Brian, mileage, in hot rod terms, is variable to the car the engine is in. Unless you find someone running the exact combination you plan to run, mileage figuires are worthless. A '55 Chevy with a Ram Jet will not get the mileage a Duece with a ZZ4 and a carb simply from a weight stand point (and aerodynamic for that matter). A computer controlled engine, all things being equal, will get better mileage than a carburated engine. Will the close loop system increase your mileage and performance? Yes, but will the mileage make up for the cost driven on a part time basis? Over time yes, but the time will vary by the amount the vehicle is driven.