Turbocharger Inlet Pipe Airflow Test

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.

MK7 Golf GTI Stock Turbo Inlet Pipe
MK7 Golf GTI Stock Turbo Inlet Pipe

Setup:

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.

Mk7 GTI Stock Airbox minus Grate
Mk7 GTI Stock Airbox minus Grate

The stock accordion hose is attached to the Turbocharger Inlet Pipe which is then attached via a coupler hose to the flowbench.

Flowbench test of Mk7 GTI OEM Turbocharger Inlet Pipe
Flowbench test of Mk7 GTI OEM Turbocharger Inlet Pipe

For the first test the coupler is a straight hose of equal diameter throughout.

Mk7 GTI Straight Coupler Test
Straight Coupler Test

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.

Mk7 GTI OEM Turbocharger Inlet Pipe with reducer coupler
Mk7 GTI OEM Turbocharger Inlet Pipe with reducer coupler
Reducer Coupler Test
Reducer Hose

Results:

Mk7 GTI Turbocharger Inlet Pipe Airflow Test
Mk7 GTI Turbocharger Inlet Pipe Airflow Test

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.

Mk7 GTI Turbocharger Inlet Pipe Intake and Exhaust Diameter
Mk7 GTI Turbocharger Inlet Pipe Intake and Exhaust Diameter

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%.

Mk7 GTI Turbocharger Inlet Pipe housing
Mk7 GTI Turbocharger Inlet Pipe housing

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.

Conclusion:

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.

2 thoughts on “Turbocharger Inlet Pipe Airflow Test”

  1. Will you be doing another flow test with an aftermarket TIP to compare? Looks like the car you purchased came with the APR intake, curious if you’ll flow test this (if still available to you) to compare to stock. I had an open intake and ended up going back to the stock box with grate removed and the same dry filter with the exception of a CTS TIP. Either way, awesome work!

  2. Yes, the car came with the APR TIP and that is something I plan on testing in the coming weeks.

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