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Formula 1's competitive order at the front of the field could be thrown on its head in this weekend's Spanish Grand Prix with the FIA having made a major change to the exhaust blown diffuser regulations, AUTOSPORT has learned.

With the design and execution of blown diffusers being viewed as a key area of the 2011 development race, teams have been pushing hard with their concepts to try and eke out any competitive advantage they can.

One aspect that has been worked on a lot is in ensuring that a flow of exhaust gases keep pumping through the diffuser, to help increase downforce, even when the throttle is not in use.

But now, on the back of some teams expending huge effort in tweaking engine modes to help gain performance in this area, the FIA has acted and decided to clamp down on what they are up to.

High level sources have revealed that the FIA has written to teams informing them that from this weekend's Spanish Grand Prix they will no longer be allowed to continue flowing gases through the engine when the driver is not on the throttle.

It is understood the directive to the teams tells them that, under braking, the throttle input can now be no larger than 10 per cent of its maximum. Some outfits had been gaining aerodynamic benefit from keeping the throttle flow at 100 per cent under braking.

To push this regulation change through, the FIA has deemed that throttle use will be allowed only for the purpose of increasing torque, not for 'aerodynamic performance'.

This effectively means that any team found to be using off-throttle blown diffusers could be in breach of the famous Article 3.15 of the technical regulations that outlaws moveable aerodynamic devices.

The change in regulations is set to hurt every team running a blown diffuser - although some may be hurt more than others.

Mercedes GP team principal Ross Brawn said: "It will affect all the teams. These staccato exhausts you hear, I don't think you are going to hear them anymore.

"The teams have all been developing their engine management systems to get the maximum advantage from the exhausts, and the FIA want to push us in a different direction now so there will be changes there.

"I've no idea what will be the outcome there, but it has forced all the teams to have a fresh look at what they are doing in terms of engine strategies."

However, with McLaren having recently hinted that it viewed off-throttle engine maps as a key to Red Bull Racing's qualifying form, the change in regulations could mean the reigning world champion team is one of the worst hit.

Speaking to AUTOSPORT about the impact of the change in rules, Red Bull Racing team principal Christian Horner said: "I think that it is going to have an effect with all teams that have been utilising it.

"That appears to be 90 per cent of the grid, if you look at how many teams are running blown diffusers. It is not something unique to this year, it is something that started last year, so Barcelona will clearly show what effect this will have."

When asked if he thought the rules change had come about as the result of a complaint from a rival team to try and slow Red Bull Racing down, Horner said: "It is inevitable and the unfortunate consequence of success."