The day after the fourth round of this year's WRC season in Portugal, which was won by the C4 WRC, Citroën Racing did some testing with the Citroën C4 WRC HYbrid4 concept car on an asphalt road close to Faro. Spanish star Dani Sordo was at the wheel.

Having been born out of the Citroën Racing team's creative desire to perfect a competitive yet innovative racer, the Citroën C4 WRC HYbrid4 project met with a warm reception when it was presented at the Paris Motor Show. The concept went on to make a hit at the Bologna Motor Show and then at the opening ceremony of the Rally Norway. Since the Geneva Motor Show, it carries the new livery of the title-winning Citroën C4 WRC.

The Citroën C4 WRC HYbrid4 was developed using Citroën's current World Rally Championship contender as a base. An electrical propulsion system has been added to the internal combustion engine, gearbox, and transmission that are specific to the WRC machine.

The addition of a 990-cell Ion Lithium battery on top of the petrol tank and a 1 25 kW electric motor driving the rear wheels puts an extra 150 kg onto the overall weight.

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This system, developed by Citroën Racing, allows the driver to choose between four different modes of functionality » explains Didier Clement, one of the race engineers.

In internal combustion mode, the Citroën C4 WRC HYbrid4 behaves exactly like one of the C4 WRCs that compete on the World Rally Championship. In internal combustion mode with energy recovery switched on, braking endurance is improved and the batteries get charged. On road sections and in the service park, electric mode with energy recovery means that there is less nuisance, increased range and less wear on the conventional engine. Finally, boost mode - which employs both the internal combustion engine and the electric motor - gives an extra 300 Nm of torque when engaged.

The two engines are linked to the same drivetrain. The driver can choose electric mode simply by switching on the ignition without starting the internal combustion engine. The gearbox paddles then give him a choice of three settings: forwards, backwards and neutral.

Didier Raso, an electrical and systems engineer, comments: The objective with this project was to be able to use the electric motor to drive on some of the road sections. This fully operational concept responds to that design brief. Citroën Racing wanted to show its ability to adapt this technology to motorsport. If at any point in the future the regulations permit the use of hybrid technology, we will be able to react straight away.

During the test session, Citroën Total World Rally Team driver Dani Sordo was able to evaluate the dynamic properties of the C4 WRC HYbrid4. One of the highlights of the day was a road section that passed through the village of Barranco do Velho, which was of course open to normal traffic. This allowed the team to assess the advantages of zero emissions in a life-sized context.

The second part of the test was a somewhat more familiar territory for Citroën Racing's development team: a narrow and twisty asphalt road, not at all dissimilar to many of the demanding stages seen on the World Rally Championship.

Following the three challenging days of Rally Portugal, which resulted in a third place for Dani Sordo, the young Spaniard looked forward to his latest task with enthusiasm. In electric mode, you can drive through villages without making the slightest noise, which is very unusual for a competition car he reported during the hybrid car's test. It's better for the environment and also more comfortable for the crew, making road sections more pleasant.

Sordo's comments on the car's pure performance were equally complimentary. On the stages, I would say that the overall behaviour of the car is slightly different to that of the C4 WRC, with more weight to the rear he reported after his first few flying kilometres in internal combustion mode. The boost function means that we can choose when to benefit from extra torque under acceleration. When it comes in, the effect is impressive.

Just as is the case on the C4 WRC, the car set-up and tyre choice allow the driver to fine-tune the handling. The feeling is on the whole the same as the one I have with the standard rally car, added Sordo. And I love the way that the C4 goes on asphalt!

Throughout this test session, which well and truly underlined the creativity of Citroën Racing, the Citroën C4 WRC HYbrid4 demonstrated all the credentials that make it an important technological advance in rallying. Driving a C4 HYbrid4 that nonetheless has several things in common with his usual car, Dani Sordo successfully completed a fruitful test in which several valuable lessons were learned for the future.