The above question, upon which I have been asked to write a few notes, is so broad and general that it is quite impossible to return a simple direct answer to it. If it had been “Will the super charger benefit some types of touring car ? “I should perhaps have been able to be more definite.
On the other hand, if it had been” Will the super charger benefit all touring cars ? ” I would by no means commit myself in its favour to this extent. It is very easy in a matter of this sort, unwittingly, to give the impression that any principle which one may advocate for certain conditions is desirable for universal application, therefore I wish to make it clear at once that the use of a super charger on the ordinary general utility type of touring car, in which first cost is naturally an item of great importance, is a very remote possibility indeed, and very far from a probability.
It should be borne in mind that there is no strict dividing line between the racing car and the touring vehicle, inasmuch as there are so many gradations of the latter. For instance, the highly developed ” sport ” or ” speed” model (a type which is steadily increasing in popularity) is neither more nor less than a racing car in which certain concessions have had to be made to accommodation, ease of upkeep, quietness and comfort.
A little further along the scale one finds that more and more concessions are made with an accompanying further sacrifice of speed and acceleration, combined with an increase in weight. Further along still one comes to the sort of car which is just simply mechanical transport.
In this sort of vehicle vitality is of no consideration whatever, the only qualities demanded being cheapness, reliability, and reasonable comfort. Thus it happens that a mechanical device which in one sort of ” touring ” car might be a very desirable thing indeed, would in another ” touring ” car be an unnecessary luxury and complication, and in yet a third ” touring ” car, nothing but an unmitigated nuisance.
It is because of these facts that one can rarely answer a broad question such as the above, in a direct and unqualified manner. To be precise, I confess I have some hesitation about answering it at all, having regard to the need for having a very lengthy experience of any engineering contrivance before making up one’s mind about it ; my own view is, however, that for certain types of touring car, the super charger principle has distinct possibilities:
The great advantage of the super charger is that it enables such a valuable amount of extra power to be got out of an engine, that is both small in size and light in weight. It does this by virtue of its ability to fill the cylinders with a greater weight of gas than would be possible with the ordinary induction system operating under atmospheric pressure.
Many people have the idea that, in consequence of this action, the super charger is really only of substantial advantage at the top end of the revolution scale, at which point maximum power is being obtained, but the actual scope and value of the device goes a great deal further than that.
By means of experiments carried out in the Sunbeam two-litre engines, built for the Grand Prix, I have been able to show that, whilst the super charger adds very pronouncedly to the power at high revolutions—the increase under favourable conditions being something in the neighbourhood of fifty per cent.—its benefits are even more marked at lower speeds.
When seeking after high power from an engine of limited size, it is necessary to concentrate upon high effective revolutions. To attain this object involves the use of fairly large valves provided with a pretty big lift, otherwise there would be wire-drawing of the gas and the horse power curve instead of rising or even continuing flat would fall off long before the speeds aimed at had been attained.
Now at lower speeds it is found that the big area of opening made possible by these valves, combined, of course, with the necessarily early timing of the valve mechanism, results in very uneven running. This is due partially to disturbance of distribution and partially to an absence of that turbulence in the gas which has been shown to be of such importance in an internal combustion engine.
Thus it not infrequently happens that an engine, designed to run and to give maximum power at, say, 6,000 r.p.m., with scarcely any pull at all at less than 2,750 r.p.m., and I need hardly say that this implies a very strenuous use of the gear box.
When one applies a super charger to this sort of motor, these disadvantages immediately disappear, and there is a perfectly enormous increase of torque at the lower revolutions, accompanied by a consistent regularity of torque, thanks to the neutralisation of distribution troubles.
The result is that the top gear performance of the car is conspicuously bettered, for not only is more power and therefore more acceleration available, but these benefits cover a much wider useful scale of revolutions.
In the meantime the super charger has itself absorbed a considerable amount of power on its own account, for it is a pumping mechanism which has to do a great deal of work, but its effect is such that the power lost in this way is quite small compared to the extra power which is introduced.
On many occasions it has been suggested that the use of super chargers on motor cars has been definitely brought about solely by the restriction of cylinder capacity in the more important races, and that had this restriction not been in evidence, designers would simply have made their motors of larger capacity.
It is thus sought to be established that the super charger is no better in any way than an increase in cylinder dimensions. That, however, is not quite true
There has for years been a 6teady and an absolutely justifiable tendency to multiply the number of cylinders and to make each individual cylinder smaller in dimensions. This tendency exists altogether apart from any considerations of taxation, for it is manifest on the other side of the Atlantic, where car taxes are happily trivial, as well as in Great Britain, where they are absurdly high.
There are very good reasons for this state of affairs. One is that in the small multi-cylinder one has a means of reducing the stresses on the vital working parts, another is that one gets greater uniformity of torque, which implies greater comfort to the passengers and less wear and tear on the transmission.
A third is that one gets a reduction in size and in weight of the power plant, which in turn means a less bulky, a more economical and, at the same time, a stronger vehicle.
To my mind, the super charger system has great possibilities, inasmuch as it helps forward the tendency to which I have referred, that is to say, for a given power, it makes smaller and smaller engines possible, so that if not in principle, at least in effect, one begins to approach the internal combustion turbine which has so long been looked forward to in vain.
These advantages do not accrue from a mere increase in the size of an engine, although that may well be the cheapest method of obtaining a desired increase in power. We want, however, not alone more power, but a more uniform flow of power. Also we want lighter, more controllable, more durable, stronger, livelier and more economical cars.
The merely larger engine does not accomplish these objects and its adoption would therefore be a retrograde step.
As to the super charger, it cannot be pretended that it is without disadvantages. It is not cheap to make, for it requires to be very efficient if it is to do any good at all ; the problem of its silence presents certain difficulties ; it cannot be denied that it is a complication (though a complication is not necessarily disadvantageous) ; finally, because it has a lot of work to do, it gets hot and therefore some means must be devised for keeping it adequately cool.
In view of the fact that the super charger for motor cars is as yet in its very early stages of development, it would be absurd to suggest that these difficulties are insuperable, even regarded as an aspect of touring car design. In this connection we must bear in mind that the super charger is a component, which by itself is of the utmost simplicity, having nothing but a plain rotary motion and having, therefore, an inherently perfect balance.
All these considerations point to the possibility of the super charger being ultimately able to establish its utility in connection with that type of car in which a really good performance is called for. In a racing car, of course, one is aiming at maximum performance, irrespective of anything else.
As an example, the two-litre supercharged Sunbeam engine gives well over 160 b.h.p. It could be considerably ” detuned ” and it would still give 100 b.h.p. over quite a large scale of revolutions. This fact in itself suggests possibilities which may at length be realised.
In the meantime it may be remarked that much has been said and written about the value of racing. In my opinion racing would be justified if it has done nothing else than bring the super charger principle into the limelight, from which I have little doubt it will finally emerge (as so many other racing ideas have done in the past) as something of distinct importance in touring car design.