Following an enquiry by the Williams F1 team the FIA have announced that their interpretation of the F1 Technical Regulations are such that the engines should not blow gases through the exhaust systems in such a way that provides an aerodynamic advantage. The effective banning of off throttle blowing is to take effect from the 2011 British Grand Prix and the technical regulations will be changed for 2012 to specify the location of the exhaust pipes so that the exhaust gases cannot influence the diffuser.
While the concept of blowing exhaust gases through the diffuser at the rear of the car has been in place for a couple of decades, there has been a recent spurt in expanding the use of the exhaust gases. This is achieved via one of two approaches, or at least, how I understand these approaches to work.
The first, and most common approach has been termed "cold blowing" and is achieved by allowing exhaust gases to continue flowing at a higher than normal off-throttle rate by maintaining the throttle body in an open position after releasing the throttle pedal. The fuel is cut as the throttle pedal is released, thereby allowing cool air to flow through the engine. Cold blowing has the advantage of maintaining a lower engine temperature which aids engine reliability.
The second approach, coined "hot blowing", is an extension of cold blowing where the fuel mix continues to flow through the cylinders but the spark is delayed until the exhaust valves are open so as to push the exploded gases through the exhaust system. This approach seems to be particularly offensive to the FIA as the resulting increase in fuel usage flies against the green goal that the FIA is trying to promote through devices such as the KERS hybrid.
The FIA have referred to Article 3.15 of the Technical Regulations in their discussions, suggesting that this regulation is arguably being breached by the use of blown exhaust systems. Article 3.15 states:
With the exception of the parts necessary for the adjustment described in Article 3.18 (DRS moveable rear wing), any car system, device or procedure which uses, or is suspected of using, driver movement as a means of altering the aerodynamic characteristics of the car is prohibited."
This part of Article 3.15 was added in 2011 in order to ban the use of the blown rear wings that came to prevalence in 2010. These devices required the driver to use a part of their body to block a hole in the footwell or elsewhere in the cockpit that resulted in airflow being diverted to the rear wing.
The blown exhaust is effected by the driver lifting his foot off the throttle pedal and the engine mapping in the ECU selecting the timing of the spark, the amount of fuel and the amount of air at each engine revolution rate. It is clear in the case of the blown rear wing that driver movement is used to alter the aerodynamic characteristics of the car as the driver was required to make a specific movement to block a hole. It is not so clear in the case of off-throttle exhaust blowing. The question is whether the simple and necessary act of lifting off the throttle is a driver movement used to alter the aerodynamic characteristics of the car.
One can see that the FIA may have an argument, as the off-throttle exhaust blowing can only exist where the engine is running down after a throttle application. Given that the throttle application is a result of a movement of the driver, it seems that the FIA argument may be successful.
However, the action of the driver either pressing or lifting off the throttle changes the aerodynamic characteristics of the car as these change as the car increases and decreases in speed. The driver pressing the brake or turning the steering wheel will also change the aerodynamic characteristics of the car. Consequently, the FIA argument is flawed and if the argument is successful would lead to the car being unable to move in any direction without breaching Article 3.15, making racing more than a little difficult.
Given that the FIA consider the off-throttle blowing to be a breach of the current regulations, the teams can choose to change their throttle maps or run the gauntlet and keep their existing maps. Some of the teams may be ready to run the risk of being excluded from the race by the stewards, however given that the stewards would be ruling on what is a pretty grey area, they are more likely to refer the issue to the World Motor Sports Council (WMSC) for their ruling. The stewards should take this approach and allow the WMSC to determine the appropriate interpretation of the rules.