View Full Version : CFM of air filter

01-04-2015, 08:25 AM
I have a stock Autolite 2100 carburetor that is rated at 240 CFM.



I bought a Purolator Classic Round Air Filter A30057 for $7.59, at Advance Auto Parts that is an "Exact fit for your 1963 Ford Falcon".


But, ... the air filter is rated as 120 CFM. :WHATTHE:

See: http://www.sc-liquidations.com/product_info.php?products_id=10300
See: http://www.niparts.com/MAC/0FDEBA/PUROLATOR/A30057.html

Why is the filter only rated for half of what the carburetor will draw?

I would like to have a filter with a capacity that matches the carburetor.
When I bought my car it had a 500 CFM four-barrel Edelbrock carburetor and an aftermarket "high performance" air filter cover that contained a NAPA Silver filter, Part No. 22095 O.D.: 13.875”, Height: 3.087”. As an experiment, I tried putting it on my Autolite carburetor, but the center stud was too short. I bought a NAPA 6037 filter (Wix 46037) with the same O.D.: 13.875", but with a lesser 2.64” height and it fit.



Unfortunately, I afterwards found that this filter is rated for 215 CFM.
See: http://www.fleetfilter.com/filter/wix-air-filters/46037.html
215 CFM is an improvement over 120, but I am still looking for a filter that will get me to at least the magical 240 CFM.


01-04-2015, 11:23 AM
Uhhh, ... the solution should have been obvious.
I unscrewed the mounting stud a little bit. :)

That enabled me to install a $7.99 Wix 42095 air filter that is rated at 250 CFM.
See: http://www.oreillyauto.com/site/c/detail/WIX0/42095.oap?year=1985&make=Buick&model=Regal&vi=1446425&ck=Search_42095_1446425_4313&keyword=42095


I didn't hear a crash of metal when I slammed the hood down, so I think that I am good to go!

This shows the difference between the smaller stock Purolator A30057 air filter and the larger Wix 42095 filter.


I understand now why different air cleaner covers were used on the Falcon Sprints. That was functional and not just cosmetic.

Post Script: I wondered what the CFM rating meant. It turns out to be the peak air volume at which the filter will provide its rated filtration. That means that the smaller filter will not necessarily limit flow past 120 CFM, but its filtration efficiency will not be assured past that limit. On my Falcon, 120 CFM corresponds to around 50 mph. That means that the larger filter will provide better filtration while traveling above 50 mph and that better level of filtration would continue up to 100 mph, but it will not necessarily provide any more air flow, or power, or speed. The bottom line is that any advantage from the larger filter is small. It provides better filtration while at fast highway speeds, but that is about it. And since I don't do a lot of sustained high speed travel, it really doesn't make any difference. Oh, well. Once again, I cannot outsmart the Ford engineers who designed all of this to begin with. That's why I like the Falcon. Everything seems to have been well thought out.

The open design air filter cover does provide an advantage in allowing an easy visual inspection of the filter and it also weighs three pounds less than the original style cover. It does not protect the filter from getting wet, though, and the open design might also allow more engine noise to come up through the carburetor.