Dougl, Miami, and RU-2780


Jun 23, 2006
I have searched a bunch of posts, looking for the CFM of the RU-2780.

Dougl had talked to a K&N rep and stated the CFM was 191. Miami Dave said the CFM was about 145.

I called K&N and got quoted a number much higher than Dougl's number, a number that I think is far from correct. Anybody know the CFM for one of those little bastards?

Tall Tx Guy
Link Removed

Sounds pretty good to me....

Here are flow rates for various K&N filters I got from Leon Collins at K&N. The values are in cfm @ 1.5" water.

RU-2780 191 x 3 = 573
RU-1700 263 x 3 = 789
RC-1250 207 x 3 = 621

TB-2204 (under seat) = 680
Had an interesting convo with a sharp gal at K&N. She told me that the height of the RU-2780 is listed as 2.75". She also told me that if I want a true height, I need to measure the actual red part of the filter, not the red filter part and the black casing on the top and bottom. So I went and measured and determined that the actual height of the red filter part is 2.25". Using 2.25" as the height, she got a surface area of 146.

Dougl had called a while back and was told the surface area was 191. If you replaced the 2.75" length in that equation with 2.25", then the surface area is not 191 but 156.

Does the 2.25" thing sound reasonable ya all? If so, that would explain how Miami Dave got about 145.
I called them back. They base their CFM on flat surface area.

Pig9r, I'm thinking the surface area with pleats involved would actually be less than the flat surface area just because the air cannot flow through the folded "ridge" of the filter...correct?
That's debatable but keep in mind there still are each slope which contain more surface area than if it was flat. Think of flattening a triangle.

Either way I would say just a single 2780 is going to be restrictive. You might want to check your local auto parts stores and see if they had something bigger in stock that has the same diameter as your intake. If they have something in their warehouse they can get it to you in the same day.
Right on's restrictive and that's the bottom line. LoL

I will take you up on your advice. I've ordered the RU-1770. Should be here tomorrow.