Performance Car Air Filter Test

Performance car air filters are used on almost all tuned cars. Here, we test six aftermarket cone filters to see which flows the best.

Fitting a performance air filter is usually one of the first upgrades you will make in the search for increased power. As the filter is the first part of the inlet system, the amount of air it allows to enter the engine has a direct correlation with how much horsepower the engine can potentially produce. Fitting a less restrictive air filter will allow more air in, therefore giving potential for increased power.

An air filter’s primary function is to prevent dirt and debris from getting into the inlet system and causing any damage. In terms of restriction, running no air filter is always going to be the least restrictive option, but this will allow damaging dirt and debris in, too, significantly reducing the engine’s life.

For this reason, a good performance air filter needs to find that perfect compromise of balancing filtration against airflow. One thing is certain, though – not all air filters are the same, so we decided to compare a few.


The restriction test we came up with was quite straightforward. Before we began, we tested the rig and measured the pressure losses created by the rig itself. We could then compare the data acquired when the filters were tested to get a more accurate performance figure.

To test the filters, we fitted them to the rig and increased the flow rate at measured increments. At each of these, we recorded the pressure increase and plotted these points on a graph to give a visual representation of how the restriction of the filter increases with airflow, therefore allowing a direct comparison between filters.

The best filters are the ones that had the highest flow and the least restriction, but we also took filtration into account, as while all filters give good filtration, it is widely accepted that cotton gauze filters filter dirt the best, followed by foam filters, and finally metal filters.

We really needed this test to be as scientific as possible, which meant eliminating as many variables as we could. Using J1 Automotive’s specific air filter testing rig allowed us to do just that. The rig meant we could accurately control the airflow in m3/min (cubic metres per minute) and accurately read a pressure increase just after the filter in kPa (kilopascals), to give an accurate representation of the restriction. Basically, the higher the pressure here, the more restrictive the filter is.

The tester was J1 Automotive’s Tony Cotton, who started the company in 2006 after an engineering career with Mahle developing intake systems. Since then, he’s developed many aftermarket performance intake kits and specialises in bespoke systems for clients such as BMW Mini and Aston Martin.

We asked six of the leading names in the industry to supply a cone filter they recommend for our chosen car, a Mk5 Fiesta ST. K&N, ITG, Green Cotton, Powertec, Pipercross and Jetex all agreed and sent in filters for testing. Read on to see the results…