I was on a 50% race and had a terrible qualifying round, starting from a full grid and in last place. I decided to run the first stint on Prime tyres. I then started out the race using low revs to build up some fuel reserves. After about 4 laps, I had gained an extra 3 laps of fuel. I was in a reasonable position by this time, so stayed on low revs, hoping to gain some extra fuel, however after a further 5 laps of racing on low revs, I was still on only +3 laps of fuel. For a total of 8.5 laps. What then further surprised me is that a couple of laps later, I attempted an overtake, so put the car into high revs and was in this mode for what must be no more than 1/2 a lap and as soon as I crossed the line, I was down to only +2 laps of extra fuel, despite spending a total of at least 8 laps of low revs. I am certain that the maximum extra fuel is +3 laps.