I Want The Truth With K&n Filters

[Timewerx]

I've been hearing a lot of things regarding K&N filters(mixed opinions). I've also been looking to installing one (OEM types that fits in the factory air filter box) until I could find a good reason to install one.

The thing that most concerns me is filtration quality. I've heard a lot of 'complaints' with K&N filters having inferior filtration quality than stock paper filters. I've even read independent tests showing K&N's inferior filtration quality to paper. So what is the truth?

What K&N claim about their filters is very attractive - lifetime guarantee, reusability, higher airflow. But if filtration quality will be worse than stock paper filter, then I'll just stick with stock paper filters! I'm a lot more concerned with engine longevity vs a care free, high flow air filter

[bothwell_buyer]

Simply, if you are happy with the car as it is, then don't go changing things.

K&N filters are very common and if they were not good for the car then I guess people would not buy them.

[Timewerx]

Simply, if you are happy with the car as it is, then don't go changing things.

K&N filters are very common and if they were not good for the car then I guess people would not buy them.

Very good answer. Many of the complaints I've read came from users who perform either top overhauls or just simply cleaning throttle body and have noticed the increased dirt buildup if using anything other than stock paper filters.

[Cyker]

TBH, it's just physics - With all things being equal, Higher airflow = less filtration. No way around it unless you change other factors, e.g. bigger airbox for bigger filter area.

The only real issues I've heard with K&N filters is that the oil they use can get sucked off and foul the MAF sensors, but I'm not sure if this is a problem with just-bought filters (bad), or where the owner put too much oil on after cleaning it (user error).

If you had one in long enough, the dirt build-up would act as additional filtering anyway so assuming the oil problem isn't bad it'd be okay.

TBH, after discovering what the EGR does, I've become less worried about how well the air filter works since the EGR is just dumping far worse quality air into the engine anyway!!! (I still can't believe what a stupid idea the EGR is...)

As long as it keeps wasps and such out of the engine it should be ok :)

I was thinking about getting one too, but they don't seem to make them for diesel Yarisseses?!

[Timewerx]

I agree with the physics.

I would guess that getting high flow (less filtration) filters is only worthwhile if you're spending time on the track and needed every little bit of performance and reliability would come second, then that would make sense.

[Cyker]

One (small) benefit is higher air-flow = easier air-flow and this is probably worth a (small) increase in mpg ;)

If they had ones for my D4D I'd try one just for comparison although I doubt it would make a significant difference. Higher filtration means nothing if you've got a stupid valve which dumps acidic sooty air from the exhaust back into the cylinder!