Several aftermarket parts manufacturers sell engine air intake filters that they claim provide better airflow and consequently increase a car’s power and acceleration.
Some of these companies have many loyal customers who swear they have benefited, particularly in terms of performance, from using these high-flow filters.
These filters are often made of cotton or nanofibers, and some are washable and can be cleaned and lubricated with a special oil then reused, with at least one brand guaranteeing they will last a million miles. Others can be cleaned with an air hose and reused. Many are designed to directly replace the original paper air filters in cars provided by automakers; other reusable designs are included in a freer-flowing air intake system that supplies more fresh air to the engine.
On the surface, these claims about intake filters make sense. Engines are like athletes, because the better they can breathe, the faster they can go.
However, independent tests have shown that these replacement filters may provide little to no performance benefits, and some types of reusable filtration units allow more dirt into the engine. This dirt will enter the engine oil and the abrasive effects can damage internal engine parts. Additionally, some users claim that the oil sprayed on some of these types of filters also enters engine air intake systems.
The EPA has not tested oil bath filters or other free-flowing air filters, but it has conducted tests comparing clogged conventional air filters with new ones. The EPA found no significant loss in fuel economy from a clogged air filter, but found in a test of gasoline vehicles that acceleration improved with a clean air filter.
While this seems to lend some credibility to claims that a reusable, freer-flowing air filter can improve acceleration in a car or truck, the extent of the performance gain depends on the specific vehicle. Furthermore, these high-performance filters cost more than conventional filters, and although they may last much longer, they require periodic cleaning and maintenance instead of periodic replacement. High-flow filters and intake systems typically muffle induction sounds less than classic paper filters, which can create the impression of better performance – or simply a desired sound – that makes the entry price worthwhile for some drivers.