Wednesday, February 8, 2012

Clean Air Filters and Performance

Best Air Filters Review: Air Filter Facts
Air Filter Facts Part 8: Clean air filters and performance- more evidence 

In our last post we reviewed Diesel Power Magazine air filter tests, which conclude that swapping air filters alone does not impact performance (for clean filters). Can we confirm this test's results across other tests? We were not able to find other credible tests.  But we did find information provided within the industry which corroborates, in our opinion, Diesel Power Magazine's results:
  • Castrol, of motor oil fame, also sells air filters. Its expert advice section, in a Q&A page ("More Air, More Horsepower) states: "When it comes to modern engines with electronic ignition and fuel control, an air filter upgrade in conjunction with a cold air intake can yield horsepower gains." This statement clearly implies that an air filter upgrade alone, without a cold air intake, is unlikely to yield horsepower gains.
  •  Comptech, a manufacturer of performance parts for Japanese cars, writes to one of its customers: "Your ECU [Engine Control Unit] shouldn't be affected by changing the filter only." This implies, of course, that a drop-in air filter change will not affect performance. 
  • Perrin Performance, a manufacturer of performance high flow filters, writes in its Filters Q&A: "We sell our filters by saying all filters when new flow about the same [...] In an example of an OEM filter being replaced with a PERRIN foam filter (on an STI), we see about a 3 wheel Horse Power gain.  This is not much at all and not something you can generally notice." In fact, we are no even sure that their measurement (certainly from a dyno) would be statistically significant, as dyno experiments are typically not accurate within 3 hp. What is significant is that the manufacturer recognizes the gain as minor, if any. 
  • While many filter manufacturers claim that their filter will improve performance, none actually publish any third party tests proving such increase in performance. We find it unlikely that such would be the case if an improvement in performance could actually be documented.
While we find none of these facts sufficient by themselves, we consider that, together, along with Diesel Power Magazine's tests, they prove conclusively that no notable gain of performance can be obtained from swapping air filters alone. Our conclusion is that changing drop-in air filters does not affect vehicle performance in a measurable way.

  • Swapping drop-in air filters alone does not improve vehicle performance for a clean filter

But could this conclusion be different when applied to the same filters when dirty? Next we discuss difference in performance between drop-in air filters when dirty... So come back soon!

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