Post

[GreenCobra]

I have a question about air filters. The foam one in my Stellings and Hellings filter housing has given up the ghost. Dirty, crumbly. So I am looking around for a replacement and checked in with K & N.

To fit in the S & H housing and under the hood I need a round filter that is 8" OD and less than 2" tall. The closest match was a filter for a Mazda, 8" X 1.75". Part # E-9181.

Mazda - pretty small engine..would a Mazda filter flow enough air for a 427? So I email K & N tech and ask about the flow charateristics of the Mazda filter.

Very nice response that, in summary, said that the K & N cotton gauze filters flow 6 cfm per square inch and that the Mazda filter is rated at 263.89 CFM.(don't ya love that - out to the hundreth of a CFM!!) The tech consultant said that I could calculate my engine's CFM needs using the following formula:

Cubic Inches X Max RPM / 3456 = CFM of engine.

For a 427 that come out to be about 800 CFM. So looks like the Mazda filter would choke the engine.

So I did a little research on foam filters. They must have much higher flow rates than cotton gauze, right? Otherwise my engine would be suffocating. Well, apparently not. It depends on the foam density but high performance foam filters actually flow a little less efficiently than the K & N.

I went to the Cobra Country classified listing and saw that a lot of the engines are equiped with the S & H filter housing and a filter that looks like a K & N, about the same size as the Mazda filter.

So how does that work? My engine sure doesn't feel starved for air and I am sure those ones in the classifides don't either. Maybe the K & N standard of 6 CFM per square inch of filter surface is too conservative?

Any thoughts/suggestions? Thanks, GreenCobra