Toro Rosso will use the same car as Red Bull, but fitted with a Ferrari engine rather than the Renault used by their parent team.
Vettel, who finished third in the first race of the season, admitted improvements are needed for the Red Bull car ahead of qualifying on Saturday.
Three times this season, a Red Bull car has been undone by a faulty alternator, including last weekend when it forced Mark Webber out of the race.
The high-speed track suits the Red Bull car and there remain questions about the Brawn car's ability to be competitive in the lower ambient temperatures that are usual at Spa-Francorchamps.
Vettel took the first victory for a Red Bull-designed car last year when he won the Italian Grand Prix while driving for junior team Toro Rosso.
Red Bull had a quick car all year and Sebastian has certainly done a great job of closing the season off.
Red Bull launch their new car in Jerez in Spain on Monday, ahead of a major three-day test involving many of the leading F1 teams.
Coulthard, speaking at the launch of Red Bull's new car in Spain, warned that even if the team are bought out, Button could still experience a hugely frustrating season at the back of the grid.
The Red Bull is the only car to incorporate a pull-rod rear suspension, which is incorporated into their gearbox design and means there is little room at the back of the car to add a split-level diffuser.
Red Bull has linked up with Japanese car maker Infiniti and will receive effectively free engines for the first time.
The Governor and I were talking in the car about some companies coming back -- Red Bull, right, coming back.
Red Bull driver Sebastian Vettel took his F1 car for a spin through his mountainous hometown of Heppenheim in Germany on Sunday.
In Melbourne on Sunday, the safety car came out after a late collision between Red Bull's Sebastian Vettel and Robert Kubica in his BMW Sauber.
Stoner will drive for Red Bull Racing Australia in 2013, competing in a car which won the 2010 edition of the famous Bathurst motor race.
Alonso lost out on pole to Sebastian Vettel at Hockenheim by a scant two-thousandths of a second and the car was, if anything, slightly faster than the Red Bull in the race.
Alonso's retirement handed fifth place to Mark Webber, whose Red Bull team have also made a step forward with their car.
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One insider at a top team told BBC Sport that while it was hard to be definitive about comparative pace because of the differences to lap times created by fuel loads and tyres, Ferrari appeared to have a slight advantage over Red Bull at the moment as the team with the fastest car.
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Red Bull are also expected to have some new parts on their car on Saturday.
Red Bull has previously sponsored events where records for the longest rally car jump, highest BMX jump and longest snowmobile jump were all broken.
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"Today we had a good car, and I don't think we were too far from the Red Bull pace, especially in the race, " the Spaniard said.
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Vettel's second fastest lap was in sharp contrast to Red Bull team-mate Mark Webber's performance, with the Australian's car suffering suspected engine failure.
Red Bull chief technical officer Adrian Newey says the team are already thinking about their 2012 car, while adding that he cannot see himself working anywhere else.
Red Bull were expecting this to be a difficult weekend, believing that the track would suit the McLaren car more than theirs.
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