James Allison: Renault may suffer less under exhaust ban

Renault technical director James Allison suggests that his team could lose out less than others in the Silverstone exhaust clampdown because the team’s side exit design means that the car’ aero balance will change less.

Allison is the first technical director to give a detailed explanation of what the Silverstone rule changes – a ban on using engine mapping for aerodynamic effect – will mean for the teams. He also confirms that from Valencia teams will not be able to change maps between qualifying and the race.

“The FIA’s note will cause all teams (whether or not they use a blown floor) to change their operation,” said Allison on the team website. “The headline changes for the Silverstone GP are as follows: when the driver lifts his foot fully off the throttle pedal, then the ECU maps must be set up so that the engine [to all intents and purposes] closes the throttle – previously it was possible to configure the engine maps to leave the throttle open and reduce the engine power by other means.

“Furthermore, when the driver lifts fully off the throttle, the ECU maps must be configured to cut off the fuel supply to the engine – this is intended to prevent so called “hot blowing” where the energy of the exhaust gas is increased by combustion.

“Finally, with immediate effect, it will no longer be possible to reprogramme the ECU configuration between qualifying and the race in the expectation that this will discourage extreme ECU setups for qualifying – previously electronic access to the ECU under parc fermé conditions had been explicitly permitted.”

Discussing the specific impact on Renault, Allison said: “It is not easy to judge the effect of this change on our competitiveness. The loss for each blown floor car will come from two separate effects – how much downforce will you lose and, in addition, how much will the loss of this downforce upset the balance of the car.

“All blown floor cars will lose downforce under braking as a result of these new restrictions. Some teams will lose more and some teams less; it is hard to know exactly what relative loss LRGP will suffer. However, it is possible that we will suffer less on the balance shift side of the equation because our forward exit exhausts produce their effect quite near the middle of the car.

“This means that as the exhaust blow waxes and wanes, it does not really disturb the aero balance of the car too much. With a rearward blower, the downforce from the exhaust is all generated at the rear axle. As the new rules reduce the blowing effect on corner entry much more than corner exit, it is possible that the rearward blowers will tend to suffer more nervousness under braking and more understeer on exit as a result of the new restrictions. We will find out at Silverstone!”