The BMW Formula One engine for the 2005 season is not called P85, as one might expect, but comes with the model designation P84/5. "The name", says BMW Motorsport Director, Mario Theissen, "reflects the fact that the engine draws on the concept of the previous year's P84 unit but in a configuration that is in keeping with the modified requirements."

These requirements include a further doubling of the engine's running distance, the powerplant now has to last for 1,500 kilometres. That signifies a quadrupling of the distance covered in comparison with 2002. In 2003, for the first time, the same engine used in qualifying had to be used in the race as well. 2004 saw the introduction of the one-weekend engine rule. In 2005, engines cannot be replaced until they have covered a distance of two Grand Prix weekends.

Between Friday and Sunday, the engines have to tackle extremely diverse disciplines. During the free practice sessions, which are used for set-up work and tyre selection, the teams will now increasingly focus on sparing the engines. Theissen: "That can be achieved in two different ways: driving fewer laps or reducing engine speed. We don't want to drive less because that would cost us valuable set-up time, particularly as we want to cut down on the test drives. Curtailing the maximum engine speed is the preferred option. You don't need peak revs for set-up work and tyre selection." In future, the same set of tyres will have to be used both for qualifying and for the race.

By contrast, the first qualifying session, held as a flying lap between 13.00 and 14.00 hrs on Saturday, presents challenges of a very different kind. The time recorded in this single lap determines the starting order for the second timed lap (Sunday 10.00 to 11.00 hrs). Saturday's fastest driver is the last to go out onto the track on Sunday morning.

But a good lap time on Saturday is already half the battle towards securing a good place on the grid because from that point on, the lap times of both flying laps are added up to determine the grid order. And there is a further factor that plays an important role for final qualifying: by then the cars must have the fuel on board with which they will embark on the Grand Prix race.

As Heinz Paschen, Director of Formula One Engine Development in Munich, explains: "For the engines, the new regulations mean extreme and diverse demands. They have to last the considerable duration of two Grand Prix weekends, that's around 1,500 kilometres, and cope with qualifying sprints in between." Developing such a flexible car is an immense technical challenge.

"To cope with the radically increased demands for stability, in principle all mechanical and thermal components subjected to major loads had to be designed to be twice as robust as before. Normally that means an increase in engine size and weight, which in turn demands a sacrifice in engine speed and thus performance. In order to minimise these losses", Paschen continues, "painstaking precision work is necessary all the way down the line. That starts with the design of components, is closely linked to materials research and selection, and affects production as well as testing and quality control."

The engineers led by Heinz Paschen work in close alliance with the specialists from BMW's Research and Innovation Centre (FIZ). The 2005 engine called for a relatively rapid response as it wasn't until July 2004 that it was announced that the racing engine would have to be used over two consecutive Grand Prix weekends in 2005. "This late and incisive change to the specifications", says Paschen, "led to a major supplementary development effort. By the time this regulation was made known, the engine originally planned had already reached the testing stage."

That BMW P85 unit had to be shelved. The new project brief ran thus: on-going development based on the 2004 engine. It gave rise to the BMW P84/5. Since then, its state of design has changed by the week. Starting with the test drives in November 2004, the team has been on the road with the latest version of the BMW P84/5 at any given time. Theissen: "Our aim is to achieve endurance for the doubled service life while minimising as far as possible any sacrifice in performance. The BMW engine is to be the benchmark for Formula One in 2005 as well." The fact that the impact on the size and weight of the P84/5 has remained minimal is largely thanks to the materials specialists at the Research and Innovation Centre, who have developed new surface treatment processes for enhanced endurance.

The dress rehearsal, a long-distance run on the dynamic test rig, still takes place on the Monza circuit profile because of all the Grand Prix tracks it has the highest full-throttle percentage, although qualification for use has been raised to 1,500 kilometres.