Continuing the effort to improve the performance of the Mk7 GTI stock airbox I am turning my attention to the air filter.
In the previous post addressing airbox performance I utilized a stock air filter with and without the airbox grate. Removal of the grate results in a small increase in airflow and that configuration provides the starting point for the next test.
The Test Setup
Now the stock air filter will be removed and replaced by an aftermarket product.
The particular air filter that I chose to use for this test is the aFe Magnum Flow Pro Dry S Air Filter.
I specifically wanted to use a dry air filter on my GTI that could be washed for repeated use.
As for the potential performance gains from using this aFe air filter, the information provided by aFe Power states:
Up to 50% increase in Flow – 604 CFM at 1.50″ H20
I suspect somebody was not paying close attention to what they were typing when they put this information on their website because at 604 CFM a pressure drop of 1.5″ of H2O would be miniscule.
As was done with the stock air filter test the airbox was installed on the flow bench. This time the aFe air filter was installed.
The aFe Magnum Flow air filter did produce higher airflow numbers as compared with the stock air filter from my Mk7 GTI.
Airflow through the stock airbox has now been increased to 527 CFM @ 28″ of H2O. This is a little more than a 5% gain in airflow for the stock airbox versus the previous best.
How do these results compare with the advertised gains? aFe Power claims “up to” a 50% increase in airflow. This test showed nowhere close to a 50% increase, producing only a 5% increase. The 527 CFM was achieved at 28″ of H2O, which is quite a bit more pressure drop as compared to the 1.5″ of pressure drop aFe claims at 604 CFM. My suspicion is that the 1.5 number aFe is reporting is in fact PSI. If the readings I made were mathematically scaled up to 40″ of H20, which is approximately 1.5 psi, the CFM would be approximately 630, much closer to the 604 that aFe is claiming.
The aFe Magnum Flow dry air filter does provide a 5% gain in airflow through the Mk7 GTI stock airbox as compared with the stock paper air filter that my GTI is equipped with.
In a future post I’ll be looking into how the channel at the top of the grill affects air intake of the stock setup.