My300E is a manunal trans, so is probably not indicative for most of the rest of you. It gets 27 to 28 on the highway and around 20 stoplight to stoplight. There is about a gallon or a little more when the reserve light comes on and it has about a 17.5 gallon tank I think.

The cyclone gizmo on SOME carbureted engines could in rare instances improve, probably immeasurably, fuel mileage. This is because in a carbureted engine the fuel is mixed with the air and sometimes does not atomize properly. This means that the fuel sometimes flows in droplets rather than a mist. In some cases this gizmo could mix the fuel causing more complete combustion.

In a fuel injected engine, the air flows by itself until the very end of the intake runner where the fuel is injected as a mist in the airstream. In this case, which covers most all cars built in the last fifteen years or so, the cyclone does just as Freestyler says, they only inhibit air flow.

They are snake oil and the folks who sell them should be ashamed of themselves.

Have a great day,