S&B Filter's commitment to the race community allowed us to develop products that featured incredibly high efficiency ratings and tremendously low airflow restriction. Exceptional design, leading-edge manufacturing and a commitment to thorough research and development, has allowed them to make several advancements within the high performance category. S&B test their products to a higher standard in order to develop intake kits that improve airflow, protect the engine and permit more horsepower for your Dodge Cummins, Ford Powerstroke, and Chevy/GM Duramax truck.
All combustion engines utilize air and fuel to generate power.
Simply stating, increasing the amount of air entering the engine will result in an increase in power output. There are two ways to increase the amount (mass) of air consumed by the engine: increase the volumetric airflow, or increase the air density. Modifying the engine to increase the displacement, or swapping out camshafts, are a couple ways to increase the volumetric airflow (CFM) that the engine consumes. The other way to increase engine power, by increasing air density, is what we will discuss in this article. (There is a relationship between air pressure and volumetric airflow involving volumetric efficiency, but that is outside the scope of this article). Air density is predominantly controlled by temperature and pressure. (Humidity has a small effect on air density as well with humid air being less dense than dry air).
Air Density and Temperature
One can determine how a reduction in temperature increases air density by using a simple formula that takes the absolute air pressure and divides it by the temperature and specific gas constant. We used the standard sea-level pressure of 14.7 psi, and a specific gas constant of 53.35 to give us the graph (below). You can see that air density decreases as temperature increases.
When it comes to intake design, you simply want to pull in the coldest air possible for maximum air density. If the intake is pulling in warm air from inside the engine bay, the loss in air density will result in a loss of engine power. Many modern stock OEM intakes do a pretty good job of drawing cool ambient air from places such as the fender well or the front of the vehicle. It’s important for an aftermarket performance intake to pull cool ambient air from these same sources and to have a proper seal to prevent hotter air from the engine bay from leaking in.
Air Density and Pressure
If the temperature of the air pulled in by the S&B intake is the same as stock, isn’t the air density the same? No, because air temperature is only one part of the equation. Assuming that the S&B intake and stock are pulling in the same temperature of air, the air density isn’t necessarily the same.
Greater air density can be achieved when air pressure is increased. Most auto manufacturers are more concerned with noise reduction and serviceability with respect to their intake system than they are with maximizing the air pressure. Thus, by redesigning the intake to minimize airflow pressure loss, we can dramatically improve the air density fed to the engine.
Restriction is the measurement of pressure loss through the intake system. For example, when we say “the intake has 14 inches of restriction at 600 cfm,” the “inches” is referring to “inches of water,” which is a unit of measurement of pressure. Inches of water can also be expressed as pounds per square inch, or “psi.” For reference, 14 inches of water is roughly equivalent to 0.5 psi. It is just as correct to say “the intake has 0.5 psi of restriction at 600 cfm.” The conversion from inches of water to psi can be made simple by remembering that 1 psi is roughly equivalent to 28 inches of water.