Austin, Oct 24 (IANS): Ferrari drivers Sebastian Vettel and Kimi Raikkonen will have to bear 10-place grid penalties for Sunday's Formula 1 United States Grand Prix after their team decided to use an updated power unit.

Reportedly, it has always been Ferrari's plan to have a new engine for the USGP as it would allow the Italian car makers to have fresh engines for the remaining four races. It would also give them an opportunity to work on developing its 2016 power unit.

As Vettel and Raikkonen have both used up their allocated four engines this season, following an update at Monza last month, they will have to face the penalty of having a fifth one.

"We will have the hit of 10 places penalty for a new engine at this event, but it has always been the plan. It's not a big secret, no surprise for us," Vettel was quoted as saying by autosport.com on Saturday.

"The story is that this was always the plan for us to have the strongest engine available at every single point of the season. Our engine guys have done a massive job, so this should not be understood as a downside. If anything, this is very positive."

The decision was a difficult one to make for Ferrari as Vettel is still in with a chance to win the drivers' championship this year. The German is a rung below first-placed Lewis Hamilton of Mercedes but is 66 points adrift with a maximum of 100 remaining.

But Vettel believes it is better to improve the power unit, rather than focusing on his slim title chance.

"If you look at just this race isolated, it's not great news, but you have to look at the whole project, the whole season, and it was always the plan to have a fresh engine here until the end of the season," he said.

"The priority was always to have maximum power at every single race. That has been our plan and it worked very well so far. Obviously we have to take the hit here but we should take the positive which is that we were able to make big steps, rather than just (look at) the penalty."