A concern with using open-style intakes is that they suck in hot engine compartment air raising the intake air temperature.
A popular open intake is made by CTS and is the filter-on-a-stick design with a thin partition for separating the air filter from the engine compartment.
The CTS intake was installed on my GTI for a while and I recorded pre-turbo air temperature while it was installed.
This reading is made by a temperature probe that is installed through the turbo inlet elbow.
The GTI is equipped with a Shuenk IS38+ turbocharger and was operated in 3rd gear while conducting a few full throttle pulls.
The temperature of the air exiting the intake and entering the turbo inlet elbow was recorded and is shown on the chart below by the green “Turbo_In” line.
During the three pulls the air temperature entering the turbocharger varied from approximately 10 degrees Fahrenheit above the ambient air temperature to 15 degF above ambient.
For comparison, the stock airbox, which is a closed intake system, has also been measured.
Results with the stock airbox are shown in the next chart.
Turbo inlet air temperature ranges from approximately 6 degF over ambient to 8 degF over ambient.
The CTS open intake was tested to evaluate the pre-turbocharger air temperature. During full-throttle pulls the air temperature ranged from 10-15 degF above the ambient air temperature.
The stock GTI airbox was compared to the CTS open intake and showed pre-turbo temperatures of 6-8 degF over ambient.
The closed stock airbox provides a small improvement in pre-turbo air temperature compared to the open CTS intake.