Weak induction link.

[Kevin McDole]

Richard,

I think the answer to all of this confusion lies in the definition of a few air filter words:

Peripheral Area: the area of the filter opening. For example, a filter that has a 3" x 10" opening would have a 30" peripheral area.

Surface Area: the area of the filter material - completely unfolded. Typical ratios of Surface Area to Peripheral Area can be in ranges like 5 to 1, up to 15 to 1. - meaning that as much as 15" of Surface Area could exist for each sq in of Peripheral Area.

Active Surface Area: this is the effective surface area of the filter, as corrected for the inefficiencies of the folds and other losses. The ratio of Active Surface Area to Peripheral Surface Area can be in ranges like 4 to 1, up to 5 to 1.

The formula you are using calulates the required Active Surface Area for a given displacement and a specific RPM.

One other thing to take into account in your formula is that “A” needs to me multiplied by 1.2 for paper filters, and 1.4 for foam filters.

Bottom line, if you measure the Peripheral Area of the filter, and multiply it by 4 (just a conservative Active Surface Area ratio), you'll see there's plenty of margin.