Lifting the lid on engine torque maps

“In its simplest form, the engine torque map is a theoretical model of the engine. It represents the torque output of the engine for a given engine throttle position and engine speed,” says Renault Sport F1 engine engineer David Lamb.

Torque maps were a hot topic in July and August when the FIA made some changes to the way teams were using them mid-season. But they are the single most important map for the engineers to use for reference when trying to make sure that the engine is optimised for a given circuit, according to an interesting note put out by Renault Sport today.

A directive from the FIA around the time of the German and Hungarian Grands Prix closed a loophole exploited by Red Bull Racing and its partner Renault, to improve gas pressure from the exhaust by lowering the torque curve. As a result the Formula 1 teams are no longer allowed to change the torque maps from weekend to weekend, so the maps used this weekend in Korea are not the ultimate expression of what an F1 engine will do, even if they are still fantastically advanced,

“Prior to this directive,” says Lamb, “We would change the torque map freely to suit the climatic conditions. For example, the engines will produce nearly 10% less torque at Sao Paulo than they will this weekend in Korea due to Sao Paulo’s high altitude. By changing the torque map to the prevailing conditions the engine response will feel the same to the driver across the season. Nowadays we have to request this torque map change from the FIA, and fully justify our reasoning.”

For an indication of how sophisticated the technology is in F1 nowadays around engine mapping, Lamb explains the different ways in which the engineers can tune the map to cut cylinders in order to give the driver consistent power and feel from the engine – or driveability, as it is known,

“When the driver lifts off the pedal the engine can be either fired in four cylinders or fully cut, depending on the level of overrun support he requires,” explains David. “When the driver goes back on the pedal from full ignition cut, you need to inject more fuel than usual to ‘wet’ the engine. Inject too little or too much and you will have a torque deficit from target, which can cause a hesitation and a loss of lap time. The initial torque demand will generally be met with only four cylinders, as you’d rather save a bit of fuel and have four cylinders firing strongly using a more open throttle than have eight coming into life rather weakly with a relatively closed throttle.

"When the torque demand exceeds that which can be met with just four cylinders, the remaining cylinders need to be fired. These will also require ‘wetting’. At this point you also have to close the throttles at a rate which coincides with the final four coming back into life – this is the tricky bit! Get it right and the driver should feel nothing across the transition, just a change in engine pitch. In all cases, the torque map is used in conjunction with other settings to govern both the fuelling requirements and throttle position."