Performance Car Air Filter Test
With all the results in and the calculator having worked overtime, we can sit back and work out what it all means. The first thing to note is just how incredibly restrictive the standard airbox setup is. The engine is effectively being strangled with the standard airbox fitted, therefore the best thing you can do to a Fiesta ST, and indeed many other cars, is get rid of it and fit a less restrictive cone filter. It is also worth noting that the price difference between a performance panel filter and the standard item is so small that it really isn’t worth keeping the standard filter at all.
As for cone filters, we’ve already established that all the cone filters are much less restrictive than the original airbox, but there was quite a big difference between the performance of the cone filters on test, too. Firstly it was a bit of a surprise to learn that the K&N was the most restrictive, especially as it is the filter of choice for many tuners, but this was most likely due to its small size rather than anything else.
The Jetex made a big impression by being the best cotton filter on test, beating both the Green Cotton and K&N items. The two foam filters both performed well, with the Pipercross marginally outperforming the ITG.
The Powertec was the only stainless-steel mesh filter on test and it clearly offers the least restriction, as you can see from the graph. There was actually a 0.55kPa difference between the Powertec and the K&N.
In terms of filtration, the standard paper item is always the best because of the stringent standards OEM products have to meet. We put this to the test after the flow tests and it had an incredible 99.75 percent efficiency, but as you will have read, it is very restrictive indeed.
In comparison to the paper filter, the two performance panel filters we tested were not as efficient as paper, with 77 percent for the ITG for example, but they would still be adequate in most conditions.
There are a few lessons that can be learnt from this test. The main one being that on most cars you should bin the standard airbox if you plan to increase the power. There also seems to be a direct link between efficiency and restriction – the less restrictive a filter is, the less efficient it is. Therefore, we can surmise that the cotton filters will have better efficiency percentages than the foam ones, but by the same token they are more restrictive in terms of airflow. Applying the same logic, we can deduce that the stainless- steel mesh filter isn’t likely to have a high efficiency percentage.
Therefore, you need to decide which medium is best for you, as there are pros and cons to each. Generally, it’s a compromise between power potential and engine protection, but if space isn’t an issue, then the larger the filter, the more even a restrictive filter medium can flow.