Blown diffusers - So what exactly is being banned?

The Formula 1 teams have been on notice for a few weeks that the practice of "hot blowing" and "cold blowing" exhaust through the diffusers is to be banned and yesterday the FIA confirmed that this would take effect from Silverstone onwards.

Meanwhile the whole concept of blown diffusers will be banned in 2012 as new rules will insist that the exhausts exit out of the back of the car, as in the past.

The Technical Working Group, which consists of the FIA's Charlie Whiting and engineers from all the teams, will meet this week to decide exactly how to frame the wording of the ban so it is policeable.

But what exactly is "hot and cold blowing" and what is being banned here?

Cold blowing - When the driver lifts off the throttle pedal the engine throttles go to 100% and it cuts all the fuel to the spark, so there is no drive from the engine but all the air is flowing through the engine to give about 75% of the exhaust pressure you get on the power. Everyone has been doing this for the last 12 months.

Hot blowing - For the last two or three months this practice has come in. In hot blowing they start to inject some fuel and put a spark into the engine to increase the energy into the gas. So they end up with more downforce. To do that they have to retard the ignition and kill the torque, because if you don't then the engine is going to create torque and the engine is going to keep going when the driver lifts off the throttle.

The performance gain is around half a second to one second per lap. But this drives fuel consumption up by around 15% and is very hard on engines, so it means costly reliability programmes. This is not the way the FIA wants the sport to go.

The question everyone wants to know is, will this slow the Red Bulls down relative to the opposition?

Renault, Red Bull's engine supplier, has been working on this technology for longer than the others, but Ferrari and Mercedes are very active in this area too. The majority of Red Bull's advantage is the power of its DRS wing, which can be used in fast corners and gives it a couple of tenths of a second in qualifying over McLaren in particular and also Ferrari. In the race this advantage goes because the DRS can only be used on a straight and when following another car. Hence why the races are much closer than qualifying.

Hot blowing is something Cosworth haven't been engaged in, so teams like Williams can only do cold blowing.

Fans at Silverstone, who have already attended a race this season, will notice the absence of the distinctive crackle sound when the driver lifts off the throttle.

The FIA's memo to the teams, issued on Saturday in Montreal, makes it clear that the reason for the move is that the direction these devices are taking the sport is completely opposite to what the federation is trying to achieve.

The memo says, "The financial, technical and human resources required to support such developments, as well as the impact on engine reliability and on fuel consumption are totally contrary to the objectives pursued by the FIA, the teams and the engine manufacturers."

For next year exhausts will go back to looking conventional, they will have to extend to between 330-350mm beyond the rear wheel centre line, be situated in the area between the bottom of the rear wing and the top of the diffuser and have to be circular, with a vertical cut-off.