Complex sentence: All cars ran on Sunoco 260 GT Plus, a 104-octane (R + M/2) unleaded racing fuel, the fuel which NASCAR planned to use throughout the 2007 season.
Split into simpler sentences: All cars ran on Sunoco 260 GT Plus, a 104-octane (R + M/2) unleaded racing fuel. This is the fuel that NASCAR has planned to use throughout the 2007 season.