Force India disappointed by delay in Mercedes F1 engine upgrade

The team expected to receive the upgraded engine, which is already being used by works drivers Lewis Hamilton and Valtteri Bottas, at last week's Belgian Grand Prix.

Green says both Force India and Williams were originally told they would receive the upgrade at Spa, but manufacturing issues led to the delay.

Mercedes treats its customer teams equally and each team will receive one upgraded engine for the Singapore Grand Prix in two weeks, which adds the complication of Force India and Williams having to give it to only one of their drivers.

"One in Singapore is what we're promised at the moment," said Green.

"We were originally told we would get it in Spa. There's some disappointment.

"It's always useful having more horsepower, that's for sure, so it would have been nice to have had it at the two most power sensitive tracks that we go to.

"Are we happy that we're one power unit less than the works team? No, we're not."

"We'd rather be in their situation. It's a performance upgrade, and given that these were the two most power sensitive tracks during the season [Spa and Monza], these were the two races where we would have really liked it."

Green said it was "unprecedented" for Mercedes to provide only one example of an upgrade to each customer team.

The later introduction of the engine means Force India will have to run at the 0.9l/100km oil burn limit that has come into force this weekend.

But Green says there's no question of it missing out on any advantage Mercedes has gained by introducing the works engines at Spa and being able to run at the old limit of 1.2l/100km.

"We don't see that as a big issue," said Green. "The latest power unit we're told is well within the new oil consumption limit.

"We're taking the same hardware, after the cutback in the oil consumption. We would expect it to be compliant, and it is."

Force India COO Otmar Szafnauer explained that Mercedes had been cautious in releasing the new engine to the customer teams because of reliability fears after some "manufacturing quality issues".

He confirmed that usually the driver ahead in the championship - currently Perez, who has a nine point advantage - would get any new parts.

But he hinted that the drivers also have to behave themselves in the Monza race after recent clashes or risk forfeiting that opportunity, even if they finish the weekend in front.

"In the past it's no secret that our rules of engagement, and most teams do the same, is that the guy ahead in the championship gets the one that we have," said Szafnauer.

"It will be who helps maximise the team's points that gets it."