MotoGP Blog

Changes to the MotoGP rulebook in 2007 modified the engine capacity to 800cc and reduced the maximum fuel capacity of the bikes to 21 litres. In 2008, the paddock has twelve months experience with these restrictions and the factory engineers in the off-season have embarked on a quest to dramatically increase the power outputs from the engines. The goal: to catch Ducati, Ducati’s goal being to at least maintain the power advantage.

The search for increased power within the engine capacity limitations has led to higher revs. This in turn means higher fuel consumption. This gives the engineers a dilemma: more power is required, but the amount of fuel is fixed. Each drop of fuel now has to be carefully managed from tank to cylinder to combustion to ensure the maximum power is derived from the 21 litres that start the race.

This fuel management is achieved through what is known as a fuel mapping. The on-board electronics take measurements of several key factors in deciding how much fuel to inject into each cylinder, to provide the rider with the power (or lack of it) he is indicating with the position of the throttle grip. These factors will include, but are not limited to:

• throttle grip position,
• engine RPM,
• engine load,
• air temperature,
• engine coolant temperature,
• atmospheric pressure.

All of these factors are taken account of when choosing how long a pulse of fuel to deliver to each cylinder - the longer the pulse, the more fuel is delivered. A collection of pulse values for every combination of factor values is known as a fuel map, often shown in the form of a graph (right). The ECU (Engine Control Unit) reads the factor values from the sensors around the bike, consults the map and chooses the pulse duration. Different fuel maps can be tuned to deliver different characteristics such as peak power at the top of the rev range, low rev torque for starts, a standard mode delivering as much power as possible while using as little fuel, or anything in between. The real advantage comes when the rider is able to switch between fuel maps to select the most appropriate map for the conditions, or for what he needs to achieve at a given point in the race.

What we may have seen for the first time in 2008 is a dynamically modified fuel map, meaning the electronics can switch or even adapt the selected fuel map to modify the fuel consumption of the bike to ensure it finishes the race. Think back to Casey Stoner and Dani Pedrosa in Qatar 2008, running out of fuel on the slowing down lap - that is ECU fuel management at work.