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# Automotive Air Filter Sizing/Flow Calculations2

## Automotive Air Filter Sizing/Flow Calculations

(OP)
Hello,

I'm trying to determine how much air flow a given air filter can handle.  Does anyone have any calculations to determine roughly what a filter can handle?  I'm using a K&N type lubricated filter.

Thanks

Denis Kefallinos
Replies continue below

### RE: Automotive Air Filter Sizing/Flow Calculations

Hot Rod or Chevy High Performance did a flow comparison of all the gauze filters a few months back, I don't remember the exact month either though, but it is out there.

### RE: Automotive Air Filter Sizing/Flow Calculations

Here are some formulas for K&N type filters. I believe these were found at the K&N website. Hope this helps.

Area = (CID * RPM) / 20839
Area = (Height - .75) * (Diameter * 3.141593)
Area = Length * Width
Height = (Area / (Diameter * 3.141593)) + .75
Diameter = (Area / (Height - 0.75)) / 3.141593
CID = (20839 * Area) / R
RPM = (20839 * Area) / CID
Width = Area / Length
Length = Area / Width

Paper Flows 57.3% of K&N
Foam Flows 42.4% of K&N

I also have a program if you are to lazy to do it on the calculator. Go to http://mywebpages.comcast.net/stevehuckisnot/freestuff.htm

### RE: Automotive Air Filter Sizing/Flow Calculations

Sorry, no dimensional data, but in general a pressure drop across the filter shouldn't cost more than 1.5" water.  This can be pushed to 3.0", but the 1.5" should be used whenever possible.  We test air cleaners on the flow bench, but you could always instrument it in the vehicle for the most accurate result.

### RE: Automotive Air Filter Sizing/Flow Calculations

Now that's a number I've been after for a while. 3 inches of water is 0.7 kPa. Worst MAP (measured at the plenum) at full throttle I've ever seen is 5 kPa, in a prototype, and 2 kPa in production.

Thanks for that.

Cheers

Greg Locock

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