A few years ago the Automobile Club de l’Ouest, who organise the Le Mans 24 hour race, realized that preparation for the annual event was not something that happened a day or two before the race, but was a serious long-term programme of experimentation and testing. To assist the serious competitors a Test Weekend was inaugurated in the spring-time in order that .experimental work could be undertaken on the Sarthe circuit under full-race conditions. The people behind the organising club have always lived in a world of their own, knowing they have a unique race and being strong enough to stand out on their own against any problems. For a number of years they persisted in running their Test Weekend at the same time as the BOAC long-distance race at Brands Hatch, causing unnecessary problems to the main sports prototype contenders. As well as providing competitors in the 24 hour race with a chance to do some testing early enough to be able to return to base and re-design or modify before the June race, the Test Weekend also gave the organisation and circuit services a chance to have a practice run, and while the whole charade of Le Mans was not in hill swing during this practice, the major items Were set in motion. A surprising number of spectators began to turn up at these Test Weekends, until the numbers would have done justice to an average British race meeting. As there was not a great deal to see, unless you were behind the scenes and could watch the details of a test programme, the Automobile Club de l’Ouest had the bright idea of putting on a 3 hour race at the end of the weekend, the thought being that the teams who were there testing would then race their cars in a short version of the June event. However, this idea misfired, for few of the major teams were interested in taking part in a non-event and it was left to enthusiastic private teams to support the 3 hour race. In order to fill the grid for this race entries were taken from competitors who were not taking part in the 24 hour event in June, so this called for a special practice session for the 3 hour competitors, which naturally took away some of the testing time for the 24 hour competitors. in those who complained, it was pointed out that if they entered for the 3 hour race, they could have extra practice time, but the A.C. de l’Ouest officials seemed unable to realize that an experimental test car doing a few laps and then having alterations made, was not the vehicle to use in a 3 hour endurance race; nor could they see that teams who were out to win the 24 hour race were not likely to be. interested in a 3 hour club race.
All the time the crowds of spectators turning up for the Test Weekend were getting bigger, and feeling that something more should be offered for the entry fee being charged to the public, the organisers increased the 3 hour race to 4 hours, with more practice for those taking part in it; and less for those who were there only for test purposes. This year the A.C. de l’Ouest surpassed themselves for they organized a 2 hour race for club members, in addition to the 4 hour race, and really went overboard by making the 4 hour race a two heat affair of a hours each. Thus with 6 hours of racing due on the Sunday, with separate practice sessions for the two groups of competitors, there was not much time left for testing purposes for those interested in the 24 hour event in June, in fact, it allowed only 3.1/2 hours early on Saturday morning, 2, hours late on Saturday afternoon and 1.1/2 hours early on Sunday morning, a mere 7 hours in a so-called Test Weekend. One can only hope that the A.C. de l’Ouest come to realize that testing for the 24 hour race is getting in the way of their programme for the Test Weekend, and they will then scrub it altogether and have another weekend set aside for the 24 hour competitors, preferably without the public being admitted, so that the teams will be allowed to get on with what they want to do, without having to provide a spectacle, which is the whole point of a “test” session as distinct from a “practice” session.
The main contenders for this year’s 24 hour race are Matra-Sinica, Alfa Romeo, Gulf Research and Porsche and all four teams used the weekend of March 23/24 for development and test work. Matra ran a single 1973 car, with heavy-duty Porsche-designed gearbox and bodywork and air intake modifications, as part of a 30 hour engine test programme, using drivers Beltoise, Pescarolo, Larrousse and Jacier. The car was entered in the 4 hour race purely to get more running time, and when the starter motor packed up during a refuelling stop they ignored all the rules and push-started the car, Carrying on with their test programme regardless of the rules. Alfa-Romeo had two of their horizontally opposed 12-cylinder engined cars running, with Stornmelen and Merzario driving and between experiments with different body panels and a new Formula One type of air intake above the engine, Merzario set a fastest lap in 3 min. 31.0 sec., approx. 144.5 m.p.h. and the Autodeha team demonstrated that they intended to be in the fore-front of the 24 hour,. if not at the end. In the 4 hour race an Alfa Romeo was leading when a drive-shaft broke. Gulf Research used two of their 1973 cars re-numbered GR7/1 and GR7/2, updated in body-Shape, rear suspension and overall weight, still with Cosworth V8 engines, the former having a XE gearbox/transmission unit and engine with “softer” camshafts and lower compression ratio, and the latter being in 1,000 kilometre or “sprint” trim, with the Hewland gearbox and the Cosworth V8 in Grand Prix trim. Bell drove the lightweight car and Schuppan the “endurance” car. Not wishing to get involved in actual racing John Wyer did not enter the Gulf cars for the 4 hour comedy and consequently was restricted on running time. Another competitor who suffered from the limited time available was de Cadenet with his Cosworth V8 powered special based on a design by the Brabham man Gordon Murray, and using various Brabham suspension components.
The Porsche factory team were present, heavily disguised as the Martini Racing Team, sponsored by Martini & Rossi, and had two turbo-charged Porsche 911 Carrera RSR coupes with Muller, van Lennep, Koinigg and Schurti driving. Since the advent of exhaust driven superchargers blowing high pressure air into the inlet tracts of fuel-injected engines, horsepower figures have become academic and almost a journalistic joke. An extra 100 b.h.p. being spoken of as lightly as a to thou rebore. It all started when Porsche adapted two exhaust turbo-chargers to a 917 engine and casually claimed a good round figure of 1,000 b.h.p. In Can-Am racing the turbo-charged 917 Porsche frightened away the only two serious competitors before it got under way, the magic 1000 b.h.p. doing the trick without anyone driving. With everyone buying turbo-Porsches for Can-Am racing there was no yardstick on the claimed power output. The merry-go-round of horsepower has now restarted with the turbo-charged 6 cylinder Carrera, figures quoted varying from 450 b.h.p., through 475 b.h.p. to 500 b.h.p., but whatever they were giving neither of the works cars could get rid of the Ligier coupe, with its centrally-mounted Citroen-Maserati 3-litre V6 engine, and the neat blue coupe with full-width rear aerofoil and stabilizing fins, driven by Guy Chasseuil, was a continual embarrassment to the cars from Zuffenhausen for the whole weekend, much to the joy of the partisan crowd and the immense pleasure of Guy Ligier, the constructor.
While the Ligier kept going for the two 2-hour heats and won the 4 hour event on aggregate, one turbo-Porsche blew up its engine and the other blew up its Eberspacher turbo-charger. Doubtless, Porsche will get them sorted out in due time. The turbo-charger is mounted behind the engine, in an elongated tail, with the exhaust pipes from the two banks of cylinders of the flat six Carrera engine running into the underside of the turbo body. It exhausts on the left side with the pressure regulated waste-gate also on the left. The air turbine is on the right, fed by a large fibreglass duct taking air from a side duct in the tail of the car. The high-pressure air travels through a large diameter pipe to a tubular manifold above the engine, which splits into two manifolds, one for each bank of three cylinders, and these join on to the down-draught inlet tracts in which the injector nozzles for the fuelinjection are located. On each branch of the central manifold there is a rearward facing exhaust port containing a butterfly valve which is connected to the main throttle linkage so that when the throttles open, these butterfly valves close, and when the main throttles are closed the “blow-oft” butterfly valves open, letting the air pressure in the manifold exhaust into the engine compartment. In the centre of the fascia is a large screw knob that controls the amount of turbo-charge being applied to the engine. It is not so much for screwing on more blower pressure, as for screwing it off and has been tried in Can-Am racing, the idea being that the installation is set at 1.4 atmospheres, or whatever is decided upon on the test-bed and if the driver has a commanding lead or the opposition has disappeared, he can then wind off the blower pressure thus easing the strain on the engine. If an unexpected challenge appears he can always wind it back on again. During the testing an inter-cooler was tried between the blower and the central manifold on one car, taking the form of a very thick matrix with the high-pressure air passing through the tubes and ducted air from the top of the tail passing through the matrix. This lowering of intake charge temperature was said to be good for another 50 b.h.p. The result of all this strain put on the Carrera engine was that on one car the clutch exploded out through the bell-housing and on the other the engine broke vital internal parts. Development work always brings its problems. In order to stay within the 3 litre capacity limit for sports/prototypes the turbo-charged Carrera engines were reduced to 2,142 c.c. so that when multiplied by 1.4, the C.S.I. equivalent factor for supercharged engines, they are rated at 2,998.8 c.c.
Among the things learnt at the Test Weekend were that the Alfa Romeos and Matra are very thirsty, running about 3/4 hour on a tankful of fuel (120 litres maximum) as were the turbo-charged Porsches, so that pit stops, mechanics, team organisation and control will still play a vital part in the 24 hour race, with something like 32 pit stops envisaged for the thirstier cars.