according to manual, the 450i is 8 gallons, I have never put more than 5 in mine, even after running on empty 3 weeks, the fuel gauge must start flashing on empty when it's only down 3 gallons from full, I dunno, the tank is huge, I drive mine to the gas station occasionally, but it's out of my way, to get there, my street registration limits me to roads 40mph or less, so I can't take the most direct route, and I hate driving on pavement, it eats tires, so most of time, I add a gallon here and there out of a can, and a rarely see more than a bar or 2 on the gauge