Thread: How Much/How big? Air cleaners.

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How big(dia x height) Does one need for good/full flow. Is taller better than dia, round vs oval, Paper vs washable?

AND.
Do any of these advertised "filter adds-ons" really work? I.E. Filter tops, Stub stacks, or others that say they add HP or is it just a bunch of BS?

Replace your paper filter with a K&N filter and you will get a lot more air.

According to K&N, the motor needs 1 square inch of filter area for each 6 CFM of air into the motor. This is ACTUAL filter area and does not include the glue around the perimeter or other protuberances that might get in the way of the ACTUAL filtering medium.

If a 350 Chevy with short cam, short intake, small carb and cast iron exhaust manifolds passes 486 CFM @ 6000 RPM's @ 80% efficiency, then you would divide 486 by 6 and find that you would want 81 square inches of ACTUAL filter area. Some 14 x 2 filters that I have seen have only about 1 3/4 inches (or less) of ACTUAL filtering medium. If you multiply 14 times 3.14159 times 1.75, you find that such a filter has an ACTUAL filtering area of 77 square inches. So, theoretically, a 14 x 2 filter will not even feed a crummy little 350 Chevy making 80% efficiency. What to do? Glue two or more filter elements on top of each other and use a longer stud. You guys with a 100% 383 will definitely need a two-stacker.

What's that you say Bunkie???? No room under the hood???? No such thing, Dude. Fire up the Sawzall and MAKE room.

I don't even say anything any more to the ricers who show up at Firebird. Some time ago, one of them laid down some long green for a Fosdick intake air system that terminated with a K&N filter. Now, this fellow terminated the filter right behind the radiator core, the worst possible place to take in intake air on the entire car. (200+ degrees F.). Well, since then, every ricer who shows up has the same idiot arrangement. It's a case of monkey see, monkey do, without ever thinking through the consequences (the car slows down).

Wow Richard, you never cease to amaze me with your technical knowledge. One of the reasons I love this site,if one asks a question one receives an in-depth answer.
I have stainless stacks 6" high with only a fine gauze to stop foreign objects getting into the carbs. It looks good and sounds good but really does it improve performance or just cutting the live of the motor down with it breathing all the road dust etc.???

Originally Posted by techinspector1

The motor needs 1 square inch of filter area for each 6 CFM of air into the motor.

Please explain where you got this number. Does it not change with each manufacture on the flow rate of the paper they each use, the number of folds (length of element) K&N? K&N copies.
Aren't they all different CFM's
Using your 1 3/4x14xpi. wouldn't that "ACTUAL filtering area of 77 square inches" be off by about 2-3 times, depending on the paper length. (folds)
When you put a residence (airfilter) in any flow, you don't go by the opening, you go by surface area residence per inch for CFM.

Pat

Originally Posted by HemiTCoupe

Please explain where you got this number.

Amended my post to say "according to K&N"....

Originally Posted by HemiTCoupe

Does it not change with each manufacture on the flow rate of the paper they each use, the number of folds (length of element) K&N? K&N copies. Aren't they all different CFM's

Probably, but we have to start somewhere. If you have a better reply to the OP's question, then please post it.

OK lets see if I got this right.

14 X 3.14159 X 3.75(4in tall filter)= 164.93 of suface area.

Great post good info for all!
i just ordered my new Billet specialties oval air cleaner and upgraded it to a 4" oval should pull some great air!
Lets see some air cleaners! could be a fun thread with some photos aswel lol


By profleetline at 2010-10-28

This is my 383 which has a Billet Specialties air cleaner with a 3 inch K&N filter.

Just my two cents, cheap does the trick, fits my style.

Looks to me like Pro fleetline, rumrumm and 406Rich had it figured out before the question came up. Nice work fellows!

tech i purchased a street scoop for a single carb for my engine. It has a small filter that fits in it. i also had to remove some of my shroud to fit the bigger fan blades. is this enough to keep my engine cool?

Originally Posted by jyardgirl

tech i purchased a street scoop for a single carb for my engine. It has a small filter that fits in it. i also had to remove some of my shroud to fit the bigger fan blades. is this enough to keep my engine cool?

The filter shouldn't have anything to do with cooling the motor. It has to do with breathing and supplying enough air to make good power.

As far as the fan shroud, could you post a picture of what you did?

will tomorrow tech. thanks. what i meant to ask is the scoop filter enough for my engine to breathe and the shroud modification enough for my engine to cool.

A filter has to cause enough obstruction to particles in the air (dust, dirt...) but also needs to let air through.
The aperture size is very secondary here (because the aperture size of the carb is the real restriction to airflow at only a couple of square inches), it's the flow capability.
An air filter works like this: Its a fine mesh with very small holes in it. The smaller the holes, the better the filtering is going to be (i.e. less dirt in the motor = longer life). But on the other hand smaller holes will only let less air through. So to get a good flow of clean air you need very many very small holes. Easiest way to get more holes is to enlarge the area of the mesh. This is done by folding the filter material, thus fitting more mesh into the same aperture size.
Apart from the brand name K&N filters cost more because they use better filtering material (the material itself has more and smaller holes).

Much more important than the aperture size is to use a clean filter. Dirt clogs up open style filters quite quickly, because it stays in the small holes, as no air coming the other way (out of the carb) will blow it back out of the holes. Even unwashable filters can be cleaned quite well with compressed air blowing outwards from inside the filter (take it off the engine first or you'll blow dirt into it).

A typical filter will have a total area of 3 or 4 times the aperture size. Most open style filters suffice for street applications.

Note on scoops: The filter in scoops are mostly smaller all round, but have bigger foldes in them, so the mesh area isn't a lot smaller (if at all). After all, they are designed for scoops...

For tech's 6 square inch rule: Measure the length of one fold, multiply it by the height of the filter and by the number of folds (just count 'em).