Air Filters & MPG: the thread

Ok so spaceballs inspired the title.

We've all seen the threads around here about whether air filters (or pulling out the carbon trap) do anything for fuel efficiency and they pop up like weeds every spring. Typing up virtual weed killer is a real drag and a waste of time. I think it's time to make a thread we can point to!

First, why do we get this question? Well, it's most likely a throwback to the days of ye ol' carburetors and how sensitive their jetting was to air pressure. After all up in the mountains one would need to switch to a smaller jet (or jets) to run a carb that was originally set up for under 5000 feet.

"But we don't use carbs anymore, Jim! My truck haz been blessed wit de EFI, and air filter companies still say dey can improve my mileage by x percent!"

Well thanks boss. Isn't it wonderful we don't have to stomp that gas pedal every morning to choke it? However it does change the mechanics of the system. No longer is fuel mix distributed by a carefully engineered bias in pressure down the throat of the venturi. The computer does the math in real time by reading how much air the engine is pumping through, in our case with the mass air flow sensor.

Some decided to test how this changes things:

The EPA had a fairly thorough test... http://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf

Consumer Reports had their bit... http://www.consumerreports.org/cro/2012/01/fuel-economy-save-money-on-gas/index.htm

Time after time people keep finding that ~surprise~ the throttle plate is a far greater restriction than an air filter is! At least, whenever you're not booking it to Starbucks before you head to work. When cruising along, to maintain the manifold vacuum, that throttle plate is almost completely closed. The air filter never even needs to approach its maximum airflow capability to satisfy the needs of the engine.

"But Bob I don't believe it! Those are hack studies! Pulling the secondary filter gave me 2 mpg! These rules don't apply to Tacomas! My buddy told me..."

Alright, hold on a minute. Don't poop your pants just yet. I have a few dollars in my pocket I think I can use.


Why don't we examine an air filter more closely and maybe even start a wee experiment with it.





Mr Jackknife got to help out tonight. This was an STP SA9054 I bought for seven bucks. It's a typical inexpensive paper filter.

Let's compare it to the OEM Denso filter that Toyota will sell you for under $20.





...it's almost the same size! There are more pleats on the STP, but the Denso is more than twice as thick.

So how much filter area is on that 8.5"x9.5" filter?





Yikes! I bet you didn't think there was that much. I left 6 pleats on the filter (they were partly molded into the outer edge) and what I did cut out measured 10' 2" long. That should give a fair representation of what the Denso filter should be capable of.

Why does that matter? Well, in the world of science, you test extremes to determine trends, and thus I'm going to use this for my own little experiment:





This fits the 4" opening between the airbox and the connection tube to the fender. It'll get exposed to the dirty air and the stock filter can just sit in there for the ride. It should fit the definition of an extreme - if a filter that would provide insufficient airflow to a 22RE doesn't hurt mileage, how can the carbon trap hurt it or a cotton filter help it?

Yes, that's right. Out of an air filter with over 900 square inches of surface area I'm going to make all the engine's air go through 12.5 sq in of thick paper.

"George, you can't do that! You'll suffocate your 4.0L engine and get 10 MPG!"

Too late. It's already in.





Woah! That's smaller!

I took it for a ten mile drive just to make sure it was indeed driveable. Yes, it is! Surprisingly so. It is definitely an added restriction because it loses so much torque above 3500 rpm there's no point in trying to go there. It really gives a feel for how an air filter's flow affects the engine because despite the total lack of higher rpm flow, under 2000 rpm I can just barely feel it's there, even at full throttle. Still, the truck doesn't even approach the power output of the 4 cylinder 2TR - not even close.

Speaking of full throttle, it didn't get pulled out of it's spot after the test drive, did it?





Nope, its schwartz didn't even get twisted.

Now we need a baseline mileage to compare to. Fuelly gives the ballpark capability of this truck on my commute:





So stay tuned, don't poop your pants, and we'll see what becomes of it.

As an added bonus, it'll clearly show how much garbage runs up that intake tube, and whether you really want to trust a cotton filter to clean all that up. Besides, if it clogs up enough to be a problem and I need to replace it, I have another 9 and a half feet to cut 5" circles out of.

 

RESULTS SECTION

First tank: 274.6 miles, 11.822 gallons, 23.23 mpg.
Second tank: 268.9 miles, 12.289 gallons, 21.88 mpg.
Third tank: 298.8 miles, 13.191 gallons, 22.65 mpg.

Overall: 842.3 miles, 37.302 gallons, 22.58 mpg.

******

Conclusion: the extra restriction (that I am so very glad to have out now!) has no significant effect on mileage.

It also means I got this test done before winter gas hit... w00t! I was hoping that they wouldn't change it up before the test was done.

And now for used filter pics.




All in all not as dirty as I had expected, but it's been raining more days than not during these past three weeks. I imagine if this test was conducted this past summer when it was drought-dry and clay dust was everywhere it would look much worse.

The rain seemed to have an effect on the filter though:





It's permanently set in that shape and it's hard, like paper maché. I wonder if it got a little wet when I hit those massive puddles on the way to work last week. One caught me by surprise and I couldn't get over because of traffic but it was at least 6" deep and I traversed it at all of 30 mph.

And of course, a see-through pic, though it doesn't reveal much.





Thus the test is concluded and your weed killer is ready. Kill dem weeds!

 

sub'd for later reading. thanks

 

Two observations so far:
-engine load is calculated by the ultra-gauge from TPS. I'm quite sure. My normal load at 55 mph is about 40-42% and it has been staying around 50-55% with the mpg reading normal. Warm idle is now 33%, without extra filter normal was 28%, but both before and after have read 0.33-0.34 GPH fuel flow rate.
-ignition timing is definitely NOT derived from TPS. Must be directly from the MAF. It's running the normal 29.5° at 55 mph on the flat, 30° at 59 mph. That means all arguments about improving mileage by taking measures to reduce throttle angle to artificially bump ignition timing are out the window. If overall mileage is in the norm than it should be a safe bet to assume VVT is controlled based upon MAF data as well.


First tank is up, 23.2 mpg. Not too shabby considering it includes two mornings with frost advisories.

It's a shorter distance that what I've been putting on tanks but after careful deliberation the reasons for which I've posted in the 2nd gen forum I'm aiming for 12 gal burned per tank (UG said 12.1 at time of fill, as usual it overestimated a bit).

Another random tidbit, for those that claim you can't get good mileage under 55 mph, I LOL in thy general direction. This was about 8 miles from the gas station to home in traffic with slow speed limits (mostly 30 to 45). For those who don't look left, yes it IS a 6 spd 4.0L 4x4.

 

sub'd as well.

 

i don't even like pop corn i just wanted to write on this so i can click my recent post and find this easier, and thought might as well. interesting test so far.

 

Can somebody tell me how to subscribe to a post without posting on it??? I want to be able to come back to this one, thanks.

 

On the top right of the thread click the drop down menu that says "thread tools". "Subscribe to this thread" should be an option.

 

thank you

 

Second tank is in, 21.9 mpg. Took a bit of a dip from the hard frost mornings and helping some friends move some stuff from their old house, but still well within the norm.

Last tank started... I can't wait to get my horsepower back!

 

What's the name of that there device? I'd like to get one for my 4runner, I don't trust my gas gauge enough to even guess what I get for mileage.

 

It's an Ultragauge. About $60.

http://www.ultra-gauge.com/ultragauge/index.htm

 

Third and final tank is in. 22.65 mpg. Overall all miles and gallons divided is 22.58 mpg, which is above my fuelly all-time average and within the norm for what the truck has been doing the past few months.

filter pics are hiding up in post #2.