What a difference a year makes in Formula 1

In comparison to last year this edition of Formula 1 testing at Jerez was a huge success and illustrates what a difference a year makes in Formula 1.

Last year was the dawn of the new V6 turbo era, the brand new technology was hardly plug-and-play plus the cars were slower... much slower and quieter too.

Fast forward a year and lap times at the same venue are three seconds per lap faster, there is more noise and the most glaring changes are in the team line-ups, particularly Sebastian Vettel in the red of Ferrari, Fernando Alonso at McLaren and a host of rookies embarking on their first season at the pinnacle of the sport.

And looking back who was fastest of all over four days at Jerez in 2014: Kevin Magnussen in a Mercedes powered McLaren... makes you think!

At the recently concluded 2015 session in southern Spain a reinvigorated and new-look Ferrari team has emerged as an early front-runner to challenge for this year's Formula 1 championship, after posting quicker times than Mercedes in all four days of pre-season testing this week.

Kimi Raikkonen gave Ferrari another boost with the best time on Wednesday's fourth day- the quickest from anyone all week - after new teammate Sebastian Vettel was fastest over the first two days.

"These past few days of testing have produced encouraging signs. The team has worked well, both at home and at the track," said team principal Maurizio Arrivabene, who replaced Marco Mattiacci late last year in a turbulent year for Ferrari that also saw the resignation of long-standing team principal Stefano Domenicali in April.

"But above all, I am pleased that the group has rediscovered its motivation and team spirit," Arrivabene added, alluding to the rifts that tore Ferrari apart in 2014.

Raikkonen, the 2007 F1 champion, clocked a best lap of 1 minute, 20.841 seconds on the Jerez circuit in southern Spain.

However, with two further sessions left before the start of the new season, Arrivabene remains wary of forecasting success - understandably so, seeing as Ferrari failed to win a race last year for the first time since 1993.

"I don't think our competitors - one in particular [Mercedes] - have shown their true potential," he said. "I think we will only discover the truth about them and about ourselves at the last Barcelona test session."

Marcus Ericsson was second quickest Wednesday, just over one second behind for Sauber, and defending F1 champion Lewis Hamilton third fastest for Mercedes. They all completed more than 100 laps: Hamilton topping with 117.

"It's been one of our highest weeks (in terms) of mileage," Hamilton said. "The things we have to work on can be easily rectified."

Two more testing sessions- in two and in three weeks' time - should be to Raikkonen's liking, given that he holds the lap record on Barcelona's Catalunya circuit.

But Mercedes still looks the car to beat when the season opens on March 15 in Australia, since Ferrari's pace is still hard to qualify given that it could be running on a lower fuel load.

"They look like they are doing shorter runs, so more kind of qualifying attacking runs, which we are not," said Hamilton, hinting that Mercedes still has speed to spare.

"I would imagine we'll have more parts there (in Barcelona), more mechanical test items," the 30-year-old Hamilton said.

Nico Rosberg's two sessions on Sunday and Tuesday produced 308 laps of largely smooth and faultless driving, whereas Hamilton's were slightly more difficult.

Hamilton stopped just short of 100 laps on Monday, losing time because of a water leak, and on Wednesday span the car.

"Nothing much really, it was just a bit damp," Hamilton said, playing down the mishap. "I was the first on slicks."

The problems continue for both McLaren and Red Bull, which has the inexperienced 20-year-old Russian Daniil Kvyat driving instead of Vettel.

Kvyat broke the front wing on Monday and missed most of Wednesday's morning session after returning to the garage early.

Despite boasting two-time champion Fernando Alonso and 2009 F1 champ Jenson Button, McLaren is still scrambling.

A troublesome power unit, meanwhile, limited McLaren to only 12 laps over the first two days and 32 on Tuesday - the lowest of any team on day 3 of testing.

There was an improvement on the final day, with Button managing 35 laps and times substantially closer to the pack, which was perhaps the first glimmer of hope for the Woking outfit.