Engines a la mode
Like the shape of our shoes and the cut of our clothes, engine design is subject to fashion. After years of “conventional” straight fours, V6s, V8s and V12s, the Grand Prix world is rushing to develop engines of unusual design. V10s and broad-arrow 12-cylinder power-units are now all the rage. But historian David Hebb argues that such apparently novel configurations have many precedents.
Only with the adoption of the normally aspirated 31/2-litre formula for Grand Prix and sports-car racing have manufacturers appeared to appreciate the viability of ten-cylinder competition engines, Alfa Romeo and Honda currently testing 72° V10s and Renault a 67° version for use in 1989. But more than ten years ago, in Motortechnische Zeitschift, Dipl Jug Fritz Indra of Audi wrote that the V10 seemed the optimum design for the 3-litre capacity limit then current.
Using criteria such as volumetric efficiency, mechanical losses, weight, length, centre of gravity, intake and exhaust tuning, he compared a V10 to the Cosworth V8 and to the Ferrari and Matra V12s, and concluded that a V10 (especially one of 144° included angle) had more to offer. Unbalanced secondary forces were the V10’s only obvious disadvantage; however, lndra believed these were of a tolerable order for a racing engine. In any case, the vibrations of a V10 were likely to be less destructive than those generated by a flat-crank V8 such as the Cosworth.
Historically, this out-of-balance factor has not inhibited engine designers from choosing the V10 configuration. For decades large diesels of this type have been used successfully for ship-propulsion and electrical-power generation. MAN and Burmeister & Wain, for example, manufacture huge V10 diesels (520mm bore x 550mm stroke), whose pistons are as large as a complete Grand Prix engine. Though these V10s may weigh 130 tons or more, and are capable of producing 10,550 bhp, they do not tear themselves or their mountings apart. More frequently one finds V10 engines in big lorries. MAN and Mercedes-Benz, for instance, use 18.3-litre (128mm x 142rrtm) VIP diesels (capable of developing over 460 bhp) to power some of the juggernauts they make. Part of the attraction is economic: these engines form part of a series of V6, V8, V10 and V12 motors which share components and can be machined on a common productionline.
Furthermore, for years thousands of armoured vehicles and tanks have been powered by V10 engines. One tank engine used by several armies is the 37.4-litre (165mm x 175mm) 950 bhp four-stroke diesel made by MTU. But the outstanding example in this field is the Mitsubishi 10ZG diesel which powers the new Japanese Type 88 tank. Like the MTU, this 21.5-litre V10 direct injected diesel is also turbo-supercharged and intercooled, basis is of two-stroke design and develops 1500 bhp, or an astonishing 70 bhp per litre! It might also come as a shock to the Grand Prix world to learn that Porsche has already designed, built and tested dozens of V10 engines. All this, however, was done over 45 years ago.
An air-cooled petrol motor of 11.6-litres, the Porsche V10 was one of the first of this configuration to be manufactured. It was oversquare (115mm x 110m) with alloy heads and hemispheric combustion chambers: the intake valves were 56mm in diameter and angled 45° off-centre, as were the 39mm exhaust valves.
Both valves were operated by a single camshaft placed in the V and transmitting lift to the valves through pushrods and rockerarms. The exhaust pushrods were located at an angle between the adjacent cylinders, and the intake valves opened by reverse-action rocker-arms much in the manner that had been proposed by Georges Boesch in 1924 and subsequently used by Chrysler, Peugeot, Daimler and Humber.
As well as V10s, other engines of unusual design have been proposed for the new 3.5-litre formula. Two small continental firms, Motors Guy Negre and Life, have shown or announced plans to build “W” or “broad arrow” 12-cylinder engines. Engines of this configuration consist of three banks of cylinders usually placed 45° or 60° apart. The French MGN engine reportedly weighs only 105kg (232lb) and is expected to produce over 650 bhp at 12,500 rpm. Though the MGN motor appears unusual, the “W” configuration has a long tradition. CRM, an Italian engine manufacturer of industrial engines, has for years produced high-speed W18 diesels mainly for marine use, such as those which power Azimut, the Atlantic record challenger. Because of its exceptional lightness, compactness, and fuel economy, this engine has also been recently selected to power an airship for the US Navy.
Nor is the use of W-configuration engines in aircraft new. In the inter-war period it was all the fashion with aero-engine manufacturers: Napier in England built the highly. successful Lion (two of which were adapted to power John Cobb’s Land Speed Record car); in France, Lorraine-Dietrich offered a W12 and Farman inverted “W” (M?) 18 engines; while in Italy, Isotta-Fraschini manufactured the 1500 hp W18 Asso L, a petrol forerunner of the CRM diesel.
Furthermore, this configuration has been proposed several times in the past for use in Grand Prix cars. At the end of the 1930s, Ferdinand Porsche examined the merits of an unblown W18 engine of 4.5-litres , estimating that a W18 would produce 305 bhp, or slightly more than was then available from any of the 1.5-litre supercharged engines.
About thirty years later, Ferrari took up the “broad arrow” idea. At the behest of engineer Franco Rocchi, the Maranello firm built an experimental three-cylinder “W” engine (P3C) to test components for an 18-cylinder W engine of 3-litres. When regulations limiting engines to a maximum of 12 cylinders were introduced, this design was dropped. Soon after, Rocchi left Ferrari, but he is now technical director at Life, a small Italian firm with plans to produce a W12 with 60° between the cylinder-banks.
This engine is similar to one proposed in England ten years ago by the late Harry Mundy, who schemed a 3-litre W12 which he believed would be superior to the Cosworth, Ferrari and Matra “V” cylinder designs then dominating Grand Prix racing. With an intended weight of only 325lb, Mundy’s “Trident” was light but, more significantly, it was only 20in long, about 25% shorter than the new V10s. From several criteria this configuration seems attractive: the block and crankshaft can be exceptionally short and stiff, few bearings are required and hence friction losses will be slight, firing pulses are equal and balance is superior to a V8. Additionally, since the exhaust-system consists of three four-cylinder groups, abundant knowledge about tuning is available. This latter feature may assume greater importance as designers follow the lead of motorcycle engine designers and start to configure and throttle exhaust systems to increase and broaden power-curves.
From this brief historical survey, one can see that, even in a state-of-the-art field such as Grand Prix engine design, there is very little that is truly new and that changes in design are often matters of fashion, many of which occur cyclically. However, these changes in design fashion do not come out of the blue; behind them are many factors, some of which are real and substantial, while others just reflect swings in style or even misunderstanding. For example, inlet tracts between the cams come and go almost as frequently as skirts rise and fall.
A more recent example of fashionable change is the choice of an 80° included angle for V-type engines; there is no engineering principle embodied in the choice of this angle. Honda adopted it initially just to make a 90° V6 design narrower, to fit a particular chassis. Since the Honda was successful, others have followed the fashion.
Frequently, apparent changes in fashion are really imitations of a successful design practice in other fields. The employment of “straight-eights”, a type favoured by designers in the early 1920s, owed much to aero-engine developments. Duesenburg set the fashion, having been attracted to this configuration as a result of its experience in developing and manufacturing the Bugatti U16 during the Great War. On other occasions, changes in fashion derive from engineering theory or assumptions about racing conditions. The fashion for two valves cylinder in the 1950s and early 60s drew heavily, if not always accurately, on theories about gas flow and the overriding importance of this factor in producing power.
At times, though, changes in design fashion reflect perceptions of the changing importance of other factors. In the last few years, for example, the application of aerodynamics has dominated racing-car design. Engine-power became relatively less important to the speed potential of a vehicle than the downforce which aerodynamic features could produce. Consequently, Formula One designers have preferred V6s of 80° and 90° because their compactness made it possible for air to flow more easily over wings or through ground. effect channels, thereby increasing downforce and ultimately speed.
With the introduction of turbo-supercharging, Formula One car design was altered substantially. In the past designers struggled to produce engines with enough power to exploit chassis and tyres. But suddenly with turbos, horsepower was relatively plentiful. Simply by turning up the boost and pumping more air and fuel through an engine, a designer could get power, excessive amounts of power: 1000 bhp or more.
For the first time ever, racing drivers no longer called for more power; some even whispered that there was now too much. Indeed, the experience of the Arrows-BMW cars suggests that this surfeit of turbo-power was detrimental. Running on reduced boost this year, these cars are considerably faster and more reliable than they were previously. The introduction of restrictive fuel and boost limits has brought designers back to the difficult job of trying to produce engines with the sort of power that turns a racing car into a winner. DDH (Part two next month)