Dynamometer

Dynamometer (pronounced dahy-nuh-mom-i-ter)

(1) A device for measuring mechanical force or muscular power (ergometer).

(2) A device for measuring mechanical power, especially one that measures the output or driving torque of a rotating machine.

1800–1810: A compound word, the construct being dynamo + meter.  Dynamo was ultimately from the Ancient Greek δύναμις (dúnamis; dynamis) (power) and meter has always been an expression of measure in some form and in English was borrowed from the French mètre, from the Ancient Greek μέτρον (métron) (measure).  What meter (also metre) originally measured was the structure of poetry (poetic measure) which in the Old English was meter (measure of versification) from the Latin metrum, from the Ancient Greek metron (meter, a verse; that by which anything is measured; measure, length, size, limit, proportion) ultimately from the primitive Indo-European root me- (measure).  Although the evidence is sketchy, it appears to have been re-borrowed in the early fourteenth century (after a three hundred-year lapse in recorded use) from the Old French mètre, with the specific sense of "metrical scheme in verse”, again from the Latin metrum.  Metre (and metre) was later adopted as the baseline unit of the metric system.  Dynamometer is a noun; the noun plural is dynamometers.

The modern meaning of dynamometer (measuring the power of engines) dates from 1882 and is short for dynamo-machine, from the German dynamoelektrischemaschine (dynamo-electric machine), coined in 1867 by its inventor, the German electrical engineer Werner Siemans (1816-1892). Dynamometers, almost universally referred to as dynos, are machines which simultaneously measure the torque and rotational speed (RPM) of an engine or other rotating prime-mover so specific power outs may be calculated.  On modern dynamometers, measures are displayed either as kilowatts (kW) or brake-horsepower (bhp).

Evolution of the Turbo-Panzer

Porsche 917 Flat 12 being run on factory dynamometer, Stuttgart, 1969.

During the last hundred years odd, the rules of motor sport have been written by an alphabet soup of regulatory bodies including the AIACR, the CSI, the FISA and the FIA and these bureaucrats have made many bad decisions, tending often to make things worse but every now and then, as an unintended consequence of their dopiness, something really good emerges.  The large displacement cars of the mid-1960s contested sports car racing in one of the classic eras in motorsport.  Everyone enjoyed the competition except the rule-making body (the CSI, the Commission Sportive Internationale) which, on flimsy pretexts which at the time fooled nobody, changed the rules for the International Championship of Makes for the racing seasons 1968-1971, restricting the production cars (of which 50 identical units had to have been made) to 5.0 litre (305 cubic inch) engines with a 3.0 litre limit (183 cubic inch) for prototypes (which could be one-offs).  Bizarrely, the CSI even claimed this good idea would be attractive for manufacturers already building three litre engine for Formula One because they would be able to sell them (with a few adaptations), for use in endurance racing.  There’s no evidence the CSI ever asked the engine producers whether their highly-strung, bespoke Formula One power-plants, designed for 200 mile sprints, could be modified for endurance racing lasting sometimes 24 hours.  Soon aware there were unlikely to be many entries to support their latest bright idea, the CSI relented somewhat and allowed the participation of 5.0 litre sports cars as long as the homologation threshold of 50 units had been reached.  A production run of 50 made sense in the parallel universe of the CSI but made no economic sense to the manufacturers and, by 1968, entries were sparse and interest waning so the CSI grudgingly again relented, announcing the homologation number for the 5.0 litre cars would be reduced to 25.

The famous photograph of the 25 917s assembled for the CSI’s inspection outside the Porsche factory, Stuttgart, 1969.

This attracted Porsche, a long-time contestant in small-displacement racing which, funded by profits from their increasingly successful road-cars, sought to contest for outright victories in major events rather than just class trophies.  Porsche believed they had the basis for a five litre car in their three litre 908 which, although still in the early stages of development, had shown promise.  In a remarkable ten months, the parts for twenty-five cars were produced, three of which were assembled and presented to the CSI’s homologation inspectors.  Pettifogging though they were, the inspectors had a point when refusing certification, having before been tricked into believing Ferrari’s assurance of intent actually to build cars which never appeared.  They demanded to see twenty-five assembled, functional vehicles and Porsche did exactly that, in April 1969 parking the twenty-five in the factory forecourt, even offering the inspectors the chance to drive however many they wish.  The offer was declined and, honour apparently satisfied on both sides, the CSI granted homologation.  Thus, almost accidently, began the career of the Porsche 917, a machine which would come to dominate whatever series it contested and set records which would stand for decades, it’s retirement induced not by un-competitiveness but, predictably, by rule changes which rendered it illegal.  

917LH (Langheck (long tail)), Le Mans, 1969.

The ten month gestation was impressive but there were teething problems.  The fundamentals, the 908-based space-frame and the 4.5 (275 cubic inch) litre air-cooled flat-12 engine, essentially, two of Porsche’s 2.25 (137 cubic inch) litre flat-sixes joined together, were robust and reliable from the start but, the sudden jump in horsepower meant much higher speeds and it took some time to tame the problems of the car’s behaviour at high-speed.  Aerodynamics was then still an inexact science and the maximum speed the 917 was able to attain on Porsche’s test track was around 180 mph (290 km/h) but when unleashed on the circuits with long straights where over 210 mph (338 km/h) was possible the early cars could be lethally unstable.  The first breakthrough in aerodynamic dynamic was serendipitous.  After one high speed run during which the driver had noted (with alarm) the tendency of the rear end of the car to “wander from side to side”, it was noticed that while the front and central sections of the bodywork were plastered with squashed bugs, the fibreglass of the rear sections was a pristine white, the obvious conclusion drawn that while the airflow was inducing the desired degree of down-force on the front wheels, it was passing over the rear of body, thus the lift which induced the wandering.  Some improvisation with pieces of aluminium and much duct tape to create an ad-hoc, shorter, upswept tail transformed the behaviour and was the basis for what emerged from more extensive wind-tunnel testing by the factory as the 917K for Kurzheck (short-tail).

Porsche 917Ks, the original (rear) and the updated version with twin tail-fins, Le Mans, 1971.

The 917K proved a great success but the work in the wind tunnel continued, in 1971 producing a variant with a less upswept tail and vertical fins which bore some resemblance to those used by General Motors and Chrysler a decade earlier.  Then, the critics had derided the fins as “typical American excess” and “pointlessly decorative” but perhaps Detroit was onto something because Porsche found the 917’s fins optimized things by “cleaning” the air-flow over the tail section, the reduction in “buffeting” meaning the severity of the angles on the deck could be lessened, reducing the drag while maintaining down-force, allowing most of the top-speed earlier sacrificed in the quest for stability to be regained.

The Can-Am: A red Porsche 917/10 ahead of an orange McLaren M8F Chevrolet, Laguna Seca, 17 October 1971.  Two years to the day after this shot was taken, the first oil shock hit, dooming the series.

The engine however had been more-or-less right from day one and enlarged first to 4.9 litres (300 cubic inch) before eventually reaching the 5.0 limit at which point power was rated at 632 bhp, a useful increase from the original 520.  Thus configured, the 917 dominated sports car racing until banned by regulators.  However, the factory had an alternative development path to pursue, one mercifully almost untouched by the pettifoggers and that was the Canadian-American Challenge Cup (the Can-Am), run on North American circuits under Group 7 rules for unlimited displacement sports cars.  Actually, Group 7 rules consisted of little more than demanding four wheels, enveloping bodywork and two seats, the last of these rules interpreted liberally.  Not for nothing did the Can-Am come to be known as the “horsepower challenge cup” and had for years been dominated by the McLarens, running big-block Chevrolet V8s of increasing displacement and decreasing mass as aluminium replaced cast iron for the heaviest components.

The abortive Porsche flat-16.

In 1969, the Porsche factory dynamometer could handle an output of around 750 bhp, then thought ample but even 635 bhp wouldn’t be enough to take on the big V8s but, for technical reasons, it wasn’t possible to further to enlarge the flat-12, Porsche built a flat-16 which pushed their dynamometer beyond its limit, the new engine rated at 750 bhp because the factory didn’t have the means to measure output beyond that point.  Such a thing had happened before, resulting in an anomaly which wasn’t explained for some years.  In 1959 Daimler released their outstanding 4.5 litre (278 cubic inch) V8 but their dynamometer was more antiquated still, a pre-war device unable to produce a reading beyond 220 so that was the rating used, causing much surprise to those testing the only car in which it was ever installed, the rather dowdy Majestic Major (1959-1968).  The Majestic Major was quite hefty and reckoned to enjoy the aerodynamic properties of a small cottage yet it delivered performance which 220 bhp should not have been able to provide, something confirmed when one was fitted to a Jaguar Mark X.  Unfortunately, Jaguar choose not to use the Daimler V8 in the Mark X, instead enlarging the XK-six, dooming the car in the US market where a V8 version would likely have proved a great success.

The Can-Am: Porsche 917/10, Riverside, 1972.

Estimates at the time suggested the Porsche flat 16 delivered something like 785 bhp which in the Can-Am would have been competitive but the bulk of the rendered it unsuitable, the longer wheelbase necessitated for installation in a modified 917 chassis having such an adverse effect on the balance of the car Porsche instead resorted to forced aspiration, the turbocharged 917s becoming known as the turbopanzers.  Porsche bought a new dynamometer which revealed they generated around 1100 bhp in racing trim and 1580 when tuned for a qualifying sprint.  Thus, even when detuned for racing, the Can-Am 917s typically took to the tracks generating more horsepower than the Spitfires, Hurricanes and Messerschmitt which fought the Battle of Britain in 1940.  Unsurprisingly, the 917 won the Cam-Am title in 1972 and 1973, the reward for which was the same as that earlier delivered in Europe: a rule change effectively banning the thing.

The widow-maker: 1975 Porsche 930 with the surprisingly desirable (for some) “sunroof delete” option.

The experience gained in developing turbocharging was however put to good use, the 911 Turbo (930 the internal designation) introduced in 1975 originally as a homologation exercise (al la the earlier 911 RS Carrera) but so popular did it prove it was added to the list as a regular production model and one has been a permanent part of the catalogue almost continuously since.  The additional power and its sometimes sudden arrival meant the times early versions were famously twitchy at the limit (and such was the power those limits were easily found), gaining the machine the nickname “widow-maker”.  There was plenty of advice available for drivers, the most useful probably the instruction not to use the same technique when cornering as one might in a front-engined car and a caution that even if one had had a Volkswagen Beetle while a student, that experience might not be enough to prepare one for a Porsche Turbo.  Small things apparently could make a difference, one source suggesting those wishing to explore a 930’s limits should try to get one with the rare “sunroof delete” option, the lack of the additional weight up there slightly improving the centre of gravity to the extent one could be travelling a little faster before the tail-heavy beast misbehaved.  It may be an urban myth but is vaguely plausible although, at best it would seem only to delay the inevitable.

In what may have been a consequence of the instability induced by a higher centre of gravity, in 2012 Lindsay Lohan crashed a sunroof equipped Porsche 911 Carrera S on the Pacific Coast Highway in Santa Monica, Los Angeles.  Clearly, Ms Lohan should avoid driving Porsches with sunroofs.