* Vettel aims for fourth title in a row
* Final year of V8 engines
* Hamilton with Mercedes, Perez at McLaren
By Alan Baldwin
LONDON, March 8 (Reuters) - No driver in the history of Formula One has won four championships before the age of 30 but being first has become something of a habit for Sebastian Vettel.
The 25-year-old Red Bull driver became the youngest triple champion last year and the German with the cheeky grin and raised single finger will start the new season in Australia next week as favourite for a fourth title.
The youngest points scorer, podium finisher, race winner and champion - who could become only the third driver after Juan Manuel Fangio and Michael Schumacher to win four successive crowns - may be facing his toughest task yet, however.
Vettel ended testing in Spain last weekend without fanfare and as the only driver from the leading five teams to fail to top any of the end-of-day timesheets over the 12 days.
"I would say that we never had a winter that was less conclusive than this one," Vettel told reporters in Spain, recognising that the team had not ticked all their boxes on the test track.
"I think it is impossible for all of us to read the pace of the cars and to make out any favourites."
While rivals suspect that Red Bull have deliberately masked the potential of Adrian Newey's latest creation, there is hope that the gap between the champions and the rest may have narrowed.
Vettel, who took his first crown by stealth in 2010 and his third last year with a second-half surge, will still be the man every driver wants to beat when the red start lights go out.
The lifelong Beatles fan may have a long and winding road ahead of him but even if it all starts off as a bit of a mystery tour, magical or otherwise, he has every chance of staying at number one with his own fab four.
"He is still the favourite," said Frenchman Alain Prost, the only other four-times Formula One champion, who took his last title in 1993 at the age of 38. "Behind him, it's hard to say."
The swansong for the screaming V8 engines, before they are swept away in 2014 by the arrival of a costly new V6 turbocharged unit with energy recovery systems, means the regulations are barely changed this season.
New Pirelli tyre compounds, designed to encourage more frequent pitstops and overtaking with high levels of degradation, introduce an element of uncertainty however.
"I'm not sure there will be a surprise package among the teams," Red Bull team boss Christian Horner told Reuters this week. "The surprise package this year could be the tyres."
Last season started with seven different winners in the opening seven races and this year saw nine different drivers leading the timesheets on the first nine days of testing.
"We're not on our own, that's for sure," said Vettel's Australian team mate Mark Webber of the level of competition the champions face.
After three double championships in a row, Red Bull may have less pressure on them than rivals starved of success but the battle could be faster and more furious than ever.
Fernando Alonso, the double world champion who was overall runner-up last year, declared his new Ferrari F138 to be 200 times better and on another planet compared to the old F2012 at the same point last year.
"Last year was the best year of my career and I was very happy with the performance, but I think this year will be better," said the Spaniard, voted driver of the year by team principals last season despite Vettel's success.
"We have a better starting point, and I have learned from some mistakes of last year...I have prepared better. I am better than last year," added Alonso of a season that coincides with the 25th anniversary of team founder Enzo Ferrari's death.
Mercedes put in some impressively quick laps, after a shaky start, with both Lewis Hamilton and Nico Rosberg well inside the Barcelona race lap record while also putting in the hard miles.
How 2008 champion Hamilton goes after a move that surprised many is one of the big questions to be answered and he has sounded more confident after initially playing down his prospects.
"We will definitely be able to win a race at some point," said the Briton, who plans to take his Bulldog 'Roscoe' to some races after securing a special pass from Formula One supremo Bernie Ecclestone.
McLaren's Jenson Button is now Formula One's most experienced driver, following the retirement of Michael Schumacher, and has young Mexican Sergio Perez as his team mate in place of Hamilton.
A championship for McLaren, on the 50th anniversary of the company's founding by the late New Zealander Bruce McLaren, would be special. Perez has said he wants it to be his.
Button is one of five world champions on the starting grid, which has been reduced to 11 teams and 22 cars following the demise of Spanish strugglers HRT who failed to score a point in three seasons.
There are no new races, with the calendar shrinking to 19 grands prix from a record 20 after New Jersey's planned arrival had to be postponed to 2014, but plenty of new faces.
Sauber, Caterham and Marussia have all-new line-ups with a fistful of rookies set to make their debuts in Melbourne.
Britain's Max Chilton and Frenchman Jules Bianchi are newcomers at Marussia, while Caterham have Frenchman Charles Pic joining from their tail-end rivals and Dutchman Giedo Van der Garde arriving.
Swiss-based Sauber have Germany's Nico Hulkenberg, moving from Force India to join Mexican rookie Esteban Gutierrez, while Adrian Sutil returns to Force India after a year on the sidelines following his conviction for grievous bodily harm.
Finland's Valtteri Bottas will be making his race debut at Williams with Mika Hakkinen as mentor and manager.
Headlines are sure to be made off the track as well, with the possibility of a postponed flotation of Formula One resurfacing while Ecclestone and the governing FIA continue efforts to sign a new commercial 'Concorde agreement' after the last one expired.
Formula One faces a busy, and noisy, year ahead. (Editing by Clare Fallon)