SIX-CYLINDER ENGINES.

Putaruru Press, 19 January 1928, Page 7

SIX-CYLINDER ENGINES.

SMOOTH-RUNNING CARS. Higher Petrol Consumption. No discussion of motoring topics to-day proceeds very far before it turns towards the six-cylinder engine, writes the Autocar. The type is the limelight, and its virtues are the subject of close attention. Interest is directed particularly towards the sizes from 10 to 16 nominal h.p., in capacity between 1000 and 2000 c.c., for such engines are now being put into the modernised four-five-seater touring cars by progressive manufacturers.

As a power unit for a car the sixcylinder engine is not a new proposition at all; it has been in use for well over twenty years. But between the large capacity slow-run-ning six of bygone times and the small high-speed six of to-day there is a vast difference, a difference so complete as to necessitate a rearrangement of ideas. It is with the idea of taking stock of six-cylinder design, particularly in regard to gas distribution, with which a great deal of trouble is being encountered at present, that this article has been written. But right at the outset it seems necessary to make it quite plain that no adverse criticism of the small six-cylinder engine per se is intended, the actual inspiration being a desire to see the type developed further towards the full extent of its possibilities. Virtues of the Six. In the past, when a six was made to take the place of a four in a car of given carrying capabilities, it was usually given a considerably greater total cylinder capacity than the four, because it was a longer and heavier engine. The chassis also became heavier, as it had to be lengthened to make room for the longer engine without encroaching upon the body space. Thereafter these comparatively large six-cylinder engines were seldom asked to work right up against the collar. Hence, if there were difficulties incidental to sixcylinder designs, they were not initially brought into special prominence; but, when modem development starts on another tack and sets about making a small six do work that not so very long ago was a burden to a fairly large four, difficulties at once crop up. Excellent though the small six may be at the present time, as a type it is still inclined to be coy and backward in showing in practice the advantages over the four-cylinder designs with which it is credited by the text books.

Theoretically the six-cylinder engine possesses characteristically a smoother torque, six small overlapping impulses in two revolutions instead of four larger separate impulses, a more perfect mechanical balance, less vibration by reason of lighter reciprocating parts, a wider range of speed combined with the ability, to produce smooth power at slow speeds because of the more even turning movement, and the ability to run at a high maximum speed because of the lessened inertia of the lighter reciprocating parts. This summing up of six-cylinder virtues is not, let it be clear, an attempt to take sides in the evergreen controversy of six versus four. Comparison with the Four.

j Engineers know quite well that, theoretically, the four is entitled to : claim the higher absolute efficiency—j power produced for fuel consumed—since the heat losses and internal ! friction are less. On the other hand, ! it is known also that the six can be ! made to produce more power for its capacity—at the expense of a greater consumption of fuel—because its lighter reciprocating parts and r values permit a higher rate of revolution. More power can be poured out because more fuel can be poured in, . but only by making the engine run faster.

When it is proposed to replace a first-class four-cylinder engine by a first-class six of the same capacity, the all-round demand made upon the latter is exceptionally severe. For salesmanship reasons it has to be a better engine than the four in ways that are immediately obvious when the car is tried by the man in the street. Being a six, it is expected by the average man to be smoother running at all speeds/ more flexible and capable of pulling evenly at a very slow speed on top gMr, yet at the v same time its liveliness and capabilities of speed on the road must be ' at least equal to those of the four, if not; better.