With gas prices sky-high, one of the hottest trends is anything that will increase mileage and improve performance on your car. One of the most widely-touted modifications you can make to your car right now is installing a cold air intake of some kind. An article posted on the canada.com website describes the benefits of a cold air intake thusly: "The benefits of the gasoline system are increased cool-air flow for better overall power and mileage. The diesel setup increases cool-air flow twice as much as the factory system allowing the turbo to spin quicker, thus increasing boost to make more torque and horsepower. The cooler air helps increase diesel engine life. Both systems use reusable oil-impregnated filters that trap contaminants without sacrificing air flow. These filters come with a lifetime warranty. Again, the price depends on the application but starts at around $300." But, do old air intakes increase mpg? I haven't seen enough hard data to decide, but the theory seems sound. However, before installing home made cold air intakes or a name brand like a velocity cold air intake, find this out: do cold air intakes void warranty details on your car?