Le Mans 24 hours organisers the ACO have continued to support the use of diesel fuel by making very few changes to the 2007 regulations.
Audi dominated this year's race in their first year with a diesel engine, and despite performance penalties in the American Le Mans Series, the Audi R10 is currently undefeated in the series with one round remaining.
Several rival teams complained that the Audis were allowed the same size fuel tank as the rest of the field, despite diesel offering better mileage. The German cars were able to run longer than the other front-runners, and still set a blistering pace.
Next year, Peugeot will also race with a diesel engine, and the ACO will reduce the size of the fuel tanks by 10 per cent for diesel-powered cars, without restricting their performance in any other way.
ACO president Jean-Claude Plassart said: "Our regulations are framed in such a way as to encourage manufacturers to take up new challenges.
"We are delighted with the recent initiative of two major manufacturers, which have accepted the challenge to race at Le Mans with a clean diesel engine."
Since the 24-hour classic in June, the ACO has been working closely with manufacturers, fuel companies and independent engineers to review its regulations.
Plassart continued: "We came to the conclusion that corrections had to be made but with considerable caution, all the more so as those in the running for victory were separated by small gaps."
According to the ACO, the reduction of fuel tank size by 10 per cent corresponds to the difference in the amount of energy in a litre of diesel and a litre of petrol.
Restrictions will also be put in place to increase the gap between LMP1 and LMP2 cars. Lola and Porsche have raised the bar in the LMP2 class this year, often outpacing cars from the top class in the ALMS.
GT1 cars will have their air restrictors reduced by five per cent to reduce their top speeds and increase the gap to the prototype cars. GT2 cars will have the same change to keep the gap the same between the two GT classes.
LM P1: Concerning the adjustments to be made to performances between petrol and diesel-engined cars, the advantages and disadvantages linked to the use of different types of engines must be taken into account. After making this clear the A.C.O considers that for 2007 in the light of the results achieved this
year the size of the air restrictors, the supercharger pressures and the weight of all the LM P1s should remain identical to those of the 2006 season. The gap between the quantity of energy in a litre of diesel and a litre petrol being 10% the capacity of the diesel-engined cars' fuel tanks will be reduced by this amount to 81 litres.
LM P2: The performances of some of the LM P2 cars are very close to and indeed sometimes even better than the LM P1s on certain circuits so a reduction is necessary. The air restrictors will be 5% smaller. In addition, a gap of 1.5% between the best LM P1 and LM P2 laps times must be respected. If the gap is under this figure the A.C.O will take steps to re-establish it at the end of the year.
LM GT1: Given that the performance and top speed of these cars are constantly increasing approaching those of the LM P2s, their air restrictors will be reduced by 5%. As the capacity of the fuel tanks has to be adjusted according to the type of energy used (petrol or ethanol; see 'fuels' below), the amount of fuel on board the car must not exceed 90 litres.
FUEL: In 2007, the ACO will supply only one kind of petrol and one kind of diesel for the Le Mans 24 Hours and the Le Mans Series events. To meet the requests of several entrants who want to use bio fuels, the ACO is currently evaluating the possibility of supplying a type of diesel and petrol in 2008 that contain a certain quantity of bio fuel. These fuels will be compatible with current engines. However, the ACO agrees that the American Le Mans Series supply a third kind of fuel based on ethanol for its events in 2007. The capacity of the fuel tanks will be adjusted in such a way that the quantity of energy will be the same whether it is petrol or diesel. For safety reasons the capacity of the fuel tank cannot exceed 110 litres.
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