Cold Air Intake System - A Breath of Fresh Air

Street Stock racers face some unusual challenges as they prepare their cars for racing. The very nature of what they're doing-trying to build a competitive racer for little or no money out of pocket-presents a number of difficult circumstances to overcome, the least of which is developing a dependable powerplant. The idea is not to spend your way to the front of the pack, but to use your resources better than the racer next to you.

As racers work to develop power in their race engines by whatever means, the one common byproduct is heat. That's true across all racing classes, from Street Stocks to Nextel Cup. The creation of heat is, under the correct conditions, the real goal. Turn the fuel into heat, use it to make the engine produce horsepower, and wield that power to accelerate the car. It's not that complex from a high-level perspective.

As more and more tracks across the country struggle to help grow the sport by making racing more affordable, racers are trying to come up with ideas to help their engines make extra power. At the same time, they try not to draw attention from the tech guys or the competition.

If we keep our thoughts focused on what's going on in the engine, we start to see some things we can do to increase its power potential. One of the simplest is to look on the outside of the engine and develop ways to keep the air entering it as cool as possible. This helps create a dense air charge entering the carburetor. Remember, the percentage of oxygen in the air is consistent within a known range, 19-21 percent. We're talking about the total of the mixture of gasses in the air, regardless of the pressure. (For further explanation refer to the Oct. '06 article on air density, specifically "Dalton's Law of Partial Pressure.") What we can do is make the incoming air as dense as possible by keeping it as cool as possible. We want to increase the total amount of air in a given volume entering the engine.

Another way to look at this is to use something we like to call the popcorn example. It works like this: take a box and use its volume to represent the same volume of air entering the engine at a specific speed. The popcorn represents the density of the air in the box, and the denser the air, the greater quantity of popcorn in the box.

How do we as racers try to affect the density of the air as it enters the engine? We have to play the hand we're dealt. We can't simply change the density without using some mechanical devices, like turbo- or superchargers, to move a greater quantity of air into the engine, or by spraying extra gasses into the engine, as is accomplished using nitrous oxide. What we can try to control, or at the very least mitigate and do so without violating any rules, is the heat of the incoming air charge.

Temperature has a strong effect on the density of the incoming air charge. Air, like most fluids, expands as it's heated. Due to the engine and radiator pumping out massive amounts of heat, the air heats up in the engine compartment and the temperature of the incoming air can be much more than 125 F hotter than the air outside the car. This is a significant temperature increase. Aside from lowering the potential power the engine can produce, hot intake air can cause detonation, and that's not something we need to deal with. So there's a double whammy of lower power and increased possibility of detonation.