I just drive until I need gas, fill up, drive like H***. Gas mileage is anything from 8 to 23 depending on my mood. With the LS1 and 36 lb injectors, cam, 90mm TB all it takes is a couple of hard runs to 100 and you can watch the gauge go down. It takes fuel to make power, and I run it a little rich on purpose (Flash Scan Tunning).