Is bigger really better?
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Senior User
Joined: Nov 2008
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Is bigger really better?
Now that I have your attention ... 
I'm curious about the size of the air filter, not the type of filter as there is already a very interesting debate going on in the forums. I'm curious because I will be buying a new aircleaner for my 78 302.
This one is not very tall.
While we find your parts, please enter your ZIP Code at PartsAmerica.com
This one has a smaller diameter but is taller.
While we find your parts, please enter your ZIP Code at PartsAmerica.com
Here's an Edelbrock 14"
While we find your parts, please enter your ZIP Code at PartsAmerica.com
Let me know if those links don't work. May have to put a zip code in first and I apologize for that.
I'm curious about the size of the air filter, not the type of filter as there is already a very interesting debate going on in the forums. I'm curious because I will be buying a new aircleaner for my 78 302.
This one is not very tall.
While we find your parts, please enter your ZIP Code at PartsAmerica.com
This one has a smaller diameter but is taller.
While we find your parts, please enter your ZIP Code at PartsAmerica.com
Here's an Edelbrock 14"
While we find your parts, please enter your ZIP Code at PartsAmerica.com
Let me know if those links don't work. May have to put a zip code in first and I apologize for that.
Post Fiend
Joined: Jul 2006
Posts: 6,948
Likes: 44
I would be interested in joining a refreshing debate on this subject.
My flow bench data shows that the diameter of an air filter does not affect or limit air flow. All things being equal (material, cleanliness etc) and as long as the filter was larger than the carb throat, it did not make a difference in flow. The only difference it made was the intervals in which the filter required replacement or had to be cleaned. The larger filters would last longer because there was a greater amount of filtration area.
As a couple examples:
Engines with multiple carbs are limited by filter size simply because of the location of the carbs. Now I do know that there are filters that can accomodate three carbs under one filter, but there are also individual filters, and these as individuals will flow as much as the filter that fits all three.
Anyway, even a small filter is capable of flowing more than enough air to accomodate any internal combustion engine, as long as it is clean. Smaller filters will contaminate at a much faster rate.
Large filters bring "cool factor" but do not offer much in the area of horsepower gains.
My flow bench data shows that the diameter of an air filter does not affect or limit air flow. All things being equal (material, cleanliness etc) and as long as the filter was larger than the carb throat, it did not make a difference in flow. The only difference it made was the intervals in which the filter required replacement or had to be cleaned. The larger filters would last longer because there was a greater amount of filtration area.
As a couple examples:
Engines with multiple carbs are limited by filter size simply because of the location of the carbs. Now I do know that there are filters that can accomodate three carbs under one filter, but there are also individual filters, and these as individuals will flow as much as the filter that fits all three.
Anyway, even a small filter is capable of flowing more than enough air to accomodate any internal combustion engine, as long as it is clean. Smaller filters will contaminate at a much faster rate.
Large filters bring "cool factor" but do not offer much in the area of horsepower gains.
Senior User
Joined: Nov 2008
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If the air moving into your engine is traveling at a speed x, and your aircleaner has the same volumetric flow of the carb then that means the air traveling through the restriction (of the air cleaner) must also be traveling at that speed x. If you go to a larger air cleaner the speed of the air traveling through the restriction can be lower, thus your engine has to "suck" less to get the air. I agree with the statement that if it is clean this wont matter, but the problem is almost instantly they are somewhat dirty, there is no possible way to keep them 100% clean and as you said a dirty element that is small will restrict faster and more than a larger element. So in short, a larger element will be more beneficial to your engine, power, and fuel economy.
Lead Driver
Joined: Jun 2006
Posts: 5,654
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From: Near Yosemite CA
I bought my new one for my 73 based on the simple math of "replacement filter availablity and cost!" Looked through the book, see which size is more common, diameter wise, has more options to go taller, easier to get, more available or have in stock. And I do agree with 75F350, by the way.
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Senior User
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I see the benefits to having a larger filter, as it has more surface area to trap dust. The carb itself is only going to suck in so much air (max cfm), so I would think that eventually you would hit a size where the air cleaner could potentially allow more cfms, but your carb isn't going to suck in anymore than its max cfm. Therefore, the only benefit you're getting from huge air cleaners is the surface area to collect dust. The key then is to simply not restrict the airflow with a small cleaner, and either change your filter more often or buy the larger filter so that you clean it less.
And if you're concerned about airflow, you could potentially get a smaller air cleaner and get a k & n filter to allow more airflow. Make sense or am I rambling?
And if you're concerned about airflow, you could potentially get a smaller air cleaner and get a k & n filter to allow more airflow. Make sense or am I rambling?
Post Fiend
Joined: Jul 2006
Posts: 6,948
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Nah, you have it correct. Keep in mind that even a tiny air filter can pass far mow air flow than even a giant carb can. Also keep in mind that you carb can only flow up to the max size of the carb. I mean if you are running a 750CFM carb, it can only flow up to 750CFM at wide open throttle. You will not be at WOT 100% of the time, and even if you are, even a small air filter is capable of flowing over three times that amount. Restrictions only start to occur when the filter becomes saturated with dirt. As a matter of fact, the problem with contamination is not a real lack of flow, it has to do with the filters ability to resist dirt from passing. Particles start to pass through the filter and is permitted to enter the engine. Not necessarilly a decrease in flow. WHile one might see slight decreases in total flow, it is still not enough to decrease an engines performance. Even a fairly dirty filter (even a small one) will be capable of flowing more air than the carb is capable of passing through it and still capable of meeting an engines air demands.
The filter might have to be wet or something for a real decrease in flow to occur, but this is a completely different can of worms.
The filter might have to be wet or something for a real decrease in flow to occur, but this is a completely different can of worms.
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I ended up getting a 14" air cleaner. Didn't get the fancy edelbrock though 
I'm kind of sad now, nothing to do on the engine anymore. Now its onto wiring and interior restoration.
I'm kind of sad now, nothing to do on the engine anymore. Now its onto wiring and interior restoration.
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The problem is most people assume the engine and or carburetor pulls in air EQUALLY from all areas of the air filter.
Truth is the carb developes a favorite area to draw in air. If you look at a well used filter you will see areas that are dirtier or more clogged than others.
That applies to open element and OEM style air cleaners. Also applies to big rig semi and John Deere equipment. They all develop a favorite area to draw in air.
Want to extend the life of your filter a little? Rotate it.
Another thing this points out is even when that favorite area starts getting clogged, the engine will STILL try and draw air from that particular location.
Josh
Truth is the carb developes a favorite area to draw in air. If you look at a well used filter you will see areas that are dirtier or more clogged than others.
That applies to open element and OEM style air cleaners. Also applies to big rig semi and John Deere equipment. They all develop a favorite area to draw in air.
Want to extend the life of your filter a little? Rotate it.
Another thing this points out is even when that favorite area starts getting clogged, the engine will STILL try and draw air from that particular location.
Josh