The devices were tested on 4 full size trucks... We strapped the trucks down to a paif of chassis dynamometers and ran them dry of gasoline. then we added a measured quanity of gas, and ran four dyno pulls to determine horsepower and torque. Next, we accelerated to a corrected 70 mph, set the cruise controlto keep the speeds consistent and ran the trucks dry again. This gave us a base line of each truck's unmodified power and fuel consumption.
results

Miracle magnets.
Fuel Saver, Fuel OptiMiser
>JC Whitney, $22;heartlandamerica.com, $20
>THEY CLAIM: It magnetically rearranges gasoline molecules for better combustion.
> BOTTOM LINE: Weird science, but at least it can't hurt.

The Dyno says. As we suspected, neither device had any significant effect on performance or economy.

Vortex Generators.

Intake Twister
>ebay, $20
>THEY CLAIM: "Increase your gas mileage buy [sic] 5-10 mpg and increase your hp by up to +10 hp." "Spreads the gas out to get a full combustion."
>BOTTOM LINE: Doesn't work and could fail and damage expensive parts.

TornadoFuelSaver
>TornadoFuelSaver.com, $70
>THEY CLAIM: ">>> an increase in gas mileage-up to 28%!!!" "Dynamometer [sic] testing demonstrates an increase of 4-13 horsepower."
>BOTTOM LINE: Normally, we want less turbulance in the intake, not more.

The dyno says:Both devices reduced peak horsepower by more than 10 percent. The Intake Twister increased fuel consumption by about 20 percent; the TornadoFuelSaver provided no significant change.