The Need for Speed - Cracking The 100 Mile-Per-Hour Barrier

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The Need For Speed - Cracking The 100 Mile-Per-Hour Barrier


The Flying Kilometre



In 1904 a French racing motorist roared over a flying kilometre near Ostend at 103.56 m.p.h. His 16.7-litre Gobron-Brillie boasted a four cylinder engine of extraordinary design. Less than fifty years later - in 1953 - John N. Cooper averaged 105.7 miles-per-hour over 50 kilometres in a Cooper Special, powered by a tiny 344 c.c. single cylinder engine. In other words, at the infancy of the motor-sports era it took four cylinders and 16,700 c.c.'s to achieve the magic "ton", and just half a century later an engine one fiftieth the size was capable of both reaching and sustaining 100 miles-per-hour.

The analogy can be taken further by showing the progress of an engine of fixed size. The first man to reach the ton with a 1.5-litre engine was J. A. Joyce. He drove a four-cylinder A.C. special at 102.92 miles-per-hour over a flying kilometre during October, 1922. In August 1957, Stirling Moss ran an M.G. special on the Bonneville Flats, Utah, and established an entirely new set of 1.5-litre records, including 245 miles-per-hour for the flying mile. Even more extraordinary was the fact that the engine in question was basically the "B" series power unit then being used in such British cars as the Austin, Morris, M.G. and Wolseley.

Cracking the "Magic Ton"



To get a clear picture just how quickly designers had improved engine design and diminished the dimensions over the first half of the 20th Century, it is best to follow the progress of the pioneer motorists who cracked the magic "ton". First, as you no-doubt know from reading other articles here on Unique Cars and Parts, was Rigolly in his massive 16.7 litre Gobron-Brillie. Six years later - in 1910 - A. J. Hancock drove a four cylinder 3-litre Vauxhall at an average speed of 100.093 miles-per-hour for a half mile of the Brooklands track. The margin of power was so slim that after preliminary attempts failed to reach 100 miles-per-hour, Hancock drained the oil out of the rear axle and gearbox to reduce drag. Then for the first time ever a 3-litre vehicle cracked the ton.

By 1922 far smaller engines were regularly lapping race circuits at a three-figure speed but it took J. A. Joyce's A.C. to be the first 11-litre car to clock 102 m.p.h. Then in 1926, A. Morel reached 122.67 with a six-cylinder supercharged Amilcar of one litre capacity. It was staggering news in its day, as the class record had stood at 78.96 miles-per-hour before Morel streaked over a measured mile at Arpajon. Once a single litre could be equated to 100 m.p.h., further strides failed to make headlines. Not many people took much notice of L. Cushman when he drove a diminutive 750 c.c. Austin Seven at 102.28 m.p.h. in 1931 (also see The Austin 7 in Motorsport).

1906 Itala 4 Cylinder Engine
1906 Four Cylinder Itala engine, with a 14.5 litre capacity and 100+ miles per hour top speed.

Mercedes record breaking Silver Arrow
Mercedes record breaking Silver Arrow.

John Cooper Single Cylinder 100 Miles Per Hour Record Breaker
You may laugh at the trend for 2 or 3 cylinder engines, as used by Fiat, Suzuki and Volkswagen, however John Cooper drove the above single-cylinder 344cc car at 105.71 miles per hour in 1953. Such a speed once needed 16.7 litres.

1958 Renault Shooting-Star
1958 Renault "Shooting-Star", which developed 275 bhp and weighed only 225 pounds / 102 kg.

John Cooper



There was also the extraordinary effort of John Cooper in reaching the magic ton with a 344 c.c. engine in 1953, which according to latter motoring historians had little news impact, that it was virtually forgotten soon after. While we would like to think that modern day buyers of a Mini Cooper, or Cooper Works, understand the heritage to which their car belongs - we doubt it. If those buyers looked back, they could trace the progress of the auto engine by the speeds achieved in each era. The first really fast cars were the giants of the pre-1910 days. There was the massive 1903 V8 Darracq for example, with engine capacity of 22.5 litres. A monster racing Fiat of the same year had an o.h.v. design engine of 16.5 litres and the Itala which won Brescia in 1905 (at 70 m.p.h.) sported a 16-litre engine.

In 1906 most of the European manufacturers were still producing massive racing engines but the turn of the tide came at the French Grand Prix when a 12-litre Renault snatched victory from several giant 19.5 litre machines. The speeds during this event were the highest ever, and because neither the brakes nor the road-holding could match the cars' velocity, the authorities became increasingly concerned with safety - the first time such concerns were ever raised in the days of early motorsport. For the 1907 G.P. the weight limit which had governed previous races was lifted and instead the organisers insisted that all cars competing should be capable of achieving at least 9.4 m.p.g. This new rule failed to achieve anything like the desired result, because Renault had already shown the way to produce greater-efficiency from existing engines, and race speeds proved as fast as ever.

For 1903 they the motorsport governing body decided to limit engine sizes by restricting the bore limits. Once again the manufacturers resorted to ridiculous designs, with enormous strokes and the whole situation developed into such a fiasco that De Dietrich even entered a car with a stroke of 190 mm. Mercedes eventualy won the race (witlh a stroke of 170 mm.) and three Benz cars ran them a close second. Somewhat annoyed at the German success, the French motor industry appealed to the Automobile Club of France and for the 1909 French G.P. the bore limit was reduced once again. Further confusion followed and eventually so many manufacturers withdrew that the race was abandoned. Nevertheless the curtailment of bore sizes did much to bring manufacturers to their senses. Faced with the prospect of producing more power from smaller engines they began - for the first time - to make serious studies of combustion and valve design.

Voiturette Races



About this time, too, there was a growing interest in Voiturette Races. They were ordinary cars, with single or twin cylinder engines and although the racing evh-icle was often much modified, technically (as far as the public were concerned) they were production cars. The ball was set rolling when a Paris newspaper organised a highly successful voiturette race. Before long, this type of competition was taking Europe and England by storm. Most manufacturers tried to hitch their star to racing publicity and to do this successfully, they had to extract the last ounce of power from the diminutive power units. De Dion was the most successful designer of all. His light, fast revving single-cylinder design became standard reference for all designers and did much to revolutionise the design of the slow revving, rather ponderous engines of the day.

From that pont on car engines grew smaller, lighter and more powerful. Designers learned how to dispense with frictional and drag losses which once crippled the best of engines. Improved aerodynamic design, the reduction in weight of reciprocating parts, the elimination of heavy flywheels or cumbersome gearboxes and the improved efficiency of ball bearings all played an important part in diminishing the dimensions. But the biggest advance of all was in the design of the engine itself. Starting from the top down was the cylinder head design itself. Initially the side valve engine held supreme (though Fiat and other manufacturers successfully demonstrated overhead-valve designs at the turn of the century). Ingenious variations on valve design were produced but no one permanently displaced the poppet valve.

Sir Harry Ricardo



By 1908 inclined overhead valves were fitted to Grand Prix designs but few fully understood their significance until a brilliant young man named H. R. Ricardo (later Sir Harry) appeared on the British motoring scene. He soon proved himself one of the most brilliant car designers of all time and was responsible for the record breaking 3-litre twin overhead camshaft Vauxhall. Ricardo eventually formed a firm of consulting engineers, specialising in engine design and high speed cylinder heads. He (and other designers) devised intricate experiments la demonstrate the effect of turbulence within a combustion chamber. And it was Harry Ricardo who demonstrated for the first time the importance of combustion chamber design, the positioning of the spark plug and the design of the piston top.

The story goes that when called in to vet the design of a prototype built by a famous manufacturer, Ricardo extracted twice the intended horsepoper, merely by redesigning the cylinder head and manifolding. The importance of air flow was another problem tackled by Ricardo. After he had shown that a hemispherical cylinder head (made possible by an overhead-valve design) gave maximum turbulence, he proceeded to find means of improving the flow of gases into and out of the combustion chamber. This eventually developed into a study of its own and later in Europe and America there were firms devoted entirely to the study of gas flow. Engine designers would call in a consultant who would modify any design in accordance with the theories laid down by Ricardo and his successors.

Volumetric Efficiency



Unless the position and shape of ports gave free flow to and from the cylinder, it would not be possible to develop full power, nor would maximum b.h.p. be developed at higher r.p.m. The shape, size, lift and angles of the valves as well as the shape of the piston crown and the position of the spark plug all play major roles in e ngine efficiency. Optimum power can only be obtained when all of these factors are right. Through the years, the old rule of thumb methods eventually gave way to scientific studies. By the 1950s there were special machines used to determine precisely the rate at which gas was flowing through an engine.

The ratio of the flow to the actual volume swept by the pistons was the volumetric efficiency. In the earliest days, this was somewhere around 20%. A really efficient high speed engine by the 1950s gave somthing approaching 90%. Thus, the discoveries relating to volumetric efficiences were another very signicant reason for the diminishing dimension. Arguably the next more important innovation in the quest for better speed was the nature of fuel and resultant increase to the compression ratios that became standard practice on racing engines. At one time a compression ratio of 4 to 1 was considered the limit. Anything above that resulted in detonation and - if taken to the extreme - mechanical failure. The first discoveries of antiknock characteristics were most important. When most of the charge has been burnt, towards the end of combustion, the pressure and temperature of the unburnt gases reaches a critical point and the gas explodes, burning instantly. The waves of pressure resulting from this detonation strike the cylinder walls, giving rise to the sound known as "pinging".

Volumetric Efficiency



Experimentation during the 1930s showed that the nature of the fuel used and the comoression ratio were the two most important factors in eliminating detonation. As certain "anti-knock" additivities were discovered, it was possible to raise the compression ratio. The actual limit to the power which can be extracted from an engine is governed by the highest compression ratio that can be used without detonation occurring. Engine designers have found through the years that to achieve maximum compression, the following setting are important: the distance travelled by the flame front; the relative positions of the plug and exhaust valves; the direction in which combustion spreads; the amount of turbulence. Successive designs gave rise to a better understanding of the factors, so the b.h.p. of an engine of given volume would rise.

Even before designers had fully digested the implications of volumetric efficiency and detonation limits, a third factor came prominently into the picture. It was piston speed. The ratio between piston speed and engine power was, at one time, a hot bed of controversy. As soon as designers found that light, fast revving engines, could apparently click a scornful tailshaft at the long stroke, slow revving units, there was a mistaken belief that the faster an engine could be made to rev, the greater would be its power output. By 1913 some of the hot European machinery was reaching piston speeds of 3,000 ft. per minute. But subsequent experiments demonstrated that piston speed alone was not a controlling factor in b.h.p.

Dr. Lanchester



As a case in point, the successful Mercedes racing engines of 1924 developed 60 b.h.p. per litre, with piston speeds of 3820 ft./min. Yet the engine fitted to the 300 SL in 1955 developed 115 b.h.p. per litre at 3850 ft./min. This demonstrated that the output of Mercedes engines was virtually double without resort to even a perceptible increase in piston speeds. Automotive engineers gradually started favouring a theory originally propounded in 1905 by the great Dr. Lanchester. A summary of his rather involved and intricate data is that the output of the engine is proportional to the piston speeds divided by the square root of the stroke/bore ratio. A British engineer, Mr. F. R. King, set out in 1957 to prove how close this theory had been proved right by successful racing car designs through the years. The theory also showed why engineers favoured the trend to "square engines", or even "over square engines".

An engine is said to be square when its bore and stroke dimensions are equal. It is "over-square" when the bore exceeds the stroke. A good example of an over-square engine is the 300 SL Mercedes, in which the bore is 76 mm. and the stroke 68.8 mm. With a modern, unsupercharged engine a power output of 120 b.h.p. per litre was possible. In the early days when the racing giants of Europe had massive engine capacities, the accepted power out per litre was 3.5 b.h.p. The Mark III Aston-Martin 3-litre engine is generally held by classic car enthusiasts to be an outstanding example of high performance design. It developed 67 b.h.p. per litre - but it was only ten years before the Aston hit the road that an engine was first designed with an output of less than half this figure.

Laurence Pomeroy, a noted British technical journalist, stated that the Aston-Martin design was not dissimilar to that of the 1920 G.P. Ballot engine. This unit gave roughly 35 b.h.p. per litre. By the early 1960s sports car engines had surpassed the G.P. design of 40 years past. And remember too that, in these earlier times, that boost in engine design was achieved without fuel injection, supercharging, bi-fuel injection or gaseous injection system.
Lenoir designed engine of 1860
Over the flying kilometre, this 750cc Austin Seven clocked 102.28 miles per hour in 1931.

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