The FIA has banned the use of engine settings that, in slow sections of the track, artificially increase engine revs and maintain exhaust output through blown diffusers. This is the cause of the distinctive ‘rough sounding’  engine note in slow corners.

With a blown diffuser, the exhaust gases are routed into the ‘coke-bottle’ shape at the rear of the car and through into the diffuser – the upturned part at the back of the car’s floor. The effect of this is to reduce air pressure underneath the car which increases aerodynamic downforce at the rear. It has proven to be a a crucial area of a F1 car’s overall aerodynamics and teams believe that the blown diffuser can provide a gain of about 0.5 seconds per lap.

The change, implemented very shortly before qualifying means that the change will require many compensating setup changes potentially leading the cars to unstable setups for the race weekend. RedBull and McLaren are less than happy.

UPDATE: The Rule has now been applied for the British Grand Prix only. For subsequent races the regulations be reversed back to the ‘valencia specification’ that permitted blown diffusers.