World championship leader Fernando Alonso said the Enstone-based Renault F1 team would have to continue working hard to keep ahead of the challenging teams.

Speaking in the run-up to the San Marino GP, at Imola, on Sunday, he said Ferrari, McLaren and Honda were all good enough to win races.

He said: "Ferrari and McLaren will be our main opponents. Ferrari dropped down in the last two races, but I think they will be back. Their tyres work well at this circuit, and it is their home Grand Prix, so I expect them to be extremely competitive.

"We are in a strong situation, and we know that the team that develops most, with a strong finish to the year, will probably be champions. The drivers have a role too, because we need to tell the engineers where the car has to improve, which is what we are doing at the moment.

"It is always important to score a lot of points at the start of the year. We know Renault is the team to beat at the moment. I am really happy with our position, and very confident for the coming races."

The Spaniard won the Imola race in 2005 and aims to repeat the victory. He said: "For me, it was a win like the others a special achievement. But when you are fighting with Michael Schumacher, then I think the media talk about it in a special way, and make it something bigger.

"I enjoyed the final laps of the race last year, and it was an important race to win. But if I can do it again this year, on my own, a long way in front, then that's even better!

"The circuit is very difficult for the drivers, with the chicanes and the kerbs, and the car bumping over them. That makes it hard for us to take the same line twice in any corner, and every lap you have to feel things a little bit differently. It is tough physically, but also for the car, because there is a lot of stress over the kerbs. This is a hard race to finish."

Denis Chevrier, head of trackside engine operations, said the move from V10 to V8 engines had proved a challenge.

He said: "The V8s are still young engines, and I don't think any team was 100 per cent ready for the start of the season. At Renault, we had done a lot of mileage in the winter, encountered problems that we had worked hard to resolve, and started the season in a stronger position than some of our rivals.

"But every manufacturer is still working through the challenges encountered early in the life of a new engine, and nobody can yet say they have solved them all."

Renault will use the new R26B engine in the car being driven by Alonso's team-mate Giancarlo Fisichella in Imola. Chevrier said: "We have looked to gain performance by increasing the peak revs. In qualifying trim, we expect a gain of several tenths of a second and the final dyno tests before the Grand Prix will allow us to determine exactly how much additional performance is available during the race."