Bianchi's MR02 found over a second on the final day of the test, ending up ahead of the Toro Rosso of Daniel Ricciardo and matching the pace of Charles Pic's Caterham.
Although the F1 rookie was cautious about reading too much into the times, he believes Marussia - which will have KERS for the first time in 2013 - has made good progress.
"If you look at the lap times, yes, we've improved a lot," said Bianchi when asked by AUTOSPORT if he thought Marussia was one of the winter's top improvers.
"It's a small surprise that we did quite a good improvement and I'm happy with that.
"Even from my side, just from Saturday to Sunday, it is a big improvement. But we don't know what people were doing so it is difficult to say what the [relative] improvement is."
Bianchi still expects the challenge of joining the midfield battle to be tough.
"We have to be realistic - it'll be difficult to beat the cars in the midfield, but we'll try our best," he added. "You never know..."
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