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Discussion Starter · #1 ·
I hope I'm not setting myself up for disaster by asking, but what is the issue? I've read a few posts that indicate disaster upon installation of a high-flow filter. It seems that the common concern is lean operation and potentially knock? I've read that the air intake isn't the bottleneck until a stage 2 or 3 level, so I can't imagine that it would flow a lot more air. What causes a higher flow filter to result in lean running? Is it related to MAF contamination? I guess I'm just surprised that a modern engine control system with knock sensor can't adjust AF and timing enough.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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to my knowledge, it comes down to problems with over-oiling (MAF contamination being the worst) and perhaps higher silica in oil analyses (check out bobistheoilguy.com)

I'm not a big hater - just skeptical that there's a measurable improvement or savings for the average person. Yeah, I dunno at what 'stage' it's required either if you're 'tuning'.

Plenty of people run 'em OK I guess. And maybe folks that offroad a lot in dusty conditions might save a little money cleaning/oiling their K&N.
 

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I haven't done the search myself but after checking the filter in my new (to me) 3gen and finding it horrendously dirty I was considering a high flow filter.

I do know from my Chevy days that the oiled filters (K&N et al) are generally non-conducive to a long MAF life. Therefore, for many cars there are new high flow dry filters available.

The question (as stated by Texan) is whether or not it's worth it. I don't plan on modding my 2.5 very much and as such will likely stick with a stock paper unit for at least the time being.

$.02
 

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2008 Outback WGN 2.5i Auto
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4 years no problems

I don't know what the fuss is. I've had a K&N Filter in my 2008 Outback for four years now with out a problem. I also put one in my 2003 Outback, my wifes 2008 KIA Sportage, and 2012 Ford Mustang and have not had a problem. I make sure to not over oil them. I also let them sit over night when I can. That could be the difference. As for performance, on the Outback's and KIA, there was no real noticeable difference. The Mustang actually did run better and the automatic transmission was better as well. My two cents this AM.
 

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Discussion Starter · #5 ·
That's a more positive reply than I was expecting. Or at least less negative. I've used then in previous cars with no problem. I have the oil and cleaners on hand already because of my old motorcycles that I've long used K&Ns on. So I like #1 not having to run to the parts store and find my filter, and #2 not having to pay for them regularly. I can't say I've ever noticed or claimed performance, but I like the longevity. My brother-in-law still thanks me for the K&N every time he cleans the filter in the '97 Accord I sold him years ago.
 

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05 OBXT 5eat stg1.2
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Don't do it. There is a huge difference between the xt and 2.5i. With the xt, it isn't an over oiling issue, it's a maf scaling issue. It will throw off the maf scale which will cause a lean condition. The way the ecu works, it is unable to accurately compensate fueling at high loads, so throwing off the scaling will lead to knock unless you have a very conservative tune. The stock tune is prone to knock even with everything stock. The k&n will only make that issue worse.

Long story short, anyone who has used one and actually logged has seen knock that was not there with a stock filter. This includes myself as well as some other people who were very skeptical of the negative effects.

We have the ability to log many things with the xt and just a vag-com cable, so it would be very irresponsible to do a mod like that and not make sure everything is ok.
 

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'07 OBXT Ltd. 5EAT, Charcoal Gray; '70 Chevy K10 4X4, 396c.i., lifted; '63 Pontiac Tempest, 326c.i.
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I purchased an '07 OBXT 5eat in February with 85K miles that had a K&N drop-in filter, but was otherwise "stock," according to the Toyota dealership. The salesman said it was a 1 owner, old lady that owned the car before I did. This begs the questions: 1.) Did she re-map the ECU, 2.) how long has she had it in there? 3.) What grandma puts in after-market parts?!

There are no apparent problems with the car at this point (now the car has 92K miles.) I can tell you that upon buying the car, I checked out the filter and it is showing signs of wear. If I had to guess, the filter had been with the car for at least 20K miles before purchasing. I doubt the ECU was flashed, but had no "control" car to compare against. I guess I'll know as soon as I look at my "stock" map.

Take what you want from my reply. I'm not saying to go ahead and do it. But I am saying that my XT has no problems with a stock tune and aftermarket drop-in filter. I have not experienced a knock. Then again, I can't be 100% certain of my car's history, but have probable cause to believe what I believe. From my limited knowledge of cars, here's what I know: the MAF senses the air flow, sends the info to the ECU, and the fuel supply is adjusted according to how much air is flowing. I am skeptical of anyone saying this will make a huge difference. However, I believe wholeheartedly that flashing the ECU is the best decision.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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I purchased an '07 OBXT 5eat in February with 85K miles that had a K&N drop-in filter, but was otherwise "stock," according to the Toyota dealership. The salesman said it was a 1 owner, old lady that owned the car before I did. This begs the questions: 1.) Did she re-map the ECU, 2.) how long has she had it in there? 3.) What grandma puts in after-market parts?!

There are no apparent problems with the car at this point (now the car has 92K miles.) I can tell you that upon buying the car, I checked out the filter and it is showing signs of wear. If I had to guess, the filter had been with the car for at least 20K miles before purchasing. I doubt the ECU was flashed, but had no "control" car to compare against. I guess I'll know as soon as I look at my "stock" map.

Take what you want from my reply. I'm not saying to go ahead and do it. But I am saying that my XT has no problems with a stock tune and aftermarket drop-in filter. I have not experienced a knock. Then again, I can't be 100% certain of my car's history, but have probable cause to believe what I believe. From my limited knowledge of cars, here's what I know: the MAF senses the air flow, sends the info to the ECU, and the fuel supply is adjusted according to how much air is flowing. I am skeptical of anyone saying this will make a huge difference. However, I believe wholeheartedly that flashing the ECU is the best decision.
she may have a had a son, or perhaps grandson, that was 'helping' her with her car maintenance.
 

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I put a K&N in my 2001 because it was nearly impossible to find the right replacement filter for it at the local auto stores and paying the dealer 200% mark up was of no interest to me.

2.5 non turbo - worked fine though I as cautious not to over oil it during the cleaning process. 180,000 no issues and nothing abnormal regarding grim build up past the filter.

Turbo on the other hand I would be cautious per Seabass comment regarding impacting the scale the MAF uses on the turbo intake. 250HP in a family wagon is plenty at stock configuration for normal every day use why mess with the aftermarket stuff unless you want to play with the car and retune it for more power etc.
 

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2008 Subaru Outback 2.5XT, DDM HID 5000K, K&N, Yokohama Avid TRZ, Curt Hitch, Subaru All Weather Mats, Sirius
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So i'm somewhere in the middle on this. I have a 2008 OBXT that i purchased at 32000 miles. I immediatly put a K&N in as I had used one on my previous MZ3 and was happy.

I had no issues for the 10k or so miles that I used the filter. However, as I started to do more random driving in dry, dusty or sandy conditions I became concerned about the ability of the K&N to capture or elimate this. In effect this would cause the higher silica count in the oil.

In the end I decided to stop using my K&N in favor of disposable filters. Once I drive around in dusty conditions I just grab a new filter. In the end they are far cheaper than an oil change and I still can change them every 3rd or 4th Oil Change.

I never noticed any difference between the filters from a performance perspective. However, I can say the 'disposable' filters always have far more dirt and debris in them compared to when I used my K&N so I have always wondered what makes it though.
 

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05 OBXT 5eat stg1.2
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And once again a bunch of people saying there are no apparent problems without hooking up a computer and checking what is going on. Just because you don't hear knock doesn't mean it's not there. Just because there has been no damage yet doesn't mean there won't be. It also doesn't guarantee that there will be damage.

There is not going to be performance gain by switching to a k&n, but it will throw off the maf scaling enough that a stock tune will knock at high load/high rpm. Do some research into how altering the flow, shape, etc of an intake can throw off a sampling maf.
 

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Although I have not done any racing mods to my 01 OBW, I put a K&N air filter in it at 101K and it now has 195K with the same K&N filter. I've had to clean it a few times but I knew that was my goal instead of eternal replacing.
 

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Yep, I never bought insurance and my house never burned down, so I know it's just as good not to buy insurance. Just as useful as the reasoning on this thread.
 

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Been using K&N for years with no issue but those were all non turbo engines. Just replaced the MAF on my 98 Impreza. Hard to tell the cause but I can't rule it out because I tend to over oil. My 2000 OBW runs much smoother in the lower RPM range with a K&N which is what I was looking for. Not much of a top end guy but don't have a turbo either. This would be a good time to use my fancy code reader to get some live info on the engine. If it really does make the XT's run lean you should check it out. That's not good. I don't have a problem with the air filter but this issue is worth looking into. Who knows, you might learn something new.
 

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If any engine management system can not cope from a new clean air filter to a old partially blocked system, and anything in between, it is the problem.

K&N oiled type filters obviously can cause problems with any "hotwire" type sensors if over oiled, but if the vehicle takes a little water through the Air pick up, I would sooner have a metal/cloth type filter protecting the engine than a piece of folded paper !
 

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First some history;
In the 60's Baja racers and others who raced vehicles in the desert were having filter clogging problems with paper filters. Enter K&N whose filters took far longer to clog. Now back then , racers expected to do full engine rebuilds after a race. Nowadays, Oiled foam has replaced K&N in most all powersports applications.
Personally, from experience I have lost a street engine at least partially because of a K&N. It began to smoke after about 40k and when I tore it down I found dirt throughout the intake and scored cylinders. The only mods were a Weber carb, header and K&N. I rebuilt the engine and replaced the filter with a oiled foam filter. It ran perfectly for another 200k until I sold it.
You are far better off using a stock filter or if you want something you do not have to replace as often, use an Amsoil Cellulose filter. They are rated to 100k and can be cleaned. I will never use a K&N product again. BTW if they are so good, then why do they say they filter better when dirty? That's because the dirt helps keep other dirt out. Crap.
 

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After being in the moto business and specializing in dual sport applications, we never recommended K&N's and would only "allow" their implementation on street only bikes. Why? Because they don't filter dirt for s***.
 

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If any engine management system can not cope from a new clean air filter to a old partially blocked system, and anything in between, it is the problem.

K&N oiled type filters obviously can cause problems with any "hotwire" type sensors if over oiled, but if the vehicle takes a little water through the Air pick up, I would sooner have a metal/cloth type filter protecting the engine than a piece of folded paper !
It can cope with the typical range of a paper filter being clean or clogged. The scale is set around a clean filter. It should be dead on when it is clean. As it gets dirty, the ecu will compensate as much as it can, but at some point will be off. In that case, it will be sucking less air in than it thinks. AFR's will be slightly rich in the higher ranges. Having afr swing .2 on the rich side shouldn't cause any problems. Swing it .2 in the other direction and you can easily get detonation on a knock prone engine with very aggressive timing.

This is just as much a problem on the aftermarket dry filters. Again, it is specific only to turbo models. I don't know enough about the logic used in the n/a ecus.
 

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I use a drop-in on my 2010 OB 2.5 and '03 330Ci because it's convenient and needs cleaning less frequently. I don't expect serious performance gains, I just expect long life and convenience. There's a factory non-removeable charcoal filter behind my OB's filter which shows anything getting through, and there's not a spec of red oil on it. After using a full K&N cold air intake on my old SRT-4, I never found dirt or oil past the filter, and it never affected the MAF sensor. People complaining about oil on the sensor are delusional or doing it wrong, and K&N has released tons of test results that back that up. They even tested over-oiled filters.

If outback turbos are not working as well, heed people's warnings, but I wouldn't worry too much about it. On one of my older cars (a '92 Mazda) I had a monster flow foam filter and that worked fine as well.

Test it yourself. I never saw dirt or crap get through, and these arguments often dissolve into 3 simultaneous unproven "my buddy said/ I prefer/ my shop uses/refuses to use" arguments that are not based on a whole lot of fact. Buy one, pop it in, take it off road for a good distance. When you get back, pop the filter out and wipe a clean white paper towel. If it sucks, take it back and find something else. But vehicles with forced induction definitely benefit from less restriction in the intake and exhaust, which often requires tuning to get running well like Seabass mentioned. With newer vehicles it's no longer simply just drop in and forget it. But 90% of the time, friends cars that have problems with modifications are a result of not doing it right or half-assed installations.
 

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After being in the moto business and specializing in dual sport applications, we never recommended K&N's and would only "allow" their implementation on street only bikes. Why? Because they don't filter dirt for s***.
Lol, not strictly true, but for anyone with half a brain a low restriction performance filter is obviously that !, It's a dumb screen, it can not let more air through without more crap also.

If like everything, it is maintained, cleaned and oiled every 500 miles (in a dusty environment) it will do a reasonable job.
 
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