In August 9, 1975, Mark Donohue drove a 917/30 at an average speed of 353.84 km/h (221.160 mph) at the Talladega Superspeedway, in Alabama, USA.
Nowadays the record belongs to Gil de Ferran. In 2000, aboard a Penske Reynard-Honda, he reached an average of 386.285 km/h (241.428 mph) at the Auto Club Speedway in Fontana, California.
But Donohue’s car was MUCH cooler.