Towards the end of 1912, there appeared in the Autocar a series of articles of more than usual technical interest. Their subject matter, which concerned the relative merits of 90 by 120 mm. and 80 by 150 mm. as dimensions for a 3-litre engine, would in itself have been sufficiently enthralling for those who are capable of being enthralled by technicalities of automobile engine design; but when it is added that the protagonists in the discussion were, on the one hand, Laurence Pomeroy senior, the designer of the “A”-type 90 by 120-mm. Vauxhall, which proved such an outstanding success in the R.A.C. 2,000 Miles Trial of 1908 that it made its designer famous overnight, and, on the other, Louis Coatalen, who was responsible for the 80 by 150-mm., 12/16-h.p. Sunbeam; which in modified form had just swept the board in the Coupe de l’Auto, thus scoring the first British win in a big Continental race since S. F. Edge captured the Gordon Bennett Cup a decade before, it will be seen that the articles probably held the attention even of those readers who normally passed over such matter in order to hurry on to the small advertisements.
As a matter of fact, the whole thing had started the previous year, when Pomeroy had contributed an article, in which he put forward the argument that the then universally popular engine of 80 by 120 mm. bore and stroke (2,402 c.c.) was too small as an adequate power unit to propel a chassis with a full 5-seater body, as it was commonly required to do. From the figures with which he supported his contention, I should say that it was a powerful one — more powerful, one is tempted to remark, than the engines in question. But as to the popularity of the type, there can be no question. Argyll, Berliet, Charron, Crossley, Darracq, Delahaye, F.N., Hotchkiss, Imperia, Martini, Mors, Motobloc, Panhard et Levassor, Piccard-Pictet, Renault, Roper-Corbett, Th. Schneider, Star, Talbot, Unic and Vulcan all offered models with these engine dimensions for the 1912 season. According to Pomeroy, the motive which actuated these manufacturers was the desire to provide “something of about 15 h.p.” and to pretend that it was fit for a job which was really too big for it. But as he himself remarks, the majority of the offending makers were of foreign extraction, and although the English market was admittedly of considerable importance to them in those free-trade days, I find it rather hard to believe that such a very large number of them were prepared to risk their reputation simply in order to satisfy the idiosyncracies of the British taxation system.
Besides, I have yet to be convinced that there was anything inherently wrong with the 80 by 120-mm. engine. The fault obviously lay not so much in building too small an engine, but in burdening it with excessive top-hamper at the coach-builders. If, in 1912, Peugeot could so much as hope that the engine of the 855-c.c. “Baby” was capable of moving a motor-car at all, then surely 2,400 c.c. should have been able to propel a reasonably light one pretty effectively. And as to a bore and stroke of 80 by 120 mm., it seems to me, as I have already suggested, rash to assume that they owed their origin, at least in all cases, to impecunious or parsimonious British buyers with an eye to the tax question. There was, on the contrary, long tradition behind those dimensions, a tradition which reached back to the original 2-cylinder Phénix engine fitted to the 4-h.p. Panhard et Levassor, with which, as long ago as 1895, Levassor won the “Paris-Bordeaux-Paris,” the first motor race ever run. In its 4-cylinder form, the 8-h.p., still with the same dimensions, was the power unit with which Mayade won the “Paris-Marseilles-Paris” the next year, and with which Charron was victorious in the first inter-country contest, “Paris-Amsterdam” of 1898. I do not think that any historian could fairly claim that, if Panhard et Levassor, at any rate, were building an 80 by 120-mm. engine in 1911, their choice of these dimensions was determined solely by the taxation system in vogue on this side of the Channel.
Pomeroy, in any case, advocated in his article the retention of the 120-mm. stroke, but an increase in the bore to 90 mm, which would bring the capacity up to 3,044 c.c. Alas! his voice was as of one that crieth in the wilderness. Not for nothing had the organisers of the French voiturette race decided in 1907 to limit the bore of engines and allow designers a free hand with the stroke. Not for nothing had the A.C.F., as far as the Grand Prix was concerned, followed their example in 1908, or the R.A.C. organised the “Four-Inch” Race. Laurence Pomeroy himself had remained unperturbed: The “A”-type Vauxhall of 1908 was developed into the original 3-litre “Prince Henry” of 1910, which developed 60 h.p. and attained a speed of 100 m.p.h., and for the 1911 Coupe de l’Auto no further modification was made in the Vauxhall engine dimensions than to clip 2 mm. off the stroke in order to bring the capacity actually within the 3-litre limit. But with practically all other designers the long-stroke engine had become the vogue, and it was the stroke that they decided to increase, not the bore.
So much was this the case, that when it was decided in 1911 to abandon the maximum bore regulation for the Coupe de l’Auto race in favour of a 3-litre capacity limit, it was considered desirable at the same time to fix a maximum strokebore ratio of 2 to 1. Peugeot, whose racing department was run as an entirely separate entity to the production side, immediately built engines right up to the permitted limit, with dimensions of 78 by 156 mm. Adage, not having a 3-litre model in production, was equally uninhibited, but decided to stick to a “tidy” bore, and chose 80 by 149 mm. These cars proved by far the most successful in the race, taking first, third and fourth places, with Georges Boillot’s Peugeot second. They were followed home by a Grégoire, which, having a standard model of 80 by 160 mm., had met the capacity limit by reducing the stroke, reluctantly one presumes, to the same length as that of the Delage, and a Calthorpe, whose makers had refused to shorten the stroke of the standard 80 by 150-mm. engine, but had restricted the bore by half a millimetre instead. Then came two Arrol-Johnstons using the standard 80 by 140-mm. engine and not up, therefore, to the capacity limit; another Grégoire; a 2-stroke Cote, which we can hardly include in this discussion; the third Arrol-Johnston; and finally the car with the shortest stroke among the finishers — an Excelsior with engine dimensions of 85 by 130 mm., half way, that is, between the Delage and the Vauxhall. If racing proves anything, the race seemed to be a complete vindication of the long stroke.
Subsequent results seemed for a time only to confirm the lessons of 1911. Delage was an absentee from the race in 1912, and no 3-litre Peugeot finished; but, as has been mentioned, three Sunbeams, with the same engine dimensions as the 1911 Delages, scored a grand slam victory, and were followed by a Th. Schneider and an Arrol-Johnston, both with engines of 80 by 140 mm., and each of which beat Durily’s 85 by 132-mm. Alcyon, which in its turn beat Vonlatum’s 89 by 120-mm. Vinot et Déguingand. There are indications that the 90 by 118-mm. Vauxhalls were the fastest 3-litre cars in the race — Hancock having led for the first 240 miles — but none of the team finished. And in 1913, the engine dimensions of the three makes being still the same, the order at the finish was Peugeot, Peugeot, Sunbeam, Vauxhall.
At this point I should like to quote at very considerable length from the long versus short-stroke protagonists, to whose articles I started by referring, because, in spite of the lessons which racing seemed to teach in these years, careful consideration of the arguments put forward must, I think, incline any impartial critic heavily in favour of Pomeroy. (He was, of course, to be proved right in time; the trouble with him, as with many men of genius, was that he was before it.) But, as each of the three articles, two by Pomeroy, one by Coatalen, is as long as the whole of this effusion may be, I am afraid that I shall be able to do neither designer justice.
Briefly, however, Pomeroy starts off with the statement which, he says, will be, to the technical reader, axiomatic, that the maximum power developed by an engine must be a function of three factors: cylinder capacity, mean effective pressure, and crankshaft speed. Since he is discussing the optimum dimensions for a 3-litre engine, the first of these can obviously be disregarded. As to the second, theory suggests that the smaller the bore, the greater the cooling influence on the mixture caused by the proximity of the cylinder walls, and consequently the lower the m.e.p.; but practice, according to Pomeroy, shows that actually this factor does not make two ha’porth of difference. The third, on which, of course, one would expect a short-stroke enthusiast to dilate, since the shorter the stroke, the higher the ratio of crankshaft to piston speed, he also, curiously enough, dismisses in most summary fashion; but then he is discussing touring car engines, and for them, evidently, he considered a crankshaft speed of 2,000 r.p.m. as high as was desirable. And he therefore comes to the conclusion that, as far as maximum power is concerned, there is nothing in it between 98 by 98 mm. and 80 by 150 mm.
But on other counts there is a lot. First, at low engine speeds, say between 400 and 1,000 r.p.m., the cooling effect on the mixture of the cylinder walls does begin to have a noticeable effect on m.e.p., and the big-bore engine scores as a “slogger” every time. (Was it — perish the thought! — this aspect of the matter that finally attracted General Motors towards Luton? At any rate, one cannot think that the purchasers of “Prince Henrys” attached much importance to it.) Second, the shorter the stroke, the shorter the crank-throws, the stiffer the crankshaft and, therefore, clearly, the higher the measure of reliability and durability which might be expected from the engine. Against this claim Coatalen, very reasonably as it seems to me, appealed to the actual results of racing: the 1912 Grand Prix was over a distance of 956 miles and the leading Sunbeam averaged over 65 m.p.h. Third, the short-stroke engine will be lighter. This contention is, I think, incontrovertible, because although the small-diameter pistons of the long-stroke will be lighter, this is almost certain to be offset by the larger crankcase and the heavier crankshaft which will have to be used. In one respect, however, Pomeroy perhaps overstated his case. There will, he said, be little or no saving in the weight of the cylinder block on account of the smaller bore, because, in order to aspire the same volume of gas, the valve area will have to be the same in both engines, and both, therefore, will have to be of equal length. Now this, if I may say so without disrespect, was an L-headed remark; for it is only true on the assumption that the valve arrangement is also similar. As between the Vauxhall and the Sunbeam the comparison was a fair one; but I think the author might have mentioned the fact that the 1895 Panhard, with its overhead automatic inlet valve, could have sucked its whole cylinder head off, if it liked, each induction stroke, and that the same applied, more or less, to the mechanically-operated overhead inlet valve Sizaire et Naudin which won the early Coupe de l’Auto races.
The victorious 1910 Hispano-Suiza had achieved large valves with a bore of only 65 mm. by using a T-head, the 1911 Delage had arranged its valves horizontally, and the Peugeot designers were using inclined overhead valves with two overhead camshafts — arrangements all of which probably involved more weight than a simple L-head, but which had other, and perhaps compensating, advantages. But apart from such quibbles, Pomeroy, by and large, was clearly right; once you introduce a weight limit, the long-stroke engine seems to go by the board.
Louis Coatalen, however, was an addict of the long-stroke with all the enthusiasm of the convert. Born in France in 1879, he had come to England in about 1900, and spent the early years of the century with the Humber Company. Thence he had gone into partnership with William Hillman in time to build the Hillman-Coatalen cars for the 1908 “Four-Inch” Race. With the maximum bore of 101.6 mm., their engines had one of the shortest strokes in the race — 127 mm., which, being interpreted, is, I suppose, five inches. And the standard model, from which this was developed, had a “square” engine of 5 in. bore and stroke. The Humbers, which were among the fastest cars in the race, had an engine stroke of 150 mm., the stroke of the winning Hutton was 180 mm., and it was followed in by two 160-mm. Darracqs. Coatalen finished, but he was a full 10 m.p.h. slower than the winner. For speed, evidently, the stroke should have been longer. But perhaps Hillman did not like long strokes — until 1913 the company continued to build the “square” engine of 5 in. bore and stroke, and it was only then that it went to the other extreme and produced a 60 by 120-mm. model, with stroke-bore ratio of a full 2 to 1. In any case, the Hillman-Coatalen partnership did not last, and in about 1909 the latter moved on to Sunbeams. The result was the 12-16-h.p. model, which, in the guise of the 16-40-h.p. with overhead valves, lasted on until 1923.
By 1912 Coatalen could comfortably counter most of Pomeroy’s theoretical arguments by an appeal to results; for if the latter designer was one of the most brilliant that this country has ever produced, he was also without question one of the unluckiest. On the theoretical side, I do not feel competent to judge whether there was in fact any force in Coatalen’s argument, which Pomeroy discounted, that while admittedly the long-stroke engine’s connecting-rod had to be longer, it could be made lighter in relation to its length, because the explosion pressure, being distributed over a smaller area, exerted a less violent effect upon the moving parts. When, however, he went on to argue that in consequence the transmission could safely be made lighter, I think that, as Pomeroy pointed out, he was clearly in the wrong, because once the fly-wheel had converted the explosion impulses into torque, it was this resultant torque and nothing else with which the transmission had to deal.
But while logic and the test of time have decided in favour of the short stroke and against the long, I cannot but regret the passing of the latter. There was a certain ineffable charm about the long-stroke engine of 1912 which it appears impossible to recapture with the modern power unit, however much greater may be its efficiency. The prime exemplar of the former, of course, is the “Alfonso” Hispano-Suiza. Developed from the 65 by 200-min.. racing voiturette design, this 80-mm. bore engine had a stroke of 180 mm., instead of the mere 150 mm. which the Sunbeam boasted. And its characteristic quality I can only attempt to define by the word “courage.” This is not what the French call a nervous engine — its acceleration, by any modern standard, is poor. Moreover its designer, Marc Birkigt, was never one to gear an engine unduly low. But take an “Alfonso” across country in company with a more modern car, and you will find that while you are left standing when it comes to accelerating out of a bend, a long trying hill which will wear down your opponent will be tackled by “Alfonso” in his peculiar indomitable manner, and as you breast the top of it, you will have regained all those seconds which seemed irretrievably lost at the corner at the bottom. I wonder whether this is just a question of litres, or whether the contemporary 70 by 170-mm., 4-cylinder Sizaire-Naudin, with the smaller capacity of 2,610 c.c., but even higher stroke-bore ratio, had similar characteristics? If so, were they still more apparent in “Alfonso’s” prototype, the 65 by 200-mm. (2,646 c.c.) engine? If the answer is in the affirmative, then there is surely an a fortiori argument in favour of Georges Boillot’s 4-cylinder Peugeot which ran in the same race and which had engine dimensions of 65 by 260 mm.; giving a capacity of 3,440 c.c., nearly equal to the “Alfonso’s” 3,600 c.c. This must have been a most remarkable vehicle, and I cannot quite think why it did not win the race — it apparently overheated rather badly, which was a point, incidentally, which Pomeroy made against the long-stroke engine. Coatalen, as with so many other of Pomeroy’s points, was able to counter it successfully by appealing to experience, as far as a stroke of 150 mm. was concerned. But with a figure as high as 260 mm. it may have declared itself in practice as well as in theory.
To return to the 1910 4-cylinder Peugeot, it was designed, so I am assured on impeccable authority, by Ettore Bugatti, who arranged its cylinders in V-formation, so as to reduce the height of the engine, and then added to this dimension by giving it an overhead camshaft, driven by a vertical shaft. There were four valves per cylinder, the intakes being vertical and the exhausts horizontal, and final drive was by side chains, as in the case of “Black Bess.” A motorcar, one imagines, with a pretty dynamic performance — when it was not stopping for water. But as no one seems prepared to present me with one like it, or with a contemporary racing Hispano, or even with a sports model 4-cylinder Sizaire, my estimates of the performances of all of them must, it would seem, remain the products of my long-stroke — and perhaps overheated — imagination.
[This instalment of “Sideslips” is particularly interesting to owners of 80-bore Edwardians, such as “12/16” Sunbeams or “Alfonso” Hispano-Suizas. The pleasure of restoring and running an early car is greatly enhanced by discovering how one’s particular example fits into history, and “Baladeur” raises some items of especial interest in this connection by recalling the great significance which bore and stroke/bore dimensions had in Edwardian times. — Ed.]