The theory behind Tornado intakes is sound: Creating a vortex of swirling air in the intake can better dissolve fuel droplets in the airstream, leading to greater power and fuel economy. Older carbureted and throttle-body injected engines have seen some gains with this type of enhancement.

On the Other: It Doesn't Work

Modern engines almost exclusively use multipoint or direct-injection systems. These systems place the fuel injectors either inches from the intake valve or inside the combustion chamber. As such, it wouldn't matter if there were an F5 stampeding through your intake; there is no fuel to mix. Aside from that, these "tornadoes" disrupt and limit airflow, which can lead to a decrease in power and fuel economy.

Bottom Line

According to both Consumer Reports and CarBibles.com, "vortex generators" are snake oil on most engines. CarBible's test reported a loss of 4 mpg on a stock Subaru Impreza, and CR reported no gain or loss whatsoever on its Ford Ranger. CR's similarly tested Volkswagen New Beetle experienced a noticeable drop in power with the Tornado, and no improvement in fuel economy.

Source:

Consumer Reports: Gas-Saving Devices

Carbibles.com: Tornado Reviews

OffRoaders.com: Reviews

Resource:

Tornado Test News Report (Video)