Boullier: If it was only about drag we would have fixed it

Speaking to Sky Sports after the Chinese Grand Prix weekend, Boullier conceded, "We need to understand why we are slow in qualifying, why we are better in the race and why we are behind the other Renault teams."

With Red Bull as a benchmark, McLaren began their Renault-power era believing that they would be able to go toe-to-toe with the energy drinks outfit, but it has not panned out as they dreamt.

Qualifying is their Achilles heel with their star driver Fernando Alonso's best qualifying in three races being 11th place on the grid at the season-opener. In Bahrain and China, he started from 13th.

However thanks to the Spaniard's tenacity and gutsy performances he has scored points in all three races, but comparisons to Red Bull and even Renault's own works team show that the current McLaren chassis is seriously lacking. Their preseason predictions way off the mark.

Indeed the Woking outfit were on the back foot from the moment testing began and as a result have been playing catch-up ever since. The roll-out of updates has been delayed as a consequence. Their next big update is now scheduled to break cover during the Spanish Grand Prix weekend.

With that in mind, Boullier added, "From that point, we will see performance-wise where we are."

But he also hinted that the team underestimated the task at hand, "The car has matched all the targets, so maybe that means the targets were not the right ones and we need to revise in terms of ambitions what we need to achieve."

Last year as the only team with Honda power they did not have a benchmark to compare their car with. But they insisted, even boasted, that they had the best chassis on the grid and only the engine was letting them down.

Not everyone bought their theory and this year the MCL33 has been a massive disappointment, suggesting that they were deluding themselves.

It has emerged that the aero package is not up to scratch or at least they are struggling to find an effective and efficient balance between downforce and outright speed.

Boullier admitted, "This is obviously one of the issues but it's not the only one. If it were a question of just drag in the car it would be easy to fix so we have to address - I'm going to use the word fundamentally - all aspects of the car to make sure we are where we should be."

Thus the importance of their Barcelona upgrade package is huge and the effectiveness of the bits they bolt on to their car, that weekend, will determine if they have found that elusive 'magic button' that will catapult them up the grid into Red Bull territory, their target when they ditched Honda for Renault.

For now, Alonso has been in good spirits, although far from the sharp end of proceedings he is now battling in the heart of the midpack where he has shown why he is so highly regarded.

The Spaniard has overshadowed the less experienced Stoffel Vandoorne in the first three races, the young Belgian has yet to sit in a decent F1 car produced by his team and simply does not have the experience of his veteran teammate to emulate him.

Nevertheless, in the wake of Daniel Ricciardo's victory in China, with Renault power, Alonso remains positive, "It shows us the potential of the power unit."

"It gives us confidence that with this power-unit we will be able to fight if we do a good job on the chassis side. We are not quite there and we need to close the gap and work hard and bring some updates in the next races," added the two times F1 World Champion.