THREE of Australia's most successful motorsport racers from V8 Supercars, Formula One and MotoGP will go head-to-head in a Sydney street race when Mark Webber, Casey Stoner and Jamie Whincup fight for the title of Australian motorsport king.

The three champions have agreed to race Whincup's V8 Holden Commodore alongside Stoner's Honda CBR 1000 roadbike and Webber's Red Bull Formula One car in the ultimate showdown as the headline act of the Top Gear Festival that is coming to Sydney Motorsport Park at Eastern Creek on March 9-10.

Between them they have two MotoGP world championships, four V8 Supercars Championships, four Bathurst 1000 crowns and nine Formula One race victories.

The Top Gear Festival will this morning announce the head-to-head battle, which will also be Webber's first public appearance in his V8 Red Bull Racing machine in Sydney and Stoner's first appearance in Sydney driving his Red Bull Triple Eight Racing Commodore.

Top Gear Festival managing director Murray Hodges said the race promises to be a "once-in-a-lifetime spectacle".

"We're calling it the Australian speed showdown." Hodges said.

"To have those three guys all in their prime, the biggest names in Australian racing all here, it's a promoter's dream.

"There's a lot on the line for these guys. None of them like to lose."

The three will race around the 2.8km north circuit at Sydney Motorsport Park, which event organisers estimate will take Webber's Red Bull 50 seconds to complete a lap.

He has already promised to shatter the full 3.9km circuit's 1min 30.18sec lap record set by Craig Lowndes in 2010.Which is why Webber will start up to half a minute behind Stoner's Honda in the two-lap race. The motorbike is expected to be up to 15 seconds slower per lap.

It's likely to be the final time fans will see Stoner on a motorbike for the foreseeable future after he quit the sport at the end of the 2012 MotoGP season.

* * *

IN Melbourne yesterday, former world champion Jenson Button set the fastest time on the first day of Formula One testing a month ahead of the year's first grand prix.

Button overcame problems with his McLaren to roar back in the afternoon session with a fastest time of 1min 18.861sec over 34 laps.

Webber was second fastest after completing 73 laps in the team's new car, which Red Bull hope will deliver a fourth successive constructors' title.