mileage was very adversely affected by the smog crap. Folks that re-build it right with rv type grind, performer intake, 4bbl, straight up timing etc get better mileage and 400-420 ftlbs with about 300hp (thats not bad for an rv grind-((ie stroked cleveland)). I'm building mine specifically for propane with roller cam, full roller rockers, closed chamber heads and the highest compression I can run with a semi rv grind (214/218 duration @ .050) and still get dynamic compression below 9:1 for a semblence of longevity. Looking at close to 400hp 430+ftlbs and, hopefully, decent mileage. well see. It's odd with operating compression similar to race engine but with mileage cam...love that octane.