Seems evident that the more air filter surface, the better the breathing. But I've seen some pretty small filter elements on big carbs. What are the pros and cons for air filter size? Don't mean to get into extreme hi-tech situations. Just whether or not if bigger is better on air filters or if one too small could hamper performance. THANKS !
If it is too small, it will hurt performance. Too big, and it just gets in the way. Contact a filter mfg for help... or search the web as I suspect there are sites that will help you calc up the CFM needed. Gary
Bigger is better but you won't know exactly how big unless you know the flow charactistics of the filter element and the engine requirements.
Air filters should, at least, have flow capacity to matched the engine's needs. Failure to select filters sized large enough is detrimental to optimum performance AND economy. A secondary benefit of a filter with larger than needed surface area is longer time before replacement or cleaning.
Guess there's more variables than can probably be covered. I'm working with a combo ram cold air induction with a filter that is smaller than I want to use. Trying to keep a traditional look which restrains the size in keeping it hidden. So I'm ramming air into the filter along with the vacuum the carb has. Just figure I'll be changing filters more often.
Hot Rod Magazine (I think) did a dyno test on exactly this question a while ago. The results were a little surprising. There were minor differences between the different diameter and depth of air cleaners, but not as much difference as you might think. The article was within the last three or so years.
Guess that's why I've seen smaller air filters on dual quad setups on top of monster high rise intakes and such. I suppose it also depends on the amount of open air they are catching. High output engines of the early to late 60's had shallow, but large diameter housings that still only suck air in through a small opening at the end of a long snorkel. Hot rodding is all about trial and experiment. But I have no loss of pride to ask about what others have learned. In some cases, we have to rely on precision guesswork..........
The only time it would hurt performance is at full throttle unless it's way undersized. Just like you gain nothing from a K&N unless your full throttle.
Hi Woosh! I like that..."precision guess-work"! Hahahaha! Nothin' like takin' 'er out on the road, and doing some "seat of the pants" testing. Take the air-cleaners off...run it. Put the air-cleaners on...and run it again. See ya pal.
I always saw it as a bigger one can get dirtier or last longer than a small one. The small ones flow good new but get dirtier faster , thus really ruining the performance.
Good question, i've wondered the same thing. I only have a two barrel but just didn't know if such a tiny filter like the one i have on there right now would be good enough. thought i would be changing it all the time. when i saw it, i thought it was for a mc. lol (give me a break, i'm still learning guys) Also, has anyone ever used the large round stock oil bath filters and rigged them to make them work with regular air filters? would that work or would it not grab enough air? Was thinking of trying that since I like the look of the original oil bath filter instead of the small shiny silver air filters. just was curious.
Smaller filters will clog faster than larger ones, given the same carb cfm. As filters load up, the pressure differential across them increases, which decreases the engine's ability to draw air through them. The bigger the filter element, the better.
for a trial and error guestimate on filter size, this may not be do-able if its torn apart but it may help ... plumb a vacuum line fitting into your cold air induction tube between the filter and carb/throttle body, hook a vacuum guage too that fitting, route the guage so that you can see it while driving and go for a ride. If it pulls a vacuum reading on the guage you probably need more filter. To validate the test results and confirm need of larger filter, remove filter and repeat the test with same driving conditions should now have no vaccuum reading
i have been drag racing my falcon for years and have had everything from cheap kmart paper filters to expensive k&n filters. i have never had a change in mph or et by changing air filter size or brand. so now i go by what looks best under the hood and dont worry about it.
Don't try to run a filter that is too short as the distance between the air horn (choke stack) and the under side of the cover is also important. A well designed air filter does more than filter the air. It also plays an important role in straighting and smoothing out the air flow. I learned something long ago about air cleaners with a snorkel. Don't point it straight forward. The air flow under the hood of most cars and above the the engine is back to front. Learned this the hard way racing '55 -'57 chevys.
CrkInsp. Good point. Air direction and deflection isn't always what we would suspect unless we take a ride under the hood. All the air going into Nascar engines is coming from a fairly small opening at the base of the windshield. Pretty much like vintage cowl induction. I'm running a similar set up through the ventilation screen at the base of my windshield. Diverted the cool air that was for Summer ventilation to the interior to the carb instead.
From K&N sile and more info http://www.knfilters.com/filter_facts.htm#FACTS Use the formula below to compute the minimum size filter required for your particular application. 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. <CENTER><TABLE border=0 cellPadding=10><TBODY><TR><TD> </TD></TR><TR><TD>A = effective filtering area CID = cubic inch displacement RPM = revolutions per minute at maximum power </TD></TR></TBODY></TABLE><TABLE border=0 cellPadding=10><TBODY><TR><TD>Example: A 350 CID Chevy engine with a horsepower peak at 5,500 rpm.</TD></TR><TR><TD> </TD></TR></TBODY></TABLE></CENTER>If you are sizing a panel filter, multiply the width of the filter area (not the rubber seal) times its length. If you are sizing a round filter, use the following formula to determine the height of the filter. <CENTER><TABLE border=0 cellPadding=10><TBODY><TR><TD> </TD></TR><TR><TD>A = effective filtering area H = height D = outside diameter of the filter 3.14 = pi 0.75 = the rubber end caps </TD></TR></TBODY></TABLE><TABLE border=0 cellPadding=10><TBODY><TR><TD>Example:</TD></TR><TR><TD> </TD></TR></TBODY></TABLE></CENTER>Referencing the K&N catalog shows the proper filter for this application would be an E-1500 which is 3.5 inches tall. Keep in mind, this is the minimum size requirement. To extend the service interval and to provide an even greater volume of air to the engine, install the largest filter that will fit in the space allotted. If the space above the engine is restrictive, perhaps a remote filter arrangement could be used to gain space. Off-road conditions require added filter area. A filter should be sized 1-1/2 to 2 times larger than normal for any conditions that could be considered severe. In this case, the E-1500 used in our example should be replaced by an E-1120 or an E-1150. For long distance off-road events, two double-size remote mounted filters would be best. Vergil
Christie To answer your question about the oil bath to paper filter conversion, several companies are putting out the mid 50's batwing air cleaners to work the paper filters without doing a thing. I did it the hard way and converted an original to house a monster filter inside with direct flow across the face instead of just the horns. Won't meet with everyone's approval, but suites me and the car.... Be creative. It's FUN!
SirWoosh, If you go to a locald dirt track and watch the stocks or modifieds run .Notice there air filters.Usually 3 to 4 inches tall, Any driver there running up front will tell you the same answer. The bigger diameter and taller filters have more area to collect debris and don't clog as quickly.Also once the air is in the filter it has more time to calm and flow into the carb more evenly.
Yep, know what you mean lowkroozer. I'm only a few miles from one of the top dirt tracks in the country. They generally duct tape the forward face of the filter. Don't last long on dirt either. I run large filters whenever I can. I just have an enclosed ram air on the one car and am restricted for size. Check a few posts up at the modified batwing. I've got a sprint car filter in that one. Thanks!
Thank you! i didn't know about those batwing paper filter ones OR maybe if i'm feeling brave i'll pull out the cutter and get creative like you said. we'll see...
It's been my personal experience that a restrictive air cleaner will make a noticable negative effect on midrange power near where the engine makes maximum torque before top end power is affected .Reading carburator tuning guides it's mentioned that a restrictive air filter makes the part throttle mixture go lean ,not rich.
Size does matter, so does quality. K&N's have more surface area, filter more efficiently, and can be cleaned. They also flow better than your regular paper filter. This effects at all throttle positions. Sounds like you really don't have a handle on what your engine is doing then. I've seen dyno runs that prove otherwise. I even did quite a few dyno tests when I was building racebikes and there most definitely is a difference and it shows up in jetting across the board.
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