Pat Symonds has challenged Williams to improve on their third-place finish in the 2014 constructors' championship.
The Oxfordshire-based outfit showed dramatic improvement from being one of Formula 1's back-markers in 2013 to competing for podium finishes during last season.
Symonds, who is Williams's chief technical officer, has admitted that catching Mercedes and Red Bull will be a tough task, but is adamant that the team must push themselves.
Speaking at the Autosport Show, Symonds said: "We've set the bar high, we're not a team in financial troubles, we're not a team with the budgets available that our rivals have.
"It is one of the things that gives me great pleasure in beating Ferrari last year, it is not the fact that I am a competitive person, but that we beat them on half their budget! Moving on from third upwards is more difficult than going from ninth to third.
"It's a relative thing, your competitiveness, [but] we've got the best power unit [and] stability, [while] some of our rivals have new power units or new people in place, so we have to exploit our advantage of continuity that we've got, so no lower than third [is the aim]."
The 2015 season begins in Australia on March 15.
