Attention: TDR Forum Junkies Diesel Freak said:
Yes... .
But are you certain that this is 1. 5" DRAW??
For example, I can take a flow bench and as a crank up the Water Column (i. e. , go from 2" to 8"), the flow will go UP in accordance with the fan law equations.
But if the "inches of water" represents the restriction of the filter, then obviously flow goes DOWN as the restriction goes up.
So, rating your filter at a low value of WC by the latter process and creating the impression that it represents the former can result in a HUGE mistaken impression of the ACTUAL flow of the filter.
It takes 27. 6 inches of water column to represent a SINGLE PSI of pressure differential.
So, when K&N quotes a spec of 1500CFM @ 1. 5" Water (with the impression that this is the flowbench pressure drop, NOT the restriction of the filter), they are asking use to believe that a pressure difference of just 0. 05 psi will induce over 1500 CFM through their filter!
By Contrast, a Farr Ecolite airfilter from a Class 8 truck (13. 5" by 24" with a 7" outlet!) is rated 1550CFM, but at a much higher 5" of water column. Now, this level of restriction is with a PERFECTLY CLEAN filter.
A more typical ECO series air filter that is rated at 1500CFM starts out at 8" initial restriction.
Another way to break it down is this: how fast is the air moving through the filter at a given CFM?
Take the 41-1400, which is a 17"L x 7"D cylinder. Calculating the surface area give us ~374 square inches. This filter is supposedly rated at 2100CFM at 1. 5"WC. The velocity of 2100CFM through 374 Sq inches is only 9. 18mph through the media
So at 1. 5" WC (or just 0. 05psi), we'll have (according to K&N) 2100CFM flowing through the filter at 9mph. Then, when it gets to the filter outlet (assuming 5") that same 2100CFM must now accelerate to 175MPH.
Now, the K&N numbers are entirely possible, and they all seem to jive once you get past the pressure drop thing.
