ARM S58 Intake IAT Testing

INTRODUCTION

With Intake Air Temperatures (IATs) playing such a critical role in power and performance, it's important to ensure that the upgrades you install on your vehicle aren't raising your IATs.  With the ARM S58 Intake air filters located under the hood, it raises the question, "Does this design increase IAT's and impact performance negatively?"

THE OEM S58 INTAKE

The OEM intake system on the BMW S58 engine is a dual-filter, sealed airbox design that draws air from the front grille ducts. This setup has a geometry that can be restrictive and limit airflow volume, which can hold back power especially as you raise the boost levels. The OEM design prioritizes emissions and sound control over maximum airflow, making it a great upgrade point if you're looking for improved throttle response, turbo spool, and overall power output.

ARM  S58 INTAKE

The ARM S58 Intake relocates both filters to the passenger side (in LHD vehicles), significantly shortening the intake length for both turbochargers. This reduces the distance the air needs to travel to the turbo, enhancing throttle response, minimizing turbo lag, and reducing any change in temperature from ambient heat.  The ARM S58 Intake setup uses open cone filters with an inverted conical design for maximum filter surface area. But do open filters in the engine bay increase IAT's?  

IAT TESTING RESULTS

All of these runs were performed within 90 minutes of testing, including the time to swap the intake systems out.  The vehicle we tested on was a G82 M4 Competition with an E30 Map.  The ambient air temperature during these runs was 79 degrees Fahrenheit.  

During full-throttle pulls, we tested intake air temperature (IAT) performance by starting the car in 3rd gear and accelerating through 6th gear. In testing of both intakes, the runs ended at the same speed, 144mph.  The OEM intake began the run at 111°F and finished at 121°F, resulting in a 10-degree increase. In comparison, the ARM S58 Intake started at a lower 104°F and ended at 113°F, showing a slightly smaller increase of 9 degrees.

While both systems experienced similar temperature increases, the ARM S58 Intake maintained a 7-degree advantage in starting IAT. This difference may be attributed to the ARM S58 Intake reducing the distance and time it takes for the fresh air to reach the turbos.  Additionally, the ARM S58 Intake filters placement is directly in line with the passenger side OEM snorkel, which delivers fresh, cool air from the front of the vehicle. 

In contrast, the longer plastic runners in the OEM system are more susceptible to heat soak, which can raise air temperatures as it travels from the front of the vehicle to the turbochargers.  While the OEM intake system is a closed system, the longer runners may negate this benefit.  

It's worth noting that despite the 7–8°F difference in IAT, the wastegate duty cycle (WGDC) remained virtually identical between the two setups. This indicates that the turbos were not required to work any harder to maintain boost pressure, even with the higher intake temperatures.  

Idle testing revealed that the ARM S58 Intake maintained an IAT of 107°F, compared to 110°F with the OEM intake, a 3°F reduction. While subtle, this improvement highlights the ARM Intake's ability to better manage heat soak even when airflow is minimal, helping reduce heat buildup during extended idle periods.

Low-speed IAT testing was conducted in typical traffic conditions with speeds not exceeding 50mph. The OEM intake maintained a consistent intake air temperature, peaking at 107°F and ranging narrowly between 106–107°F. In contrast, the ARM S58 Intake showed greater fluctuation, with a peak IAT of 110°F and a low of 103°F. Despite the wider range, the ARM S58 Intake system’s average IAT closely matched that of the OEM intake, indicating comparable thermal performance under everyday driving conditions.

CONCLUSION