Grab a copy of this months Popular mechanics. They tested the top ten "Miracle gadgets" out of 300 on the market. It was just flat out hysterical just how sad theese things are.
http://www.popularmechanics.com/automotive/auto_technology/1802932.html
As long as there have been cars, there have been gadgets that promise revolutionary improvements in performance and mileage. And every time there's a spike in fuel prices, these gadgets proliferate like mushrooms after a spring rain. Like now, with crude oil over $60 per barrel. Scan the Internet, store shelves and, yes, even the classified ads in the back of PM, and you will find dozens of devices promising to boost power, reduce emissions and, of course, improve mileage by 20, 40, even 300 percent!
Hey, we're not gullible. But we're not close-minded either. Could it be that the basement tinkerers behind most of these products have stumbled upon some heretofore undiscovered principle of physics or thermodynamics? Is it possible that the major auto companies have overlooked--or deliberately avoided--simple engine modifications that would give their cars and trucks an overwhelming advantage in the marketplace? Instead of dismissing such far-fetched notions out of hand, we decided to give the gas-gadget makers a chance to prove their miraculous claims.
We purchased seven typical gadgets--ranging in price from $20 to nearly $400--representing the most common approaches used by devices claiming to boost mileage, such as applying magnets to the fuel line, modifying air intakes or injecting extra fuel into the engine.
We conducted our tests at the Universal Technical Institute, a large training facility for automotive technicians, in Houston. We chose four full-size pickup trucks from UTI's fleet as our test vehicles. Why pickups? Well, for one thing, the pickup truck tends to be the poster child for conspicuous consumption of Mideast oil. Also, truck engine compartments are roomy enough that we could install the products without feeling like we were assembling a ship in a bottle.
We strapped the trucks down to a pair of chassis dynamometers and ran them dry of gasoline. Then we added a measured quantity of gas, and ran four dyno pulls to determine horsepower and torque. Next, we accelerated to a corrected 70 mph, set the cruise control to 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.
We gassed up the trucks, installed our gas-savers and repeated the tests. (We didn't check for emissions, figuring most people who buy these products are fighting a holding action on their wallets, not on the environment. ) Here are the gadgets and how they performed.
MIRACLE MAGNETS
There are dozens of fuel-line magnets on the market. We tested two. They all make similar claims: substantial improvements in fuel economy, reduced emissions and increased horsepower.
According to the people selling these devices, as gasoline flows past the magnet, the magnetic field will "break apart clusters of fuel molecules so gas burns more efficiently. " Problem: Gasoline molecules aren't magnetic, not at all. But wait, there's more. If the fuel line is steel, as many are, the lines of magnetic flux will follow the fuel line walls instead of passing through the fuel.
THE DYNO SAYS: As we suspected, neither device had any significant effect on performance or economy.
VORTEX GENERATORS
These devices, which are usually installed on the upstream side of the mass airflow (MAF) sensor, use stationary vanes or, on some devices, spinning blades to make the inlet air between the air cleaner and intake manifold whirl around in a mini-tornado. This vortex supposedly mixes fuel more thoroughly with air, which means the fuel will, theoretically, burn more completely in the combustion chamber. Trouble is, there's a lot of intake tract downstream from these devices designed to maximize a smooth airflow. Turbulence, coupled with the restricted airflow caused by the device, can only reduce the amount of air sucked into the manifold. Less air means less power.
Again, we tested two devices. The TornadoFuelSaver is a nicely made stainless steel contraption, available in an assortment of sizes to fit most vehicles. We installed it on our truck's intake tract immediately upstream of the MAF sensor. We purchased the second device, the Intake Twister, on eBay. It was crudely handmade from sheet-aluminum flashing and pop rivets. It looked like something we could make in about 10 minutes from an old soda can. The staff at UTI was reluctant to install it: The bent sheetmetal vanes looked as if they might break off and be digested by the engine. The device is one-size-fits-all, and is simply bent into a curl to insert it into the intake duct.
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. 
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