I am currently using a K&N air filter that is 12.5" OD, 11.0" ID, and 2.75" tall. I would like to gain some hood clearance and I have found a filter that is the same OD/ID but it is 2.12" tall. Is there a way of checking to see what cfm or hp rating an air filter size might have?
I just want to see if down sizing the air filter won't hurt my 340 setup.

Thanks

are you going to try to use the stock top? i lost 2 full tenths running a new paper air filter in the stock housing with the lid tighten down and sealed. Most F.A.S.T. guys i see with that cleaner run a filter thats maybe a 1/4 to 1/2 " taller which makes the lid have a gap allowing a lot more air into the engine than the two small oval cutouts.

I do not run the stock lid for that same reason. I made a round plate lid which allows in more air. I would run it the same as above but the lid would be 5/8" lower with the other filter that I am looking at.
Thanks for the reply.

How about one of those pleated top covers? Breathes through the sides and the top.

John,
Can you show me a picture of the pleated top?

Ademon,
How tall is your current air filter?

Thanks for the replies.

The K&N websight showed the same stock size air filter for a 340,383, and 440. Now I am guessing that if a 2.75" tall unit is good for a 440, and I am currently using one on my 340, then I would not be missing much by going down to a 2.12" tall unit.
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I found this on the K&N Websight:

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= CID x RPM divide by 20,839 = effective filter ara

My combo: 340 x 5800 divide by 20,839 = 94.6 sq. inches

Current Air Filter: 12.5"od filter x 3.1416 x 2.75 (-.75)= 107.2 area

2.12" tall: 12.5"od filter x 3.1416 x 2.12 (-.75)= 82.5 area
Minimal Air Filter: 12.5" od filter x 3.1416 x 2.50 (-.75)= 97.4 area

I can only go down to a 2.50" tall unit which may not be worth it. I will next measure the inside of my stock 340 air cleaner housing to see what the max diameter filter that can fit and see if a 2.25" (or so) filter would be enough flow.

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I found two sizes that might fit depending on the ID of the 340 housing:
#E-3740: 14.0" dia x 2.31" tall [@ 100.8]
#E-1580: 13.2" dia x 2.5" tall [@103.3]

Thanks John. That is a cool looking piece.

Update:

I searched thru a couple different filter manufacturers and I could not find a paper filter in the size range that I need to get the amount of volume that I need (96 sq. inches minimum) and to lower the filter lid. So I opted for the K&N filter #E-3740 (100 sq. inches). This filter has a 14.0" outside diameter and a 12" inside diameter and it is only 2.31" tall. My existing K&N filter is 2.75" tall (107 sq. inches) and this new filter will give me an additional .44" of hood clearance and I can keep my original 340 filter assembly (minus the original top lid like shown above).
My exiting top lid is 13" in diameter which should be enough to keep the new filter in place. I might have to modify the inside of the 340 air cleaner pan slightly by bending down the air deflectors, but that is a minor change that won't be very noticeable.

Note:
After watching the other filter thread, I was hoping to go with the paper filter this time but the sizes available would not allow that change.

Thank you for the replies.

I got the 14" x 2.31" tall filter and my 13" diameter lid worked fine. I gained .4" of hood clearance and was able to keep running my original hood cleaner base. I did have to remove the original air dams in the base, but I would rather have the hood clearance. I don't have any pictures but it looks just like my first picture (without the dams shown) and my lid is now just above the height of the air cleaner sides.
This was done due to me adding the rpm intake, two Cometic heat insulators, and a carb heat shield. This stackup was too much for my rallye hood.

you removed the air dams on the air cleaner base

Yes. Since I am using a 14" filter instead of the original 12.5", I needed to remove them. Since I am not using the oval openings in the base as the only air intake, I do not need them. The 14" filter covers where the air dams were and since the ID of the base is 17", this leaves 1-1/2" all around the inside for air.

I added a poor quality phone picture to show the new filter. Notice the height difference from the first picture.