There are some tests out there where they do a more scientific test... I'll look for the book mark. They used MEASURED particulate which is all a known size and suck that through the filters while measuring the difference in air pressure outside the filter vs inside (using a device known as a differential manometer) Amsoil and AEM were the top dogs, IIRC. I don't think Apex'i was included. IMO Apex'i, AEM and Amsoil are all excellent choices... I lean toward AEM just because I switched to those before I found out about Amsoil's offerings. I switched from Apex'i when my old one got damaged and I found I could get the AEM for half as much.
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