Whether this helps or not, I am not sure but this is an extract out of a book **"Turbo: Real World High Performance Turbocharger Systems" by Jay K. Miller.**

"Use this formula to calculate how many square inches of K&N style filter you need. The formula is courtesy of K&N filtration.

**Square inches of filter required = (lbs boost / 14.7) + 1 x CID x Max RPM / 20,839**

For example: at 10 lbs of boost, a 3 liter engine (183 cubic inches) that's designed to create max power at 6,000 rpm will require 88.5 square inches of filter.

**(10 / 14.7) + 1 x 183 x 6,000 / 20839 = 88.53 square inches.**

The filters are pleated to allow more surface area within a given diameter for packaging purposes. Now, to help you choose a filter, determine the diameter that will fit your installation, and then use the following formula to determine the filter length (or height, depending on orientation). (Note that this calculation is for round filters. For cone shaped filters, simply estimate the average diameter, which should be about half of the larger diameter plus the smaller diameter.)

**Filter height = (inches of filter / Filter Dia. x 3.14) + 0.75**

Consequently, in the above example, if you had room for a 12 inch diameter filter it would require a filter height of about 3 inches.

**(88.5 / 12 x 3.14) + 0.75 = 3.1 inches**

If this seems large to you, then you now understand the value of a properly sized air filter assembly and the value of knowing how to design your own turbo system.

Once you have captured the air, it's time to route it to the compressor inlet. If you have a few feet to navigate, keep your tubing as large as room will allow. This reduces tubing line loss. Unfortunately, air likes to slow down before it is redirected, which means you'll want a smooth track with as few bends as possible."

I used this calculation to determine whether an AFE DCI was large enough for my requirements and it came out too small so I designed my own dual cone with larger cone filters.