Well the mpg #s check out with simple division of trip miles divided by my 15 gallon tank. The thing you need to remember is i picked the powerdyne because of the impeller design which actually grabs the air and pulls it in. So even when i am running in vacume the air intake is more efficient than before. If you get a chance check out powerdynes site and read up on their impeller design. AS for mpg before s/c i averaged around 18mpg city. My intake adn exhaust kits kicked that up about 3mpg over stock.