Complex sentence: Cars in this category were previously heavily modified versions of road cars, usually supercars such as the McLaren F1 and Ferrari F40, but when the 911 GT1 was uneveiled in 1996 Porsche had exploited the rule book to the full and stunned the sportscar fraternity.
Split into simpler sentences: Cars in this category were previously heavily modified versions of road cars, usually supercars such as the McLaren F1 and Ferrari F40. However, when the 911 GT1 was uneveiled in 1996, Porsche exploited the rule book to the full and stunned the sportscar fraternity.