STILL SMALLER SIXES.

New Zealand Herald, Volume LXVII, Issue 20538, 12 April 1930, Page 12 (Supplement)

STILL SMALLER SIXES.

AN INTERESTING POSSIBILITY

'ADVANCES IN" DESIGN.

Seven and eight horse-power cars with miniature saloon bodies arc an entirely British product, and so exceedingly successful have they been that they have como in for a great deal of discussion. One of the topics of speculation to-day, sinco the present crazo is for "light sixes,'' is tho possibility of their development with six-cylinder instead of four-cylinder power units. Tho subject is an interesting one, because in the fullness of time tho tiny six-cylinder car will undoubtedly become an accomplished fact, though at the present juncture there, ara considerable difficulties in the way of its rapid evolution. Small sixes are already in existence; but either they are sports cars or else they hardly fall within the miniature class as regards the size of tho body. It would seem that the true miniature car enthusiast does not want a larger car with a six-cylinder engine, but a car of the saino sizo with moro cylinders, to give him a better road performance, with the least possible increase in running expense. Such a car as this is quite practicable, but only provided that tho owner will not expect a 50 per cent, increase of speed when he has his four-cylinder engine mado 50 per cent larger by the addition of two more cylinders.

" Tho outstanding difficulty of producing the desired car is mainly tiiat of ing efficiency. It is well known that for sheer efficiency a six-cylinder engine falls short *i a four-cylinder of an equivalent size, and by tho word efficiency is meant the power developed from a unit of fuel. Tho reasons are that the heat losses in tho six aro greater, and so also are the frictional losses. But in addition, a very marked difficulty _ arises with a six, that of the distribution of equal quantities of homogeneous gas mixturo to each of tho cylinders. As tho sizo and capacity of the engineare decreased this difficulty tends to increase. No one questions that tho six-cylinder engino can be made much more pleasant to drive behind than a four, because of tho smoother torque. By running at higher speed tho six can givo moro power than a four of the same capacity, and tho lower inertia forces of its light reciprocating parts permit increased revolutions. But the economy is less, and also, since the best cannot be obtained from a six without perfect distribution, tho need arises of a method _ of feeding tho gas mixture into the cylinders in a manner perhaps of tho super-charger. Is is this need of obtaining maximum power with tho aid of maximum revolutions that causes racing cars to uso_ supercharged six or eight-cylinder engines. So far as tho"" miniature six-cylinder is concerned it would seem, then, that tho first obvious step would be to add two more cylinders of the same size to an existing four-cylinder engine and chassis which is an attractive manufacturing proposition, to stretch out tho wheel-base of the car enough to accommodate tho extra length of tho engine, and then to carry on with the samo range of coaclnvork for tho six as for tho four, which is another even more attractivo manufacturing proposition. But the car so produced wsuld in nil probability be very little faster than tho four-cylinder, though it should bo smoother and more pleasant. Six cylinders instead of four mean, broadly, 50 per cent, greater heat losses, and 50 per cent, more friction in the engine; henco the available horse-power, without an increase in speed of revolution, would not be 50 per cent, greater. An attempt to increase the speed revolution would necessitate a relative increase in induction pipe and carburettor size, and this again makes distribution more difficult if there is to be no sacrifice of flexibility at low speeds, whereas tho public expect more and not less flexibility from a six. So one might expect to find a car with ifs weight increased, yet with only a small increase in power, and therefore with only a slight improvement In general road performance. Possible Developments.

It would seem more likely therefore that eventual development will proceed along the lines of evolving a six of the same size as the four, but propelled bv an engine of altogether higher efficiency than is at present possible in normal touring practice, and the obvious method of achieving this is by supercharging. It will be understood that these comments are made in the light of present knowledge, for it would bo a bold man who would state that no improvement is possible which might entirely revolutionise present-day practice. Indeed, such improvement may bo imminent. The key of the situation is gas distribution. Engines of higher efficiency may entail a loss of reliability but tin's is an obstacle by no means insuperable, though the solution is usually increased cost of manufacture in the initial stages of development. It is rather interesting to forestall the march of tinrj Tud visualise the possible appearance of. n famous small car converted into "'light sixes." The extra length of the engine would entail a slightly longer wheelbase, and it is remarkable what a difference this would effect in the appearance, considering that the bodywork has not been altered. Continuing to explore the field of speculation, various surmises can be made regarding tjie possible porformanco on the road. In the first place, even this slight increase in tho wheelbase should effect an improvement in tho spring suspension, chiefly in tho direction of damping more quickly any tendency of tho car to pitch fore-and-aft when traversing series of pot-holes. Then the capabilities of the engine to run at an increased speed makes it possible to use slightly lower gear ratios, and these should allow greater flexibility and an improved acceleration on top gear, hence the car might bo a shade easier to drive. As to the possibilities of prico, tho ii)crnnso over an existing small four might not perhaps be very great, provided that tho same rango of bodywork could bo used, and that tho engine had two more cylinders of the sarno size as tho four, so that the same piston, connecting rods, valves, and so forth, could bo employed.