a filtration sistem that removes water debree,and air in the fuel.the air in the fuel make our engines pre detonate and lose some milage,power and cackle.in my experience my van starts faster runs smoother and the top end is incredible it seems the rpm from 1800 to 3200 has more power ,also dont have to relpace the one in the engine as often since it comes with a water separator and 2 micron filters ?about your exhaust system did you lose some milage,stay even or improve? looking to get one, but scared i might lose milage,is it diamond eye ?what diameter 3 or 4''my van is a delivery one so always loking for mpg;s ,i got my airdog 100 sistem from diesel manor great service 550$ for the complete sistem,i need to learn to atatch photos so i can show you how it looks