The struggling squad will introduce a new rear diffuser, similar to that run by pacesetters Brawn, for the first time.

BMW had hoped to fight for the title this year after a brilliant 2008 season when they nearly got on terms with F1 giants McLaren and Ferrari.But so far it has been an utter disaster.

Polish ace Robert Kubica - a championship contender this time last year - has yet to score a single point.

Team-mate Nick Heidfeld has only picked up six points and the well-funded Swiss-based squad are an embarrassing eighth in the team standings.

At the last race in Monaco, Kubica retired while Heidfeld could only finish 11th.

And team principal Mario Theissen said: "Ahead of the Turkish Grand Prix our results are quite sobering.

"Nobody in the team expected the season to pan out as it has so far. After taking a forward step in Spain we were clearly off the pace in Monaco.

"To regain our competitiveness we will have to ramp up our development speed significantly.

"In Istanbul we will have the next step of our development ready and will be using a multi-stage diffuser for the first time."

The so-called double-deck diffuser, used to startling effect by Brawn, Toyota and Williams, caused controversy at the start of the season with BMW among the teams seeking to have it outlawed.

But after it was declared legal, they and others have had to hurriedly redesign their cars.

Theissen admitted BMW had been wrong-footed by this season's radical new regulations but pledged a fightback.

He said: "After three successful years, this phase is our first setback.

"But we can deal with it. We are all determined to get ourselves back among the frontrunners again."