Air Filter Size?

[sailsmen]

Per K&N*
"That brings us to size.

Use the formula below to compute the minimum size filter required for your particular application. The usable portion of the filter is called the EFFECTIVE FILTERING AREA which is determined by multiplying the diameter of the filter times Pi (3.1416) times the height of the air filter in inches, then subtracting
.75-inch. We subtract .75-inch to compensate for the rubber seals on each end of the element and the filter material near them since very little air flows through this area.


A = effective filtering area
CID = cubic inch displacement
RPM = revolutions per minute at maximum power

Example: A 281 CID Ford engine with a horsepower peak at 6,500 rpm.

281CI X 6,500RPM / 20,839 = 87.65


If you are sizing a panel filter, multiply the width of the filter area (not the rubber seal) times its length."

The panel filter would need to be 9.4"X9.4".

The filter I have is 127.25" in Effective Filtering Area.

*Note: changed to reflect MM application.

[gdmjoe]

sailsmen ... 281CI X 6,500RPM / 20,839 = 87.65
What is the 20,839 ?

Inquiring minds want to know.

More air filter math' ...
281 CI - engine CubicInch(es)
35.128 CI - cylinder CubicInch(es)
.020328 CF - cylinder CubicFeet
101.64 CFM - cylinder CubicFeetperMinute @ 5000 RPM
450 CFM - FA-1805 *Mercury Marauder air filter CubicFeetperMinute.
320 CFM - FA-1668 *Crown Victoria air filter CubicFeetperMinute

Ignoring vaporized gasoline also in the cylinder and doubling the cylinder CFM ( figuring that intake valve is open on one and 2 are staged ) ... 304.92 CFM.

Even the Motorcraft air filter for the Crown Victoria is MORE than adequite to provide the necessary air @ 5000 RPM.

Advantages over K&N: better filtration.
no oil contamination of the MAF ( nor possibility thereof ).

[J.bo]

So the paper Motorcraft filter is better at filtering air over the K&N panel filter or are you saying the paper flows more cfm than oil soaked filter? I just recently switched back to the stock filter box with a K&N filter.

[sailsmen]

The formula is per K&N. I assume for a normal service interval. I assume your flow rate is for a new filter.

What is the basis that the paper filters better?

Oil contamination is no more and issue than the paper element breaking up and damaging the MAF.

[J.bo]

Oil contamination is from over use of oil and oiling the wrong side. I only oil the side that is opposite of the maf. Then I let it sit overnight on newspaper to soak up any possible over oiling. With this method I have never had a oil contaminated maf.

[sailsmen]

Oil contamination is from over use of oil and oiling the wrong side. I only oil the side that is opposite of the maf. Then I let it sit overnight on newspaper to soak up any possible over oiling. With this method I have never had a oil contaminated maf.

I thought you were supposed to spray the inside of the intake and the maf to get max air filtration?

[musclemerc]

What is the 20,839 ?

Inquiring minds want to know.

More air filter math' ...

281 CI - engine CubicInch(es)
35.128 CI - cylinder CubicInch(es)
.020328 CF - cylinder CubicFeet
101.64 CFM - cylinder CubicFeetperMinute @ 5000 RPM
450 CFM - FA-1805 *Mercury Marauder air filter CubicFeetperMinute.
320 CFM - FA-1668 *Crown Victoria air filter CubicFeetperMinute

Ignoring vaporized gasoline also in the cylinder and doubling the cylinder CFM ( figuring that intake valve is open on one and 2 are staged ) ... 304.92 CFM.

Even the Motorcraft air filter for the Crown Victoria is MORE than adequite to provide the necessary air @ 5000 RPM.


Advantages over K&N:

better filtration.
no oil contamination of the MAF ( nor possibility thereof ).




Agreed, but I think I know the point Sailsmen is trying to make.
He sent me this info in a PM and I havent gotten around to replying.

The panel filter surface 9.4" X 9.4" is what he's getting at.
Maybe to imply my new CAI has an inadequate filter surface?

Here is another opinion that is not a copy paste from some manufacturers website.
There are alot of variables that are left to the unknown even with their calculation. What about airbox design? Materal used (metal/plastic)?
How big of an air inlet opening on the box for this mandatory 9.4" X 9.4" panel filter? How far should it live from the MAF? How long of a zip tube to feed the 281CI? I can keep going....

Even with K&Ns formula it leaves you where? I've seen sub woofer companies offer more information on specs for a sub enclosure (exact dimensions, height, width, port size, amp type, etc) than this.

[CBT]

I thought you were supposed to spray the inside of the intake and the maf to get max air filtration?

With the K&N air filter oil?! You have an 11 second car and you seriously thought you spray that crap INSIDE the intake and MAF? I don't believe it, you must be pranking him.

[LANDY]

With the K7N air filter oil?! You have an 11 second car and you seriously thought you spray that crap INSIDE the intake and MAF? I don't believe it, you must be pranking him. I know it seem like a sarcastic question

[sailsmen]

I am not sure the filter I have is big enough.
The "K&N formula" says 87.65" for N/A. I am S/C and about double N/A in power.

My filter area is 127.25". Is that sufficient for a 281CI making ~600CHP?

In theory the air must flow through the filter. You can have the largest structure in the World behind the filter and it still has to flow thru the filter. Assuming the same medium the larger filter will flow more air.

You would think there would be a guide. I think the Factory Filtration Area is a place to start, the o/s dimensions are 11.25"X7.56" resulting in an Effective Filter Area of 84.3.

( I was joking about the oiling. Any product that is missused or abused will generally not work as intended. Don't use gas powered lawn mowers, if you poor the gasoline on the hot exhaust it may catch fire!)

[J.bo]

I thought you were supposed to spray the inside of the intake and the maf to get max air filtration?

You trying to be funny and not! I was just expressing the proper usage of the oil and application. Believe it or not someone may not have known and is oiling both sides of the filter.

[sailsmen]

I wasn't making fun of you. I was making fun of an "advantage" being contingent upon not missusing a product.

[sailsmen]

I asked both K&N and S&B what size filter for my application. If they respond I will post it.