my stock air breather filter is a 14"...the sizes available are 9,11,14" my question is is there any advantages/disadvantages to using a smaller filter or larger one

if you are not familiar with this product heres a link:
http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_92772_-1

The bigger the air filter is the more air flow you will get out of it. If you want the extreme air flow lid the 9" filter is plenty for a street motor. Smaller filters will give you more room under the hood. I would recommend the 14" filter with a crome lid because I think they look better. It will out flow a stock element by far.

There is a formula to finding out how big an air filter to use.

A=CID X RPM/20,839
RPM= Maximum power RPM

For example I have a 350 so I would take 350 x 6200RPM / 20,839=104 Square Inches.

Then to find out the height of the filter use this formula.

H= A / D X 3.14 + .75
A= Affective filtering area from 1st formula.
D= Outside diameter of filter
.75= rubber end caps of filter.

So again my example would be

104 / 14" x 3.14 + .75= 3.12

I would need a filter that measured 14 x 3.12 for optimum air flow. That's getting down to nitty gritty.

Here is a link to the formula in case I confused you...
http://www.knfilters.com/filter_facts.htm#RESULTS

a test hot rod did quite some time ago showed the differences on a zz454 crate with an eddy rpm air gap, a JET 850 carb, HEI, 1.5 inch wilson spacer, CSI electric pump, and hooker 2" 2213 headers

all K&N filters
HP/TQ
open carb: 502/534.3
carb w/ stubstack: 507/537.5
3 inch element with drop base: 505/534.5
3 inch element with drop and xtreme top: 499/532
3 inch element with drop and xtreme top, stubstack: 506/536.1
4 inch element with drop base: 506/537.9
4 inch element with drop and xtreme top: 507/539.6
4 inch element with flat base and stubstack: 509/538.4
4 inch element with flat base, stubstack, and xtreme top: 507/540.5
4.5 element K&N flow control w/ xtreme top: 508/539.8

Might check out this (http://speedtalk.com/forum/viewtopic.php?t=7285&highlight=) response on the subject by Joe Sherman.

Eric