Rossi boosted by new exhaust.

Fresh his sixth victory of the season, Valentino Rossi and the factory Yamaha team joined rivals from Honda, Kawasaki and Proton in testing at the Estoril circuit on Monday.

For its last test ahead of the final five races - which will decide the destination of the 2004 world championship - Yamaha provided championship leader Rossi with a new exhaust system, engine parts and electronics.

In contrast to the new front fairing tested after Brno, Rossi gave a clear thumbs up to the new 'slash cut' exhaust (top two pictures) - which has exits on both sides of the bike. Rossi is expected to use the new non-silenced design at the Japanese Grand Prix on September 19. The standard M1 exhaust system is shown in the lower picture.

"We tried new pipes, a different exhaust system, it's good and I like it," stated Rossi. "From the bottom power level, the engine characteristic becomes more smooth and sweet. I like it. We tested it all day and everyone agreed it's good."

"Valentino had a beneficial day, which I think could put us in a good position for the final part of the championship," confirmed Factory Yamaha team manager Davide Brivio. "Everything is working well, we seem to have made a small step today.

"It's our last chance to test before the end of the season and with five races to go, so we wanted to improve and check as many things as possible. We have concluded our plan so we hope to be prepared for these last races," added the Italian.

Rossi - 29-points ahead of Telefonica Honda's Sete Gibernau - completed a total of 80 laps on Monday, with a best time of 1min 38.31secs, good enough to put him to put him third fastest behind the Catalan and his Texan team-mate Colin Edwards. The #46 then left Estoril for a short break before starting the long journey to Motegi.

Yamaha have been expected to provide a new, more powerful, engine for Rossi ever since Donington but - with the solid championship lead - now appear to feel it could be too big a risk from a reliability point of view. As such, the new engine will only been seen when Yamaha believe it to be 'bullet-proof'.

Meanwhile, Rossi's team-mate Carlos Checa continued working on various settings with his M1 machine, as well as tyre testing. The Spaniard, who lapped 0.59secs slower than Rossi, will continue testing today (Tuesday).