Valentino Rossi has once again expressed his 'frustration' at the new MotoGP engine restrictions, which have coincided with a drop in his Yamaha's performance relative to Honda and Ducati.

A maximum of five engine changes are allowed from Brno until the end of this season (seven rounds), but it is really just a dry-run for 2010 - when only six engine changes will be allowed for the whole year.

"Unfortunately, the situation is very bad for the development of the bike because there are money problems for everybody, no tests and it is not possible to work very much on the engines because the amount of engines allowed for next year is very low," said the Italian.

"So you have to think more about the kilometres than the performance. This is quite frustrating, sincerely, for a MotoGP rider, because in past years we worked a lot more on the bikes. Now they have become more flat."

The M1s appeared a match for anything on the MotoGP grid in terms of acceleration and top speed at the start of the season, but its riders - particularly Tech 3's Colin Edwards - have felt a clear loss of corner-exit 'punch' since the rule change.

By contrast Honda seems to have gained ground on its rivals since Brno, illustrated by Jorge Lorenzo's problems in trying to pass Dani Pedrosa at Misano, while the Ducati riders state they have felt no difference since the rule came into effect.

"We have to work, because our bike is fantastic, but we don't have enough horsepower," stated Rossi. "What I mean is the setting is good in the corners, but we need some extra power because we lost a little bit from Brno."

Rossi's team-mate and title rival Lorenzo also believes Yamaha lost ground during the rule change, but thinks it may be up to the riders to try to find a solution.

"I agree with Vale. I think we lost something on the straights [from Brno]," said the young Spaniard. "Now the Ducati and mainly the Honda is faster in acceleration. But I think Yamaha is working for the new regulation for next year, so maybe the only way to improve is to improve your riding style. Which I will try to do."

Although frustrating for the riders, there is little incentive for Yamaha to reduce the factor-of-safety present in its 'long life' spec engines, since it is almost guaranteed to win the 2009 MotoGP championship with either Rossi or Lorenzo.

Honda's Pedrosa is 80 points adrift of Rossi in third, with a maximum of 100 points still to be decided.

Yamaha also holds an 85 point lead over Honda in the constructors' championship (maximum of 100 points remaining) while Fiat Yamaha has a 150 point lead over Repsol Honda in the teams' championship (maximum of 180 points remaining).