How Cold Air Intakes Increase Power

All combustion engines use air and fuel to create power.
Increasing the amount of air entering the engine increases power output. There are two primary ways to increase the mass of air consumed by the engine:

  • Increase volumetric airflow (CFM)
  • Increase air density

Modifications like increasing engine displacement or installing performance camshafts can improve airflow volume. This article focuses on the second method — improving engine power by increasing air density.

 

Air Density & Temperature

Air density is directly affected by temperature and pressure (humidity also plays a minor role — humid air is less dense than dry air). To maximize performance, your intake should draw in the coldest air possible. Drawing warm air from inside the engine bay reduces air density and results in less power.

Many OEM intake systems already pull in cool ambient air from the fender well or front grille area. Aftermarket intakes should replicate this and include proper seals to block out hot engine bay air.

Cold air intake path diagram

Should You Remove the Intake Lid?

Removing the lid may reduce airflow restriction but often allows hot engine bay air to enter the system. This can reduce performance despite the increase in airflow. We only recommend lid removal in controlled environments like dyno pulls with the hood open.

Air Density & Pressure

Even if an S&B intake pulls air at the same temperature as stock, it can still offer greater air density by minimizing pressure loss. Many OEM intakes are designed with serviceability and noise reduction in mind, not airflow efficiency.

By reducing restriction — the pressure loss through the system — S&B intakes help preserve more of the incoming air’s pressure, and therefore, density.

Fun fact: 1 psi ≈ 28 inches of water. So a pressure drop of 14 in H2O is about 0.5 psi lost.

Restriction vs airflow graph

Case Study: 2017 Ford Powerstroke 6.7L

Airflow testing showed that the stock intake loses 0.45 psi of pressure at 580 CFM. At sea level (14.7 psi atmospheric pressure), air enters at 14.7 psi and exits the stock intake at 14.25 psi. In contrast, the S&B 75-5085 intake only loses 0.20 psi — exiting at 14.50 psi — a 56% reduction in pressure loss. That translates to a 1.75% increase in air density.

Powerstroke 6.7L Intake Data

In naturally aspirated engines, that 1.75% density gain equals roughly 1.75% more power. In turbocharged engines, it’s even more important: reduced intake pressure means the turbo has to work harder to achieve the same boost, resulting in hotter air out of the turbo and higher intercooler temps. In short — lower pressure at the intake means lower power, even with a turbo and intercooler.

What If the Engine is Modified?

With upgrades like a turbo, tuner, or exhaust, power gains from an S&B intake are even more dramatic. At 870 CFM, the stock intake has a pressure loss of 1.06 psi. The S&B intake only loses 0.45 psi — a difference of 0.61 psi. That’s a 4.5% increase in air density — and significantly more power potential.

Conclusion

S&B cold air intakes reduce airflow restriction and pull in cooler air. This combination increases air density — and more air density means more power.