Monday, March 14, 2011

Air Filters: Can They Improve Air Flow?

Best Air Filters Review: Air Filter Facts
Air Filter Facts Part 3: Can air filters improve air flow?

In the next few posts, we will investigate if you can improve automotive mileage and performance (i.e. acceleration and torque) by swapping drop-in air filters that have higher air flow. We already know that air flow through an air filter does not impact mileage in modern cars. Because so much opinion on air filters is based on assumptions rather than facts, we should ask - can we measure meaningful differences in air flow between air filters?

Air flow differences across air filters  is a federal government site focused on - guess what - fuel economy.  Under their aegis, the famed Oak Ridge National Laboratory published, in February 2009, a research report investigating the effect of air filter condition (i.e. air flow restriction) on fuel economy. The researchers experimented with both modern fuel-injected engines, and with older carbureted engines. They showed conclusively that some aftermarket (high flow) filters were able to provide more air flow than OEM filters, measuring a lower pressure loss across aftermarket filters than OEM filters:

These tests were done on the vehicle itself, at wide open throttle for 10 seconds. There is a clear difference  between no filter, high flow aftermarket filters, and the OEM style filter, which experiences the highest pressure drop (meaning the least air flow, but also, probably, the best filtration). So, clearly, it is possible to increase air flow (and decrease pressure drop) by using a different drop-in filters. We will see later than the K&N filter is particularly successful at that. However, the differences, when compared to atmospheric pressures, are very small - so it is not clear if these will result in actual changes in mileage or performance. 

  • Non-stock air filters can improve air flow

How much worse does air flow get when your air filter gets dirty? Is there a measurable difference? Next we discuss the impact of dirty air filters on air flow... So come back soon!

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