air filter for mini - flow test

I recently decided to try a K&N filter for the Mini over the genuine MINI air filter. It was actually a long story that resulted from my investigation starting off with my questioning the hypes of the aftermarket "cold air intake".

For now I would not bore my readers as to why I chose the K&N panel filter that is a drop-in fit in place of the stock air filter. I only proceed to make the purchase when I was convinced that it might provide better flow (less restriction) than the factory one. Today I spent some time to make a simple test fixture out of a cardboard box. I planned to use a shop vacuum to emulate the intake suction of an engine. I set up a simple water column vacuum gauge.

stock filter (left) and K&N filter (right)

It turns out the shop vacuum while can pull very high suction, the airflow CFM is too low to make visually discernible rise of the water column. I turned to plan B - using a high flow computer fan. I didn't want to turn this exercise into a production so I was just hoping the computer fan would work. I knew it would be marginal at best.

this is a 12V fan

the small hole was first created for the shop vacuum; I enlarged it for the computer fan

 I tape the fan to the opening with packing tape

on the opposite end a small hole is created for the water level gauge

my neighbor wanted to see the experiment; the slight change in the water column was only a few millimeters

I wanted to keep the fixture very simple so the air filter just rest on the rectangle cutout and seal itself

here is the K&N being tested

to make it easier to see the water level change I place the two columns side by side and added a ruler to read off the delta

here is the stock filter - reads 4.5mm

here is the K&N - reads 2.5mm

This experiment is intended to be a rough comparison. As I don't know the CFM rate the reading should be interpreted with caution. I would estimate the fan draws about what the Mini's engine at idle. At this flow rate, the K&N filter is 55% as restrictive as the stock air filter.

Originally I was thinking of using one of these cone filter but in the end I decided the panel filter is my best choice.