What air filters are you using?
What air filters are you using? I put a filter on my car that turned out to be too small. I contacted Airaid and aFe and neither of them know the CFM of their filters or can tell me how to calculate it. The best information I can find is on K&N's site with lists 6.2 CFM per square inch, but they do not go into detail as to whether that is a flat surface or a pleated surface.
It got me to thinking...I wonder how many people are running a filter too small on their car and losing a lot of hp because none of these filter companies even know what their filters flow? That high performance filter may flow less than the paper factory job you chucked in the trash.
It got me to thinking...I wonder how many people are running a filter too small on their car and losing a lot of hp because none of these filter companies even know what their filters flow? That high performance filter may flow less than the paper factory job you chucked in the trash.
Ok. aFe does not have CFM information according to what they told me. I wanted the Pro5R media.
K&N seems the best, but they do not have a filter in the size I need unfortunately.
K&N seems the best, but they do not have a filter in the size I need unfortunately.
Trending Topics
I've always ran K&N and never had an issue.
kPa dropped with the paper filter always... Robbed about 10rwhp and 8ftlbs on the dyno, and enough to feel on the street in the upper RPM's
kPa dropped with the paper filter always... Robbed about 10rwhp and 8ftlbs on the dyno, and enough to feel on the street in the upper RPM's
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Anybody know how they check cfm? The K&N site has a nice write-up, but it seems a bit confusing. If they say your filter flows 1000 cfm, is it assumed that is at 1.5 H2O?
aFe told me an 8" round cone filter 7" long that tapers to 7" has a flow of 312 cfm at 1.5 H2O. There is no way that big of a filter would only flow 312 with air.
aFe told me an 8" round cone filter 7" long that tapers to 7" has a flow of 312 cfm at 1.5 H2O. There is no way that big of a filter would only flow 312 with air.
TECH Addict
Joined: Feb 2012
Posts: 2,103
Likes: 21
I believe there are industry standards on testing airflow through a filter media. Check around and or ask K&N what test procedure number they use. Most likely get in touch with tech support or product development.
You ASSUME that a OEM filter flows enough for the required flow rate of your motor at Max TQ. Then you assume that a K&N drop in panel filter is even more efficient due to different media they use...hence the power increase you MIGHT see.
SO calculate the area of a OEM size panel filter as a starting point to be the minimum filter area you need. Again assuming you have a stock motor.
You can calculate the CFM your motor needs. Then size a filter to accommodate that value. I did this a while back. I then called K&N to confirm my number then went searching on their website for a filter in the correct size that also fit my application/space.
Filter selection is only part of the equation. Intake duct design will also play a role in kPa values dropping throughout a dyno pull. Resonant frequencies at certain RPM's etc.
You can also do a little experiment hooking up a shop vac to a home made manometer to test filter/intake tube efficiency. It's not an accurate test but all you want to see is a delta between tests. You want to see the least amount of height difference between the sides of the manometer between different designs....this would represent the least amount of intake restriction or pressure drop.
You ASSUME that a OEM filter flows enough for the required flow rate of your motor at Max TQ. Then you assume that a K&N drop in panel filter is even more efficient due to different media they use...hence the power increase you MIGHT see.
SO calculate the area of a OEM size panel filter as a starting point to be the minimum filter area you need. Again assuming you have a stock motor.
You can calculate the CFM your motor needs. Then size a filter to accommodate that value. I did this a while back. I then called K&N to confirm my number then went searching on their website for a filter in the correct size that also fit my application/space.
Filter selection is only part of the equation. Intake duct design will also play a role in kPa values dropping throughout a dyno pull. Resonant frequencies at certain RPM's etc.
You can also do a little experiment hooking up a shop vac to a home made manometer to test filter/intake tube efficiency. It's not an accurate test but all you want to see is a delta between tests. You want to see the least amount of height difference between the sides of the manometer between different designs....this would represent the least amount of intake restriction or pressure drop.
I did ask K&N. No reply. I also called an d got put on hold indefinitely when they went to "check with our engineer" about the answer.
The issue is...what is the CFM rating of the filters? Calculating out the CFM your engine needs is relatively easy, and you can calculate out roughly the size filter you think you need, but without the CFM values per square inch for media they use, it is all worthless. K&N states "roughly" 6.2 CFM per square inch, but the do not elaborate on whether that is a filter laid flat out or if that includes the pleats? A filter 1.25" thick is going to flow a lot different than a filter that is .75" thick, and they make them both. Laid flat out they are probably close.
Considering some of the numbers I have seen or been given, I would guess a lot of people probably have filters that run out of CFM long before their engine does. Considering manufacturers like Airaid do not even have CFM numbers for their filters, you really have no clue whether that filter you are buying flows even the same as your original filter nevermind better.
The issue is...what is the CFM rating of the filters? Calculating out the CFM your engine needs is relatively easy, and you can calculate out roughly the size filter you think you need, but without the CFM values per square inch for media they use, it is all worthless. K&N states "roughly" 6.2 CFM per square inch, but the do not elaborate on whether that is a filter laid flat out or if that includes the pleats? A filter 1.25" thick is going to flow a lot different than a filter that is .75" thick, and they make them both. Laid flat out they are probably close.
Considering some of the numbers I have seen or been given, I would guess a lot of people probably have filters that run out of CFM long before their engine does. Considering manufacturers like Airaid do not even have CFM numbers for their filters, you really have no clue whether that filter you are buying flows even the same as your original filter nevermind better.
I love math too much to let anyone else do any.
The simple solution here, is to use an OEM dry paper element or similar for all daily driving situations/traffic and so forth. 99% of the time run the paper for best protection. If you care about the engine.
When you go to the track or need to win a race or something, switch to a better flowing, less "filtering" filter. I would never run without a filter. Filters tend to smooth the airflow and I have seen engines pick up WHP after installing them, where there once was none, especially on turbochargers, which will appreciate inlet ducting/filters.
Another less obvious solution for high output engines that you (care) alot about, is to 3d print or otherwise custom fab an air box to contain multiple paper elements, or to use a larger paper OEM filter from another vehicle. Street cars are all about filtration, blanket, wrapping, coating, temp control and pure liquids/air.
The simple solution here, is to use an OEM dry paper element or similar for all daily driving situations/traffic and so forth. 99% of the time run the paper for best protection. If you care about the engine.
When you go to the track or need to win a race or something, switch to a better flowing, less "filtering" filter. I would never run without a filter. Filters tend to smooth the airflow and I have seen engines pick up WHP after installing them, where there once was none, especially on turbochargers, which will appreciate inlet ducting/filters.
Another less obvious solution for high output engines that you (care) alot about, is to 3d print or otherwise custom fab an air box to contain multiple paper elements, or to use a larger paper OEM filter from another vehicle. Street cars are all about filtration, blanket, wrapping, coating, temp control and pure liquids/air.
I have been running a K&N for at least the last 5 year. I keep it well maintained oiling it regularly. When I pulled the 102 apart to port it there was a lot of fine grit on the inside of the intake.
Just picked up a Wix to see how that works, leave the K&N for the track.
Just picked up a Wix to see how that works, leave the K&N for the track.