Next up on the stock Mk7 GTI intake analysis is the turbocharger inlet pipe. The piece joins the intake accordion hose to the turbocharger compressor housing intake.
For this test the intake consists of the stock airbox minus the lower half grate, and the aFe Power dry flow air filter in place of the stock air filter.
The stock accordion hose is attached to the Turbocharger Inlet Pipe which is then attached via a coupler hose to the flowbench.
For the first test the coupler is a straight hose of equal diameter throughout.
For the second evaluation a reducer coupler is used to try and more closely approximate the transition that occurs along the air path going into the turbocharger compressor wheel inducer.
It is evident from the chart above that including the turbocharger inlet pipe along the air flow path creates a significant drop in the maximum airflow capacity; a 35% drop in CFM at the test depression.
With the reducer coupler the air flow drops another 5%, for a total reduction from the base configuration of 40%.
The percentage drop in air flow is close to the percentage change in cross sectional area through which the intake air passes along the TIP.
The diameter of the inlet and outlet are shown in the picture above. These measurements equate to an inlet area of 4.7 square inches and an outlet area of 2.8 square inches, for a change of area equal to -41%.
There is also a protrusion into the air path by a side port on the housing, which does not help to promote greater airflow through the part.
There is a substantial decrease is airflow through the pre-turbocharger intake piping with the introduction of the Turbocharger Inlet Pipe to the pathway. A drop in CFM @ 28″ of H20 of approximately 35% was measured using a straight coupler attached to the exhaust side of the TIP.
A possible future analysis could look into the dimensions of the turbocharger compressor housing inlet in order to mimic the compressor inlet for testing. That test could try to assess if the TIP restriction is an area of opportunity for performance improvement, or inconsequential so far as airflow into the turbocharger compressor is concerned.