Air Filter Surface Area

[cmouta]

As a numbers guy, I always like to double check age old wisdom and thought I'd share my math for fun. Occasionally I'll see a teeny BOMZ filter or something on a car and think that can't possibly be better than stock. Decided to crunch numbers on my own filter and answer my own question(cool air ducting, notwithstanding)

Stock k&n drop in specs:

Height: 4.25"
Short distance of elipse:5.06"
Long distance of elipse: 7.875"
using this calculator:
http://www.csgnetwork.com/circumellipse.html
gives me a perimeter of 20.79" so 20.79 x 4.25 = 88.36"^2


using this easy calculator for a 6" base, 4" top, 6" tall cone(K&N rE-0930)
https://www.aqua-calc.com/calculate/vol ... cated-cone
lateral A = 118.9"^2, a 34% increase in surface area!


For reference, the sierra cosworth stock intake k&n drop in is 11.125" x 10.438" panel filter with an A of 116.12"^2
That'd be a nice factory upgrade for you '89 guys(after you ditch the vam of course)

Again, just surface areas and just killing time at work before i head home

[thesameguy]

That's neat! Thanks for sharing!

I need to go measure my K&N (well, it's an AEM, but whatever). It's a cone that's 6" at some point in its diameter... I know that because 6" is my biggest hole saw, and that's the size of the hole I cut in the body to pass the filter through.

[John Brennan]

That's neat! Thanks for sharing!

I need to go measure my K&N (well, it's an AEM, but whatever). It's a cone that's 6" at some point in its diameter... I know that because 6" is my biggest hole saw, and that's the size of the hole I cut in the body to pass the filter through.

Hmmm, when I did that trick, I cut a 3.5" hole, ran a grommet around the (paint-sealed) edge, then put the 3" hose down through the top (it fit nice and snugly) to meet a 3" K&N mounted from below in front of the wheel well.

[thesameguy]

I considered something like that, but more than a few times here in Sacramento I've found myself having to drive through some pretty deep water - like a foot or so. Although I'm talking about maybe once every five years or so, and maybe once ever while I happened to be driving the XR, I just didn't want to create a situation where I'm either stuck on one side or shopping for a new engine. I keep my air filters headlight height!

[John Brennan]

Ah, so you went sideways-- I thought you were doing the old, air-filter-through-the-fender mod.

We get some pretty torrential rains/flooding here in The PHX, but I never had any issues. The filter was right up tight against the bulkhead, and my liners were in good shape.

[thesameguy]

Ah, yeah - I basically went right out where the factory inlet to the air box is... just much larger, and rounder.