The car Bibles product reviews: The Tornado Fuel Saver.
Product Reviews
The Tornado Fuel Saver
Tested March 2006 
The Tornado is in a class of device marketed through scare tactics and confusion. It is marketed under many names including Vortec Cyclone, Vortex, HiClone and Tornado.. With climbing gas prices, the manufacturers of such devices will attempt to lure you in with promises of better fuel economy, more power, less engine wear and so on and so forth. The Tornado comes in a pretty shabby cardboard box along with an instruction / installation sheet. The Tornado itself is made of fairly lightweight pressed steel or aluminium and has some sharp edges on it. Fitting it was pretty easy; unclip the cold-air intake, pop in the Tornado, clip it back together and away you go. The test vehicle was a completely stock 2001 Subaru Impreza RS. The vehicle regularly returns 25.9mpg on the freeway. I tested the Tornado on a trip to Vegas and back - a 900 mile round-trip, as well as week's worth of testing around town on the daily commute. I filled up the vehicle at the usual gas stops from the usual pumps. We do the Vegas trip a couple of times a year so I have a good set of data points for how the Subaru performs. I calculated our fuel efficiency based on reported mileage on the odometer vs. reported gallons in the tank (from the pumps) which is the same technique I use every time I do this. On the way down to Vegas, our gas mileage dropped to 22mpg and on the way back it was about 21.5mpg. The average for this trip was 21.75mpg, down from the usual 25.9mpg. Around town, the Subaru normally manages 21.9mpg. After a week's use with the Tornado, my average gas mileage was 21.8mpg - near enough the same.
Conclusion? On long motorway hauls, the Tornado absolutely does not help. In my test it actually made the gas mileage worse, which in the days of $3/gallon petrol is nothing to be laughed at. Around town it made a negligible difference. I'd say Don't was your money on this thing except I managed to flog mine on e-bay so evidently people are still buying them.
Note: I was so underwhelmed by the results that I didn't bother dyno testing the vehicle to see if the claims of improved power were true or not.