Mk7 GTI Modified Stock Airbox Flow Test

Mk7 GTI Stock Airbox Modification Testing

Background:

A question was asked about modifying the stock airbox by adding holes to potentially increase airflow. This post describes making additional openings to the stock GTI airbox and the effect on airflow through the intake.

Modifications:

To begin, a baseline measurement was made using the stock airbox that has the grate removed, an aFe dry filter in place of the stock air filter, and the plastic accordion hose replaced by a silicone hose.

An MST Performance turbo inlet elbow is used to attach the intake to a simulated IS20/38 housing adapter that is then connected to the flow bench, simulating the GTI intake setup to the turbocharger.

The baseline setup flows 377 CFM @ 28″ of H2O

Mk7 GTI Stock Airbox Flow Test
Mk7 GTI Stock Airbox Flow Test

The turbo inlet elbow is removed and the remainder of the intake is attached to the flow bench, which will be the configuration used during the airbox modification.

This configuration flows 556 CFM @ 20″ of H2O

Mk7 GTI Stock Airbox Direct to Bench Flow Test
Mk7 GTI Stock Airbox Direct to Bench Flow Test

The first alteration to the stock airbox is the addition of three holes to the side of the airbox:

Mk7 GTI Modified Stock Airbox - 3 Holes
Mk7 GTI Modified Stock Airbox – 3 Holes

The airflow reading increases to 560 CFM @ 20″ of H2O.

Next, the three holes are combined into a single slot.

Mk7 GTI Modified Stock Airbox - 1 Slot
Mk7 GTI Modified Stock Airbox – 1 Slot

The slotted opening flows 566 CFM @ 20″ of H2O.

An additional slot is made adjacent to the first.

Mk7 GTI Modified Stock Airbox - 2 Slots
Mk7 GTI Modified Stock Airbox – 2 Slots

The airflow measurement is now 564 CFM @ 20″ of H2O.

Note: +/- 2CFM is an approximate margin of error for the airflow reading. The addition of the second slot did not result in a measurable change to the airflow.

To assess if an additional opening might produce an increase in airflow a third slot is made, approximately two-thirds of the height of the first two slots.

Mk7 GTI Modified Stock Airbox - 3 Slots
Mk7 GTI Modified Stock Airbox – 3 Slots

Airflow with the three slots measured 567 CFM @ 20″ of H2O.

Progression of airflow through the airbox as modifications are made is shown on the comparison chart:

Mk7 Airbox Modifications Airflow
Mk7 Airbox Modifications Airflow

The modified airbox is then reattached to the flow bench using the turbo inlet elbow and turbo cover adapter.

Mk7 GTI Modified Stock Airbox Flow Test
Mk7 GTI Modified Stock Airbox Flow Test

The airflow through the modified stock airbox is 384 CFM @ 28″ of H2O.

Comparison of the before and after with the turbo inlet elbow:

Mk7 GTI Airbox Airflow Testing
Mk7 GTI Airbox Airflow Testing

Conclusion:

Adding openings to the Mk7 airbox increases airflow through the intake slightly.

With a turbo inlet elbow attached the airflow increased from 377 to 383 CFM @ 28″ of H2O.

Without the turbo inlet elbow the airflow increased from 556 to 567 CFM @ 20″ of H2O.

Next, determining the effect that opening the side of the airbox has on air temperature through the airbox will be evaluated.

3 thoughts on “Mk7 GTI Stock Airbox Modification Testing”

  1. Very cool!
    Takes me back to my mk3 Jetta days and modding the stock airbox. Quickest improvement was from pulling the box’s inlet “horn”.

    1. I recorded data using both and put together some preliminary charts. Differences were hard to detect. I lost interest in continuing when it became apparent I would have to better control the conditions during data collection.

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