Historical Notes: Horsepower

Author

A.B.C

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When James Watt first postulated what he considered to be the average power of that four-footed beast of labour that has given its name to work at the rate of 33,000 ft lb. per minute, he had in mind a standard against which he could measure his revised steam-engine against those of his rivals, especially Newcomen. History has often demonstrated that no horse, unless suitably treated with upper-cylinder lubricant or Guinness, can hope to keep up that rate of doing work for much longer than it takes for a modern hydraulic shock-absorber to cease work altogether, a characteristic, as we shall see, shared by some modern motor-car power units, but the spirit was willing, even if the flesh became progressively vain as the steam age gave place to the new era of petrol and alcohol.

Without disrespect to the originator of the unit that we have all come to love however, it may be suggested that he might, had he lived to see the present days, have modified somewhat his values to suit the modern age. Lacking the assistance of Watt himself,  perhaps “A.B.C” might be allowed to venture a few thoughts as to some of the possible modifications that might be made to our ideas as regards horsepower as applied to internal combustion engines, especially such as are fitted to our modern racing and sports cars.

Firstly, it would appear expedient to sub-divide “horses” into three distinct groups. Horses Type A might well be applied most suitably to the first of these groups. Now Horses Type A are of extreme importance in these modern times, and are positively essential if you should want to sell motor cars, especially sports cars, to America. Horse Type A is a fruity quadruped, usually equipped with the full complement of hairy legs, and is normally kept in the stables, to be indented for by the highly-skilled designer, as and when appropriate, to impress the directors (first) and the customers (second). You have, for example, to design an engine to power the great sports car you are going to create, so you look around for a suitable mass-produced unit that someone-else is getting tired of, and then you think of an entirely suitable figure, which you are pleased to call B.M.E.P. (which sounds marvellous anyway), and setting this upon your pocket slide-rule, you rush rapidly through a formula which involves r.p.m. and other unmentionables — and lo ! you have a good supply of Horses Type A.  An order to the publicity department produces the required number, and you print them straight away in the catalogue, thus allowing small boys at Earl’s Court and prospective purchasers in California to say ” Coo ! ” at the earliest possible moment. Now, it may be considered that the foregoing remarks demonstrate that Horses Type A serve no useful purpose. Nothing could be farther from the truth. Apart altogether from the question of fact, their use is psychological, and anyone who knows the army knows the power of  “the trick cyclist.”  Psychologically Horses Type A help to fix other people’s ideas in the right “bracket” and having got them fixed there the recipient of the idea will automatically, especially at the buffet at the local motor-club meeting, make suitable addition of Horses Type A, upwards. This process has even been known to happen at the “Phoenix.”  More than that, motor races have been won on Horses Type A, for who would ever drive a good race if he really believed that his B Type E.R.A. only produced 165 real horsepower ?  Horses Type B that is, of which more anon. Perhaps Mr. Mercedes knew a thing or two about Horses Type A not so long ago, but he obviously used the Italian export type, which may be different.

Unhappily though, there being no justice in the world, Horses Type A have a sad knack of going weak at the knees and failing to place their full weight upon the gin when the day of reckoning comes and the engine actually motors on the test-bed. Horses Type B, on the other hand, are a precious possession and are usually available at the rate of about 2 for each 3 Type A. It is well to remember, however, that they are at their best when they appear at the point where the rear wheels meet the road, as opposed to when they make a brief appearance at the flywheel, as they have an unhappy knack of disappearing en route between these two points and re-appearing as horses Type C.  Two years ago a certain person who used to make Riley motor cars go inordinately fast said to the writer something after this fashion, “If someone has 190 h.p, which is 190 reliable horsepower, and he can drive his motor car, and he is still going at the end, he can still get a place in most modern motor races.” He was referring to Horses Type B — and within limits, he was dead right. Think back to some of the sad Maseratis that trailed pathetically round behind the ” B ” and ” B/C ” Type E.R.A.s not so long ago. Bear in mind that an average ” B” Type had a genuine 165 or 170, and a “B/C ” Type 190 to 195 at best. You might perhaps add another 25 for boring out to 2 litres, but what did Mr. Maserati say?  250 h.p. was it  No wonder one means that bench tests in Italy are done on brakes made by Heenan and “Freud.”

Horses Type B, therefore, our second class of horses, are those that are not only available where they do most good, but go on being available right to the end of the motor race. They are worth precisely 33,000 ft.lb./min. each, as Mr. Joule said they were, as opposed to the 35,000 or upwards of Horses Type A, according to how accurately you adjust your slide-rule. If your modern 10-h.p. motor car has 35 Type B Horses, your 500-c.c racing car 45, your Formula ll effort 140 and your 3-1/2-litre sports car 120, rest very thankful, unless your name happens to be Joe Craig. But to return, we have seen that Type B Horses can sometimes turn themselves rapidly into Type C and when this happens they cease to provide work and appear exclusively as heat, again as Mr. Joule said they would. There are a number of people going around with long faces who might at first sight appear to be those who have been sold Type A Horses and who, upon getting the power unit upon the test-bed, are convinced that Horses Type B just do not exist. Actually, in many cases, they are those poor souls whose Horses Type B appeared for a brief spell but subsequently converted themselves into Type C and disappeared from sight, unless one accepts as visible evidence of their passing a set of exhaust valves vaguely resembling cauliflower ears. It is one of the things that redounds to the discredit of motor racing that enough attention has not been paid to Horses Type C. We owe this to the use of alcohol fuel and in consequence really high consumptions are normal. The comparison between the “tuning” skill required to get a 500 c.c. Norton to perform at around 90 m.p.h. on the Island circuit on “Pool” petrol, and that required to produce 400 h.p. (Type A) or 300 h.p. (Type B) from a highly supercharged 1-1/2-litre engine on alcohol is a comparison no longer looked at properly. This is due to the fact that in the former case the mixture range within which you have to be is much, much narrower than in the latter, as well as to the fact that in the latter case Horses Type may depart down the exhaust pipe without full vaporisation of the fuel (in badly tuned cases), whereas they would create thermal chaos in the motor-cycle case. In addition, but partly, the same thing, each pound of alcohol absorbs some 450 B.T.U. per pound as it vaporises, as against the 135 B.T.U. of petrol. We should therefore raise our bowlers to Messrs. Craig, Harold Willis (whose memory is so revered in this connection) and all those others who deal very firmly with Horses Type C and who therefore produce reliable “steam” from the petrol engine. We are also entitled to show daylight between cranium and headgear to those who do the same thing on alcohol, but beware of the “reputation merchant” in this connection, he is on a relatively easy wicket on alcohol, in two distinct senses!  

Incidentally, if your bowler hat should, upon scrutiny, prove to have been oval-turned “from the solid” on a wood lathe, stand in a moment’s silence to honour those great souls, like Murdoch, who leaving the theory to other people concern themselves with more down-to-earth fitting and assembly, without which the Watts and the Xs (supply your own pet theory man) would be helpless indeed!  To our muttons, however, or more correctly, to our Horses Type C.

If we represent the heat liberated by the burning of a pound of fuel through our engine as 100 parts, then whatever else may or may not happen, we have got to account for that 100 in our heat balance. Without splitting exhaust manifolds we may say that about 30 parts appear at the flywheel as Type B, whilst some 35 parts (Type C) rush past the exhaust valves and subsequent pipework,  and another 35 parts (also Type C) are dealt with and lost via the cooling system. The proportion of Type C to Type B is therefore roughly 2:I. which may help to explain what the genius Carnet wrote in 1824, as touched upon in  “Thermodynamics” two months ago in this series. But the matter goes somewhat deeper than this, unfortunately, in that if we lose a Type B, as our total must still balance, we automatically create a Type C and not only do we fail to motor forward so quickly to the tune of the missing h.p. but we also have an additional “horsepower’s worth” of heat left over to play hell with the exhaust and cooling system, to say nothing of the cylinder head and gasket.

Equally, of course, if we gain a Horse Type B we destroy automatically a Type C to correspond, which means that we are faster and thermally more reliable. Thus do Horses Type B and C interchange themselves, a double loss or gain as the case may be. Efficiency, therefore, is just about twice as important as some people imagine. “Casque” who used to make us laugh (and still does) when he drew us a picture of the team chief showing the motoring correspondent a blown gasket as an excuse for his motor car’s retirement, was nearer the truth than some knew.

The real joke was that a blown gasket, far from being the ”bad luck” that served as the excuse to the public, was actually a public confession of the allowing of Horses Type C to abound, a far worse state of affairs than the broken crankshaft which was the “real” trouble!   Touching further upon Horses Type C there is also the important fact that they take a moment or two to show themselves on the test bed. For example, your powerful racing engine may fly up to giddy outputs but these outputs have a tragic habit of dropping off after a short space of time as the B’s and C’s interchange. How different are sustained outputs and “flash” readings is another lesson that present-day racing has failed to teach us. Brooklands and the like, yes, but Silverstone and Goodwood, no.  How often as youthful enthusiasts we pour scorn upon other than racing engines. Oil engines—pooh!, a mere 20 b.h.p. per litre, how poor compared with the 150 b.h.p. per litre of the blown “750” of the ‘thirties. The real difference in performance between the racing and the industrial engine is certainly not as great as some people would have us imagine, especially if length of life is borne in mind. It is sometimes profitable to re-read history with that in mind. To take a typical example, a well-known eight-cylindered power unit is reputed to give over 90 b.h.p. according to the maker’s curves, but will certainly show signs of distress if asked to maintain 60 for an hour on end, and 40 to 45 is about right for really continuous operation. Most other motor-car power units would show proportional figures.

What saves us in the motoring world is that we can seldom, even on a fast run, hold the load factor really high for more than a few fleeting seconds and further, the faster the motor car the more fleeting the opportunities are.

But this is the season of good will, so let us wish to all those who aspire to motor racing in the new year “God Speed,” and the maximum number of Horses Type B. May the discrepancy between the quantity of Type A and Type B for a given engine be more than made good by the driving skill of the “pilote” and finally, may everyone be spared the conversion of an undue number of Type B into Type C and the attendant document that usually commences “To stripping down, cleaning and inspecting etc., etc.  —  A.B.C.

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