Lance Stroll says Williams' car problems equate to up to a 30 horse power deficit.
The British team is stuck in arguably its worst ever crisis, with the slowest car in Formula 1 and boss Paddy Lowe admitting there is no light at the end of the tunnel.
"I don't expect a lot of progress at Silverstone. We are counting on the next package," he admitted.
Lowe is in charge of the technical side at Williams, but he said it is no simple thing to set up the sort of structure he put together at Mercedes.
"Not everything that worked well there can be moved here. We need time for that," he said.
Even Robert Kubica, the team's experienced test driver, is frustrated, particularly after his running on Friday in Austria.
"I did things that are not normally done and which should not be done by the driver.
We must understand what is wrong with this car so that we don't just have the same thing next February," said the Pole.
Stroll, Williams' highly funded Canadian race driver, sounds even more frustrated.
"Unfortunately we have no performance, and it's the same story at every race. We are too slow.
It's like being 25 to 30 horse power down, so you can't do anything," Stroll told La Presse.
