This is the first thing just about anyone will tell you when you say you want to up your horsepower. It's kind of like those minty-fresh gum commercials with the ice swirling around, and the price is only a smidge more than a pack of gum. A kind of big smidge, but still. The idea is that cold air is more dense, so more air gets into the cylinders to mix with the fuel. More air means more combustion, and more combustion means more power, to the tune of a realistic 5- to 7-horsepower in a typical engine. This only works if the air intake is the limiting factor, however. If your engine is already sucking in big breaths of cool, fresh air, then try one of the other tricks on this list.