A question was asked if the small chamber at the back part of the lower half of the stock airbox has an effect on the airflow through the airbox.
This was not something that I’ve tested so when an opportunity arose I ran an experiment to see if a difference in airflow would result from blocking off the airbox chamber.
The stock airbox was assembled with an air filter and accordion hose and attached to the flow bench. The bench was operated at 28″ of H2O and the airflow through the airbox was recorded.
The airbox was then opened and a piece of foam was inserted into the chamber at the back of the airbox to block it off. The airbox was re-assembled and attached to the flow bench for a repeat of the test.
There was no measurable difference in airflow between the two airbox configurations within the margin of error of +/- 2 CFM.
Airflow measurement made with a flow bench did not provide any evidence to indicate that the chamber opening at the back of the stock GTI airbox has an effect on airflow through the airbox.