Last updated on .From the section Formula 1

FIA race director Charlie Whiting

Formula 1 bosses have banned the sport's latest must-have technical tweak from next month's British Grand Prix.

Governing body the FIA has written to the teams explaining how it plans to dramatically limit teams' ability to exploit exhausts to increase downforce.

Teams have been tuning engines to blow gases into the critical diffuser area even when drivers are off throttle.

Even stricter restrictions on the practice will be introduced from 2012.

BBC Sport has learned that FIA race director Charlie Whiting has outlined to the teams the limits he thinks are acceptable in using so-called exhaust-blown diffusers.

These work by directing the exhausts over and under the rear of the car's floor, speeding up and smoothing the airflow and therefore increasing downforce and cornering speed.

quote Unless the teams can show a definite major problem with the approach that means it's not feasible, the ban will go ahead.

The practice has grown increasingly sophisticated in the last year, to the point that the top teams are forcing fuel through the engines even when the drivers are off the throttle in a practice known as 'hot-blowing'.

The fuel is being burnt, increasing the energy in the exhaust and giving a lap-time benefit somewhere between half a second and a second per lap.

Clever maps prevent the engine pushing the car on in these conditions by retarding the ignition.

Whiting believes this is illegal because it is using the moving parts of the engine to influence aerodynamics and therefore, in his opinion, contravenes a long-standing rule banning moveable aerodynamic devices.

Whiting's new restrictions have set a limit of 10% of throttle when the driver has lifted off the accelerator.

He has also defined the limits of engine mapping that will be permissible, in an attempt to limit increasingly exotic and complicated engine maps.

Teams will also be restricted in what they can change between qualifying and race, although in exactly what way has yet to be fully defined.

For 2012, exhausts will have to be much longer than they are now.

Currently, the top teams are using a design where the exhaust pipe is flat and exits on top of the floor in front of the rear tyres.

From 2012, pipes will have to extend to between 330-350mm beyond the rear wheel centre line, will have to be in a space between the lower rear wing and top of the diffuser and will need to be circular in dimensions, with a vertical cut-off.

The new rule will be discussed at a meeting between Whiting and the teams at F1's technical working group next week.

But BBC Sport understands that Whiting will not shift on the major principles he has outlined.

Mercedes team principal Ross Brawn said: "Unless the teams can show a definite major problem with the approach that means it's not feasible, it will go ahead."

Brawn said he had not had time to fully digest the implications of the rules, which arrived in a letter on Saturday morning at the Canadian Grand Prix.

But he added: "In qualifying, it means a lap-time deficit of half to one second, although our race modes aren't going to be that different."

The practice was started by Red Bull's engine supplier Renault in the middle of last year, and the sport's pace-setting team is believed to be the most advanced in its exploitation of the technology.

But the ban will affect all leading teams. Only Sauber, Toro Rosso, Williams, Virgin and Hispania are not using a 'hot-blown blown diffuser. Formula 1 bosses have banned the sport's latest must-have technical tweak from next month's British Grand Prix.