Ferrari are amongst many teams that have placed their exhausts down low close the cars centreline. In doing this they are passing some of the exhaust gas through the starter motor hole in the diffuser to create more downforce. This solution was likely given the cars exhaust and diffuser layout, but was proven when Felipe Massa’s fire on the third day of testing showed the flames passing not only over, but also through diffuser via the starter hole. Given the rule changes this year, this solution is surprisingly legal.
Teams were using this legal opening in the diffuser last year for aiding their double diffusers. Using the opening as an extra slot to make the diffuser more aggressive, just as rear wings use more slots to allow them more angle-of-attack. Mid season in 2010 the FIA issued a clarification to reduce the size of the slot. This formally made it into the technical regulations for 2011 as article 3.12.7.
3.12.7 An aperture for the purpose of allowing access for the device referred to in Article 5.16 is permitted in this surface. However, no such aperture may have an area greater than 3500mm2 when projected onto the surface itself and no point on the aperture may be more than 100mm from any other point on the aperture.
It doesn’t state or prohibit what else the aperture can be used for, just its maximum surface area and width can be. A rectangular slot would be 10cm wide and 3.5 cm tall, a simple round hole would be a 66mm in diameter.
As the FIA moved to prevent double diffuser, the loophole allowing opening the floor was also closed to the kind of open fronted diffuser as used by Red bull and latterly many of the top teams. With this change in the rules teams are limited in how they can blow the exhaust into the diffuser. Aside from Red Bulls exploitation of the outer 5cm of floor, the only other option is to blow some of the gas through the starter motor hole.
By pointing the exhausts along the sides of the gearbox the fast moving gas flow will pass over the top of the diffuser, when it hits the trailing edge and gurney flap it will help draw more flow underneath the diffuser.