In the 1985 Belgian Grand Prix there was a 28-second difference between the fastest driver (Brazil's Ayrton Senna on a Lotus-Renault) and second fastest driver (UK's Nigel Mansell on a Williams-Honda) after 43 laps.
43 43 Ayrton Senna Lotus-Renault Williams-Honda 1:34:19.893 + 28.422 
