Over the last ten or more years that I've been posting on various automotive web sites I've managed to get myself embroiled in any number of discussions surrounding whether a clean air filter will allow a modern fuel-injected engine to deliver better fuel economy versus a dirty/clogged air filter. If any of you have seen any of those discussions (here and on other boards), you know that I have steadfastly maintained that regardless of whether the filter is so clogged the engine is about to be choked to a stop, or whether the filter is fresh out of the box (or for that matter, if there is no filter at all), that fuel economy will not be negatively affected. In fact, I've gone a step further and suggested (with nothing other than my intuition to go on) that a severely clogged filter may actually improve fuel economy by a tiny bit.

To say that my claims have often been challenged (vehemently so in many cases), is quite an understatement.

Well folks, here I am once again making those claims; the difference this time is that instead of providing factoids gleaned from countless engineering studies and SAE papers on various internal combustion engine topics, I am presenting y'all with a study that I've recently run across produced by the Oakridge National Laboratory and the Department of Energy that speaks directly to my claims.

http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf

So, unless I'm seriously misreading the study, fuel economy cannot possibly improve by replacing an old/dirty air filter with a new clean one.

Comments?

 

i will preface this by saying that i hate statistics. if you stretch anything out over a long enough time, you can find favorable results in anything at all.

now, on to my opinion. the air filter isn't the bottle neck in the stock intake system. the tubing before the air box and filter is intentionally restrictive for the sake of keeping water and debris out of the filter. i don't believe that an air filter is going to affect the fuel economy in one way or another.

my driving conditions and habits don't change at all on a daily basis. i drive the same route in the same car every day. it isn't a car that i drive in my free time. it is work only. my mileage varies between 25 and 35 mpg without any odd variables. i could take a little slice of those stats and say that my car gets 35 mpg or take another slice and say that it gets 25 mpg. i get the same gas from the same station once a week (twice if i only get 25 that week) and have an exact routine that i follow. statistics can easily be manipulated for favorable use. statistics on gas mileage have constantly been manipulated over these last few years.

if you accept as postulate that a CAI won't gain any mpg, you have to accept that a more restrictive intake won't gain any either. engine management makes all of the difference in a modern car.

poor vehicle maintenance is something that i don't take lightly, so you may have to excuse my tone here. cheap or expensive filters don't make a difference. they are all going to break down eventually. i have owned cars that filters have come apart little by little from not being replaced. i used to just rinse filters and leave them to dry on my daily drivers, but i have had a couple come apart from doing that. i replace them now.

 

wouldnt a new/clean filter cut down on emmissions? i mean a completely shut off filter(in DUST BOWL OKLAHOMA that can happen ) would make the car sputter and probably die.replace the filter with a piece of cardboard and see what happens.the AIR box on my milly S has a few vacumm hoses coming off of it so wouldnt a restricted/dirty fliter affect vacume to the maze of hoses and solenoids that rely on vacum at that box? i say just change the filter,its probably the easiest job to do to a car.ive spent more time reading about this taday than it takes to change about 15 air filters.it does make sence that the computer will take over and send the correct fuel but only to a point.when your foots to the floor and you can only go 45mph on the highway,sure youll get good gas mileage i guess

 

No, a new filter will not make one iota of difference in vehicle emissions, errr, unless the filter is so dirty the engine won't run at all (at which point you have zero emissions).