshaft with the minimum amount of metal. Three main bearings are found sufficient, because of the stiffness of the shaft and the inherent balance of the groups of three cylinders. Positive lubrication is provided, without pressure. The overhead-valve mechanism is so proportioned and the cooling of the parts is so arranged that variations in expansion cancel each other and result in nearly constant valve clearance.

COMPARISONS are made of the respective characteristics of the large-bore short-stroke engine and the small-bore long-stroke engine in connection with the argument of the author that the former engine best fulfills the requirement that an engine must be a good product that is easily produced. He chooses the L-head type of engine for purposes of illustration, since this type is within the scope of the experience of all automotive engineers. When consideration is being given the specifications of a new engine, the first problem to be met is the determination of length. Usually a certain length is set arbitrarily, but this circumscribes the designer at the outset and, for some unaccountable reason, a new project is thus compromised rather than to change the preconceived idea of what the length of wheel-base must be.