Colder is Better
While reading through the last few columns of Tech Center, you may have noticed a trend relating to cold air. Specifically, colder is better. When discussing the function of drum and disc brakes, it was stated that disc brakes are superior because they dissipate heat more rapidly, thus keeping the brake system cool and providing improved stopping power. A similar statement was made in regard to turbocharging, in which an intercooler is used to cool the compressed air after it leaves the turbo and before it enters the intake manifold. Finally, in our column discussing the workings of nitrous oxide, a specific mention was made about the tremendous "cooling effect" nitrous oxide has on the intake charge and why this effect helps increase horsepower.
With all this cold air blowing around, it might sound like we should just pack our bags and move to Fairbanks, Alaska, so our cars can finally operate at peak efficiency. From a pure automotive performance standpoint, it's not a bad idea. But it's tough to enjoy serious automotive performance in such a snowy climate (not to mention the dreadful guy/girl ratio up there), so a less drastic alternative seems in order.
One of the more common methods of improving vehicle performance, with regards to cooler temperatures, involves directing cold, outside air into a vehicle's engine compartment. This differs from the use of intercoolers in the sense that an intercooler is a container, much like a radiator, that passes air through it to reduce the temperature. In a cold-air system (or fresh-air system as they are sometimes called) a passageway (or series of passageways) is used to provide a cooler, oxygen-rich air charge to the engine. In an ideal system, the air is funneled directly into the engine's intake system for maximum efficiency.
As with the intercoolers used on turbocharged vehicles, the cooler outside air offers a more dense mixture of oxygen and a more powerful explosion when combined with fuel. It's this promise of increased horsepower that compels many current street racers to either hack open their hoods or to purchase aftermarket hoods with a "scoop" already installed. This is somewhat laughable since the use of cool air for increased horsepower has become standard procedure for new cars and is already utilized on most models, whether performance oriented or not. Though it rarely involves a hole in the hood, close inspection of the lower grille or bumper area will often reveal an opening that feeds into a system of pipes and eventually stops at the intake manifold. There are exceptions, of course, like the last Camaro SS with a hood that bumped performance (both perceived and actual) with its gaping maw.
An interesting bonus to cold-air induction relates to its effect at higher speeds. Depending on the location of the initial opening and the efficiency of the system, it's completely possible to get a "ram" effect from the force of the incoming air. In other words, at higher speeds the incoming air will actually start to compress in the combustion chamber during the intake stroke, creating a supercharger-like effect. (This ram effect is the basis for the "Ram Air" nomenclature that has been used on performance Pontiacs since the late 1960s.) No, you're not going to see a 30-40 percent increase in power just by letting cold air into the engine compartment and driving 100 miles-per-hour. However, an effective cold-air system can improve quarter-mile times by as much as three-tenths of a second; not a bad result for just letting some cool air into the engine. And since cold-air systems involve no drain on the engine, unlike turbochargers and superchargers, they cause no reduction in gas mileage or increased engine wear. Except for the small cost to design and install the cold-air piping, it's about the closest thing to free horsepower you'll find on modern automobiles.
Like we said, colder is better.