Williams insist there is "more to come" in terms of upgrades to its current package as it aim to close the gap to Ferrari.
The Grove-based squad finished the 2014 season as the second-fastest team behind Mercedes and they were expected to once again be the main challengers this campaign.
However, they have been overtaken by Ferrari during the first four races of this season, but performance chief Rob Smedley says they are still aiming to catch up with their Italian rivals.
"We've had four races now and it's quite clear what the order is," he is quoted as saying by F1i.com.
""We have some upgrades coming for Barcelona, but it will be a fair old challenge to catch [Ferrari] back up – especially in terms of race pace by Barcelona – but the target is that we'll catch them back up."
There is a three-week break before the next race in Spain and, like most teams, Williams will be working hard to improve their package at a "higher and faster" rate.
"I think that we're optimising fairly well the package that we've got now," he said. "There's more to come, but there's not huge chunks to come out of what we've got, but we need to develop the whole car package faster, at a higher rate and faster if we're going to catch the people in front.
"Our aim is primarily to catch the people in front. We also have to bear in mind that you've got a huge organisation, very technically able in Red Bull behind us, who will eventually get their act together and will be a lot stronger than they are now.
So we need to be looking forward but keeping an eye on what's going on behind as well. We're dealing with massive teams, very well organised teams with Ferrari in front and Red Bull behind, that's the playing field that we're in."