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" 1. Hydrogen Generators  There have been hundreds of places selling these so-called hydrogen generators, but the rush seems to have died down now that gas prices have stabilized. Prices range from a few dollars for a book of plans to make one from common household materials like a mason jar and aluminum flashing to a device that costs nearly $2000 and guarantees 100 mpg. The theory is that the free electricity can be used to electrolyze water into hydrogen and oxygen, which is in turn pumped into the engine, saving gas. We tested a couple and I worked on a story for CNBC and later for Dateline, and the results were what theory predicted\u2014it&amp;#039;s as bogus as any other perpetual-motion scam. 2. Vortex Generators  The theory is to induce a mini-tornado in the intake tract of an engine, to better mix the fuel and air for improved combustion. There are several devices on the market. We tested several, and found that they actually reduce power and increase fuel consumption.  3. Ion Generators  The Electronic Engine Ionizer is supposed to carry the &amp;quot;corona charge&amp;quot; from one spark plug to another in an adjacent cylinder, allowing the added energy to affect the incoming fuel charge and improve combustion. So we tried one. It reduced power on the dynamometer, but before we could complete the mileage run, it melted and caught fire. Postmortem examination of the Ionizer&amp;#039;s &amp;quot;capacitor blocks&amp;quot; revealed no capacitors of any sort, just molded rubber. And for the $100 price, not very well molded at that. 4. Acetone  Supposedly, adding a spoonful or so of acetone to the fuel in your tank will make it burn more completely, increasing mileage. It&amp;#039;s become an urban legend, but I&amp;#039;ve never found any evidence that it works that isn&amp;#039;t anecdotal. The theory is that the volatile acetone changes the surface tension of the gasoline droplets as they enter the cylinder to make them evaporate faster, so more of the gasoline is in gaseous form when the spark plug fires. This ignores the 400-plus-degree temperature and 250-mph velocity of the turbulent incoming air charge, and its ability to turn a spoonful of gasoline into vapor. The proportion of unburned fuel in the exhaust, pre-catalytic converter is measured in parts per million. Improving that by a huge amount would have no discernible effect on overall fuel economy. Not that any reputable engineer or scientist would suggest that acetone would do so. Downside: Acetone may damage fuel-system seals, injectors and fuel pumps.   --&amp;amp;gt; 5. BioPerformance&amp;#039;s Mothballs  (Photo by Billie Hara/Flickr) Back in 2006 BioPerformance Inc&amp;#039;s mail-order operation was shut down by the Texas state attorney general&amp;#039;s office, and refunds ordered to all its customers. The AG came to the same conclusion we had: that the product didn&amp;#039;t work. The claim was that BioPerformance pills worked by (to quote its website) &amp;quot;modifying the fuel&amp;#039;s molecular structure and liberating the energy contained within,&amp;quot; whatever that means. The product\u2014which I have a jar of here in my desk\u2014consists largely of naphthalene, the active ingredient in mothballs. Napthalene will seriously degrade the octane rating of pump gasoline, and consequently may damage your engine. 6. Ectoplasm Traps  (Photo courtesy of Columbia Pictures) I kid you not, I saw this for sale on a British website a few years back, and, thankfully, it&amp;#039;s been long gone for a while. The device itself was simple\u2014it was a coin-size metal tab coated with adhesive on one side, to be stuck to the corner of the fuel tank. The ectoplasm trap in the coin supposedly captured ectoplasmic energy, which in turn energized the gasoline inside the tank, doubling your mileage\u2014and all for only a hundred quid. 7. Fuel-Line Magnets  Farmers periodically feed small, epoxy-coated magnets to cattle to sweep any iron-based metallic foreign objects from the ruminants&amp;#039; seven stomachs. Apparently cows will ingest nails, staples and odd bits of barbed wire along with their hay if you let them. The magnet sticks to the object, and the whole business winds up in the cow patty, apparently to be cleaned and reused. Someone came up with the idea of selling these inexpensive magnets to vehicle owners. The notion is to attach the magnet to the fuel line near the engine. The powerful flux of magnetic force will, supposedly, break up the clumps of gasoline molecules and straighten them out, making the gasoline easier to burn. At least that&amp;#039;s what some of the purveyors of these devices are saying. Others say that the magnet will break up the neatly ordered rows of gasoline molecules into a more random orientation\u2014also to promote more complete combustion. Needless to say, these claims are bogus and the magnets do much better work in cow patties. These devices sell from around 10 bucks to nearly 300. 8. Water Injectors  World War II fighter pilots used water injection to provide emergency sprint power to supercharged piston engines running at high power settings at high altitude, where there isn&amp;#039;t much cooling air. The injected water evaporates, cooling the intake charge and increasing its density. The result is more power with less risk of detonation. The modern-day device we tested, the Aqua Tune, uses manifold vacuum, not a calibrated pump, to dribble water into the intake. They claim the ultrasonic chamber inside the Aqua Tune unit cracks the hydrogen and oxygen apart, making your car burn the water. (No one else seems to know how to disassociate hydrogen from oxygen ultrasonically.) The Aqua Tune we tested reduced engine power and increased fuel consumption, as well as making the truck run hot. Not to demean the concept of water/alcohol injection, which is a well-understood aircraft technology and can provide a safe power boost on highly boosted engines. But a simple vacuum-operated (although not exactly inexpensive) system has no way to add water when it&amp;#039;s needed\u2014during wide-open-throttle operation\u2014since there&amp;#039;s no manifold vacuum then to pull water in. And there&amp;#039;s little advantage to adding water when there is plenty of manifold vacuum, at part-throttle. The latest version of the device we tested now incorporates a hydrogen-generator system to boot, which sort of flies in the face of claims of being able to split water with ultrasound. "^^<http://www.w3.org/2001/XMLSchema#string>
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