K&N filter and worse MPG???

[sheipe05]

I have a 2001 Legacy. I installed a K&N air filter and it seems like I am getting worse gas mileage. I'm only getting around 21 miles per gallon mixed city and highway. Has anyone else had this problem? Thank You!!

Kevin

[jamal]

Maybe there's too much oil on the filter. I've heard it's fairly common. Also have you checked replaced the other obvious stuff like plugs, wires, and the fuel filter?

[sheipe05]

Yes, I replaced all of those not too long ago. I installed the filter straight from the box. I did not add any oil since it was pre=oiled from factory.

[TurboTbird]

Yes, I replaced all of those not too long ago. I installed the filter straight from the box. I did not add any oil since it was pre=oiled from factory.

 

Do you have a heavier foot from the extra power?

[1 Lucky Texan]

Well, I have a suggestion, but I feel it is unlikely to make a noticeable difference.

 

Reset the ECU. Either with a OBD II scanner or by disconnecting the neg. battery cable, tapping the brakes, waiting 20-40 minutes. Then reconnect.

 

It make take more than one tank to know if it helped because the ECU will need to relearn all the sensors from a 'standard' map starting point. This procedure is satndard for most changes to the emiisions,air/fuel system.

 

I will, say that the use of a K&N filter is still - um - controversial so you should be prepared for a negative comment or 2. Personally, I'm not convinced there is either significant proof of benefit OR detriment. More like a gimmick I suppose.

 

Also, there HAVE been instances of excess oil getting on MAF sensors and causing problems but it seems that would be unlikely with a factory treated filter and more likely with a user over-oiled filter.

 

Also, make darn certain the filter box is clipped back in place properly and no hoses were accidentally disconnected elsewhere.

 

let us know what you discover OK?

[jamal]

Do you have a heavier foot from the extra power?

 

 

I hope you're kidding

[NoahDL88]

 

I hope you're kidding

 

 

Thats a valid question, if anyone thinks they have more power from a K&N on a stock motor, its only cause they are now using a higher end of the rev band, so the motor only feels more powerful, when in-fact its not, and you are only using the more powerful end of the powerband.

[idosubaru]

i would be very surprised if you noticed a decrease in mileage due to the K&N. actually i woudln't believe it was because of the K&N unless i saw and tested it myself. accurate gas mileage comparison is tricky. conditions, weather, driving habits, weight of the car, condition of brakes, transmission, car all have to be similar to be accurate. that's hard to do unless you're really paying attention. the best gas mileage comparison i've been able to do is on highway trips. i used to drive alot of 500-1000 mile trips. i'd drive, replace something and make the same trip. good comparisons that way, but for normal daily driving i find it hard to get good comparisons.

 

cars are each different. i'll get the same mileage whether or not i use the cruise control or not in my XT6 automatic or XT6 manual. in my impreza OBS i get much better mileage.....like 4mpg better if i use my cruise control on a highway trip versus not using cruise control (just tested it last weekend on a 800 mile trip).

[cookie]

I always go to the same gas station. I was happy to see the only 29 mpg the other day I've ever seen on my 99 Forester. Then this week I got 22. I think it just clicked off a bit early last week. I usually see about 25 or a bit less in winter, so this is about right.

You really have to average mileage over a long period to get good numbers.

I would be kind of surprised to see much difference with a K and N, but it would be really easy and cheap to switch back to test.

[kimokalihi]

I'd have to say that adding a K&N filter on your car is a waste of money. They dyno those things in import mags and stuff but the difference is so minimal it's not worth the money.

 

Not to mention those companies pay the magazines to do good reviews on their stuff so I wouldn't believe half the stuff they say anyways.

 

In my auto class that I took last year both the mastertechs there told me you will NOT get an increase in hp with a K&N cone filter. I will believe them any day over a company trying to make millions off teen drivers. They'll tell you anything to make money. We live in a capitolist world and you have to watch out.

 

Think about it, if putting that filter on the car made as big of a difference as those companies say it does, don't you think they would do that out of the factory? Increased fuel economy!? Increase in HP?? They're all about Fuel economy!! Plus, when you put a one of those short rams on your engine it takes air from the engine bay instead of out of the fender or behind a headlight where it usually is stock. That air is much hotter so you will actually get LESS fuel economy and HP. Which is why I'm not suprised that you are experiencing less MPG.

 

Just my 2 cents. Passing on what they taught us at my AutoTech class. It wasn't a high school class either, it was a seperate technical school. My instructor told us this after visiting the Honda facility where they design all that stuff and they told him all that stuff.

 

Good luck with the filter.

[idosubaru]

you would think the "hot air theory" is correct, but it is not. Kevin has done extensive dyno testing on different intake set ups (among lots of other things) in the older gen forum. take a look at his plots, he's a no BS, doesn't beleive anything until it's dyno'ed type of guy (that's why he gets numbers). he proved lots of people wrong by showing some gains with a cone filter "in the engine bay". interesting read if you'd like to find his old posts on it. lots of dyno time too.

 

i agree, i wouldn't expect much with a drop in filter either. i do like the fact that i can run one for 200,000 miles.

[jamal]

yeah unless you're going less than 20-30 the temperature in the engine bay isn't a whole lot higher than outside. It does stay a bit warmer behind the motor though.

[idosubaru]

here's a post by kevin showing 1-4 hp gains...maybe even 10 on the one plot, i can't see it too well on my screen. interesting read though. now i don't know if this is a K&N filter, but it is removing the stock box and sucking in "hot air" and a similar cone style filter:

 

http://www.xt6.net/forum/viewtopic.php?t=1817&highlight=jc+sports+dyno

 

there are gains to be had. i'm pretty sure i had a small gain in highway gas mileage when installing my K&N years ago, but that was...well years ago.

 

the argument "if it's better the factory would have done it" doesn't apply. lots of things have some level of improvement that OEM choose not to implement for various reasons.

[WAWalker]

Not to be argumentative but.................................The "hot air theroy" is true. The fact is that cold air is more dense that hot air. There for with cooler air you get more air in the cylinder, and with proper addition of fuel, and ajustment of ignition, you can make more horsepower.

 

The removale of a restrictive stock air cleaner, housing, and induction tube, to be replaced with a less restrictive and better flowing system does nothing to prove horsepower gained or lost due to air temp, but says a lot for replacing stock intake parts with ones engineered to make more power.

 

And Subaru didn't do it because of the almighty $, less cost to build car more money in their pocket. It just a viscous circle now isn't it.

[idosubaru]

Not to be argumentative but.................................The "hot air theroy" is true.

 

what i said is true, a matter of semantics really. i was making a specific comment regarding this thread. in terms of a general theory that cold air is more dense, that's true but very generic and only part of the equation in practice.

 

in terms of this thread that variable is not driving the results. there are a few variables in play here and based on hard evidence that i posted links to, it is not the dominate factor. yes...gains are lost to heat, but improvements to the intake may offset those.

these are random numbers but make my point:

+10 for intake design - 5 for hot air still gives a gain of +5.

 

that being said, the OEM design runs a hot water hose right through the throttle body, heating up the throttle body with hot engine coolant. in theory, intentionally heating the throttle body and intake charge is a bad idea, but in practice it is insignificant. although i reroute my coolant lines anyway.

[nipper]

Air filter study. This comes up often enough it should be a sticky

 

http://www.ultimatesubaru.org/forum/showthread.php?t=41504&highlight=air+filter

 

 

nipper

[MDW25gt]

K&N filter will give you snappier throttle response.

[sheipe05]

I appreciate all the input guys! I didn't mean to start any arguments though The intake air temp should not have changed since I did not install the complete "cold air intake system" Kinda ironic being called the "cold" air intake system. I have put K&N air filters in every vehicle(and Quad) I've ever had and had some kind of increase in mpg and a little increase in hp especially climbing hills. For example, I had a Ford Ranger that got 20 mpg on my (mostly highway)trip to work every week. After the filter on the same trip I got just shy of 23 mpg. I guess it depends on the vehicle. I will try and reset the ECU as suggested. I will keep you updated. Thanks again!!

Kevin

[blitz]

on hard evidence that i posted links to, it is not the dominate factor. yes...gains are lost to heat, but improvements to the intake may offset those.

these are random numbers but make my point:

+10 for intake design - 5 for hot air still gives a gain of +5.

 

that being said, the OEM design runs a hot water hose right through the throttle body, heating up the throttle body with hot engine coolant. in theory, intentionally heating the throttle body and intake charge is a bad idea, but in practice it is insignificant. although i reroute my coolant lines anyway.

Gary, great dyno charts. My only two observations about the runs are that the revs begin at 4000-4500 RPM. In a dyno chart provided by Cobb to show HP gains with their straight ram-intake setup, it was obvious that the removal of the stock air-box created a huge hole in torque below 3500 in exchange for a slight improvement above 3500 RPM. Not my idea of practical commuting power, but for racing (in conjunction with a cam and exhaust) it would be sweet. The other thing is that the aluminum intake manifold can cost 7-8 ft. lbs. of torque depending on how heat-soaked it is. This is especially a factor at lower revs on account of the slower-moving air spending more time being heated in the runners of the manifold. I ofter wonder if the second of two dyno runs in a sequence will always show lower figures due to this.

 

**** ******!