I found this on Ford-Trucks.com and figured it'd be useful.
>>AIR FILTER SHOOT-OUT
Author: Pierre Lafontaine - Air Inlet Systems
(14x3" Results Chart)
(14x4" Results Chart)
The established performance brand of choice has quickly become K&N. They claim a substantial flow advantage over paper. Our results show this to be fairly accurate. The only filter to outperform the cotton gauze filters are the Nascar qualifying filters by WIX Racing. Unfortunately, these Wix glass fiber filters are very expensive and not washable. However we tested it to obtain the highest possible flow value in each category. As the results show, the K&N 14x3" and 14x4" are down only 25 cfm, flowing at 97% of the Nascar filters. Nearly even are the AIS (Air Inlet Systems) prototype versions of the same material.
We don't see the paper filters show up until about 91% of max flow. The Fram 14x3" flows a bit under 800 cfm. Interestingly, the AC Delco 14x4" (paper) flows nearly the same as a 14x3" cotton gauze. Right on its tail are the two foam filters at a hair over 90%. Now, this is where it gets interesting. Paper filters range from 91% to 69% in airflow capacity. The Moroso paper filter we paid $15.95 for did pretty good, as far as a paper filter is concerned, came in second with about 90%. Then there are the middle of the road paper filters, all pretty close, can't really choose a winner there. Wix gets to open and close the list. These last models are designed for extreme off road service with superior filtering efficiency, and not intended for normal service.
Who claims what? When K&N tests at 0.3" H2O, using a standard, cylinder head air flow conversion formula and extrapolates to 1.5", they may not be making a correct assumption. We are dealing with a restrictive medium, not a free flowing cylinder head port. They claim 50% greater flow with a K&N over paper. Our results show this claim to be quite a bit off! Most paper filters rated between 80 % and 90% of the cotton gauze types. Amsoil claims to marginally outflow K&N but this could not be shown in our test. Both Accell and Amsoil foam filters flowed about as a good as a premium paper filter, around 90%, indicating that the foam filters are getting better.
Also note the swirl coefficient. The more turbulent it is at the entry to the carb, the more venturi buffeting occurs, which can disturb atomization of the fuel. The higher the number, the greater the turbulence. This factor should be considered. It seems that the shorter filters create more. Another aspect is using a filter that is big enough for the engine power levels. The flow numbers listed are close to the established CFM requirement for engines. It is easy to see that some combinations should be avoided. A slow speed engine may not suffer so much with a restrictive filter but it could cost as much as 20 hp on a high RPM race motor. The average 300-hp street motor will stand to gain around 10 hp from the best to the worst.
In conclusion, the cotton gauze filters are the best flowing filters when new. Being reusable, and with proper maintenance, it may be the last filter your hot rod needs. Paper, if you are willing to replace it often, will flow very close to cotton gauze. The foam filters are also reusable and probably more resistant to washing damage. Foam will The foam is down 10% on airflow capacity, which puts it about even with a quality paper filter. Priced at about 2/3 for the same size in cotton gauze, it's a viable alternative. At and average of $8 for a paper filter, $35 for a foam, and $50 for a cotton filter, we are talking about potentially a 10-hp difference on a V8. From the chart, you can tell if the filter you are using is big enough. With this information on hand, you are better equipped to decide which filter is best for you. F/M
Air Filter Flow Test
14" x 3" Round Flow # @ 5" H2O % Flow Rating Swirl
Brand Part # Size Material
Wix 46945R 14x3 Glass 860 CFM 100% 119
K&N E-1650 14x3 Cotton 835 CFM 97.1% 126
AIS Cotton AF3C 14x3 Cotton 830 CFM 96.5% 121
AIS Cotton AF3C-2 14x3 Cotton/Synt 830 CFM 96.5% 130
FRAM FRM4 14x3 Paper 791 CFM 91.9% 128
Moroso 97080 14x3 Paper 776 CFM 90.2% 131
Amsoil 52 14x3 Foam 774 CFM 90% 140
Purolator APF74 14x3 Paper 736 CFM 85.6% 146
AIS AF3 14x3 Paper 724 CFM 84.1% 148
Wix 42095 14x3 Paper 721 CFM 83.8% 149
Wix 42095R 14x3 Paper 712 CFM 82.8% 143
Fram CA136 14x3 Paper 710 CFM 82.6% 142
Edelbrock 1217 14x3 Paper 701 CFM 81.5% 154
NAPA/CompPol 22095 14x3 Paper 693 CFM 80.6% 155
Wix 42095 14x3 Paper 674 CFM 78.4% 163
Wix 46947R 14x3 Paper 595 CFM 69.2% 175
Air Filter Flow Test
14" x 4" Round Flow # @ 5" H2O % Flow Rating Swirl
Brand Part # Size Material
Wix 46944R 14x4 Glass 907 CFM 100% 116
AIS Cotton AF4C 14x4 Cotton 883 CFM 97.4% 116
K&N E-1690 14x4 Cotton 882 CFM 97.2% 121
K&N 61-4020 14x4 Cotton 880 CFM 97% 120
AC Delco 697C 14x4 Paper 825 CFM 91% 132
Accel (dry) 70004 14x4 Foam 820 CFM 90.4% 120
Amsoil 25 14x4 Foam 820 CFM 90.4% 131
Motorcraft FA705 14x4 Paper 814 CFM 89.7% 131
Wix 42096 14x4 Paper 813 CFM 89.6% 132
AIS AF4 14x4 Paper 803 CFM 86.5% 138
Fram CA3492 14x4 Paper 796 CFM 87.8% 126
MotoMaster 2330090 14x4 Paper 788 CFM 86.9% 135
Wix 42096R 14x4 Paper 786 CFM 86.7% 136
Wix 46946R 14x4 Paper 683 CFM 75.3% 155
I've considered those K&N's, but aren't they a bit pricey? I have the edelbrock 14x3 on my pickup for an air cleaner. Looking to change out the element (been a year, getting dirty), considering the NAPA gold 2095, but I am not sure how much that is, either.