Has anyone tried K&N Engine Air Filters?

I'm changing the original filter next week, 15,000 miles. The parts store where I tried to get a Prius filter doesn't stock them -- the line was, "It's too new for us to stock them; you don't need a filter now for the '08." They stock K&N and Purolater, primarily. And, as I understand it, Walmart doesn't stock Prius air filters at all; at least, they weren't on the shelves.

Another parts store got a Wix filter it in within 3 hours of my order. My mechanic recommended Wix, so why not, eh? I haven't heard of that one, but we'll see.

 

As far as I know, the all the filters in the 2008 are identical to the 2007, so just tell them it's a 2007 if they give you a problem.

 

It doesn't matter. I don't like a business saying they don't stock an item because it is not necessary -- not their decision. If they had said there wasn't much call for the filter, I'd understand. But not this way...

 

Pls note that you can purchase the correct Toyota-brand engine air filter for $13, the cabin air filter for $15, and oil filters for ~$3.29 each (when buying a case of 10), from here:
Champion ToyotaWorld

Of course the shipping charge is extra, but if you buy a sufficient quantity to leverage the shipping charge then it makes sense to place a web order rather than buy locally.

 

Yeah, if I had a convenient place to store all that. When we built the house, we forgot to make sure of future storage. But I don't mind buying once at a time. Gives me a reason to get out and about. But the prices are in line with what I have been paying, seems like.

 

Although I sympathize with your problem, I offer this solution to both your filter and web problem.

K&N High Performance Air Filters, Oil Filters, & Air Intakes - Official K&N Engineering Site

The site includes many interesting pages of information.

 

You don't have any place to store 3 car filters? Thats a small house!
BTW, Wix filters are crap. Thats the stuff that Jiffy Lube uses. Go with Patrick's online recom. OEM is not that bad $$$$ and is the best. At least for our very tightly EPA car.

 

Folks can safely ignore this bit of nonsense. I used K&N's for 100,000's of thousands of miles on Japanese 4-bangers without problems.

What the poster describes is repeatedly OVER OILING THE FILTER and probably improper installation. It also sounds as if it was being done way too frequently (how many times was he doing this in 25,000 miles???) I was careful about oiling mine and setting it out on the bench for a few hours to distribute the filter oil, as well as wiping away any excess.

Yes, the K&N will reduce the differential across the filter as the path is less torturous. If you put in a K&N expect a little more horsepower (or "hose power" as stated above) at a given throttle opening. It is also likely to let through somewhat more fine particulate since that is part of the trade off, but over the life of my vehicles I never had any problem as a result. In fact, it improved throttle linearity in my 240 and my Accord (particularly the Accord where it widened the smooth acceleration sweet spot without getting into the VTEC operation.)

Chalk the poster's problems up to operator error.

 

I work on cars for a living. I do see a lot of K&N filters and most of them don't cause any problems. I have seen several contaminated MAF sensors from people over-oiling them. I have also seen studies showing a good paper filter catches smaller particles. If you put a lot of miles on your car then the limiting factor of the cars life may be engine wear, in which case you would want to use a paper filter. Most cars get old and deteriorate and get replaced for other reasons before the engine wears out.

 

For OBDII (OBDII is mandatory for all cars sold in the USA since 1996) cars in normal use, there is no case to be made for a K&N filter. Even granting that a K&N will allow less airflow restriction, one will not get getter gas mileage from it in an OBDII car as the fuel/air mixture is adjusted in a closed loop system so the car knows how much air it is gulping at any given moment. Consumer Reports used duct tape to progressively block an air filter in a car and found no difference in mileage (scroll down to the Change Your Air Filter paragraph).

For all but throttle wide open, the restriction is the throttle plate rather than the air filter, and the MAF sensor measure the amount of air flowing while the O2 sensors measure the state of the combustion with the fuel feed from the injectors adjusted accordingly.

The only case where a less restrictive air filter in a OBDII car might make a difference is at throttle wide open as the less restrictive flow might allow more air into the engine which might give one ever so slight more full throttle horse power. However, this is at the potential cost of lesser filtration and the possibility of oil from the filter fouling the MAF sensor.

Rumple

 

I agree that K&N filter will not increase horse power even if the air flow can be increased. The reason is the fuel injectors from the factory is sized for the max output of that engine. In order to get more max horse power, more fuel is needed and thus a higher flow rate injector.

I do use a K&N filter for a 87 Camry and experience no increase of performance of any kind. I used it to save money for reuse.

 

Right about mileage, wrong about horsepower as I've been pointing out, the case is simple: slightly more power when you demand it (high throttle openings.) Mileage won't improve because the efficiency isn't changing nor is the mix. Even before OBDII cars were using O2 sensors to adjust the fuel air mix. I've had K&N's on cars with O2 sensor loops and timed them 0-60 back to back with and without K&N cone filter set ups. It made a noticeable and measurable difference (0.4 seconds on the Accord and 0.5 seconds on the 240 if memory serves for multiple timed runs.) In both cases an air horn was used in place of the stock filter box so the effect was greater than a K&N in a stock box (which is still more restricted.)

Close, but not quite. The mechanism is correct but the throttle position for a given power output shifts. The K&N will be providing more air before WOT is reached so you get more power at less throttle opening (the throttle becomes more responsive.) But you will notice the power most at wider throttle openings because that is when you are actually seeking it. My Accord VTEC throttle response was tremendously improved by the K&N because it seemed to linearize the throttle in the mid throttle range (which was originally flat and stepped in feel) rather than having either a lugging feel or kicking it onto the VTEC cam setting because I had to keep adding throttle to get a response. It was an unexpected drivability benefit that my wife even noticed immediately (it was her daily driver.)

There is no "might allow" about it. It does. At a given throttle position less DP occurs at the filter allowing slightly more air to reach the throttle. At a given throttle position air flow is increased. A more restrictive filter is analagous to higher altitude since the air reaches the throttle body at a lower pressure.

Wrong. The injectors were also sized in the same basic manner on the other vehicles I've owned, but provided more power with more air. It's been along time since I studied the control on them but as I recall the control systems use the O2 to vary the duration of the pulse. These were mapped in the ECU for MAF or MAP system (depending on type--I tested on vehicles with both). There were various inputs.

IIRC where injectors get you is if you do enough upgrades that the max injector pulse can't match the air charge so that the system begins running too lean and you start getting detonation. That would take some pretty radical additional air (such as putting a turbo on an NA vehicle.) If I had put a mild turbo on my 240 I believe I would have needed larger injectors, but it has been a long time so I don't recall.

The point is the engine will make more power at WOT...assuming that the Prius doesn't actually limit the air flow by restricting the throttle opening or do something limiting with the Atkinson valve timing cycle. However, folks should not expect big changes, at least not with the stock air box and a drop-in K&N. The filter area already seems reasonable for the small displacement engine and its relatively low power output so the DP reduction is not likely to be great with a more free flowing filter. Still, if I was operating regularly at several thousand feet of altitude I would be inclined to use a K&N, because I might need WOT to compensate for reduced power (not to mention long grades.) We're talking about something like perhaps 2 horsepower, nothing big.

Nothing magical: 1. Don't expect better mileage from a K&N (or other reduced DP filter.) 2. Expect a small increment of additional power at high load because more air will be available for combustion. 3. Expect somewhat less efficient filtering of small particulates, but don't expect this to limit your engine life unless you routinely get 250,000+ miles out of your vehicles. 4. Expect to clean the K&N about as frequently as you would change the stock air filter. 5. If you over oil the filter you can foul the mass air flow (MAF) sensor.

 

We are talking direct filter replacement of the stock filter, not with a cold intake system replacing the stock air box. You elapse time improvement came from from less restrictive intake pipe rather than the filter.

Horse power output is directly proportional to the amount of fuel injected to the engine and amount of air that it can pump.

 

Thanks for sharing your thoughts and experiences Shawn, much appreciated and you have given me something to think about! Rumple.

 

Nope. It wasn't a "cold intake system". It was actually hotter than stock as the air was pulled from the engine bay rather than from around the grill. This was a drawback on hot days, but it still made more power than stock even then, just not as much as on cool days. This was a factor at idle, less so once the vehicle was moving. (I never did get around to building a cold air intake box as a result.) There was enough extra air coming into the throttle chamber that I could hear a restriction in the swirl control valves taking over around 6000 rpm in cool weather WOT. To get more power near redline I would have had to pull them--they were there to improve low rpm engine smoothness/efficiency and were open but not completely out of the way at higher rpm. When the weather was hot I could hear the restriction start at about 5000 rpm WOT.

The air horn set up was at the end of the intake pipe where the box used to sit, so the long runner to the throttle and throttle chamber was unchanged on the 240. Part of this pipe was replaced on the Accord, but the length was unchanged and the effective restriction of the pipe itself was negligible. Changing the shape of the opening from sharp edge to a venturi does reduce DP and allow more airflow, but it takes a reduction of the DP of the filter to make use of it. You have to look at this system wide and remove bottlenecks incrementally.

Replacement of the stock filter is still going to reduce DP and it will therefore produce more power. The change won't be as large. The only way this won't happen is if there is something specific to the Prius' unusual ICE throttle management system that would prevent it from drawing in the extra air. This is entirely possible and Patrick or someone else might know. I find it unlikely because if it did then the car would have a fixed amount of horsepower at various altitudes as well.

That air comes through the filter which limits how much air can enter with the throttle wide open. With the throttle wide open the air filter becomes the greatest restriction other than the valves/valve ports. Hence the comparison to operating at higher altitude. Fuel is added to get the proper stoichiometric ratio.

 

This theoretical discussion is not relevant to a Prius. The hotter the engine the better for Prius efficiency. Winter is a far worse mileage thief than any plugged filter. The problem becomes keeping enough heat around to raise the mileage and fuel efficiency. See the link.

[ http://techno-fandom.org/~hobbit/cars/warmair/ ]

 

rusty houndog,

Actually that would benefit from an under the hood intake as it would draw warm engine air in. But either way, more air should = more power. Keep in mind that all else being equal more power often equates to lower efficiency (mileage)...if one makes use of the additional power.

Optimizing for power/acceleration versus optimizing for efficiency are two very different (and most often opposing) tendencies.

The theoretical discussion is still relevant. The question is what the person installing a K&N is after. If they are after greater efficiency (mileage) they will likely be disappointed. If they expect large boosts to horsepower they will likely be disappointed. If instead they are looking for a small incremental increase in power at high throttle opening, or eliminating throwaway filfters then they should reap some benefits. Put enough small benefits together and you have something.

 

I wouldn't risk it.
I'll use the element Toyota use, the one that allows Toyota cars to cover huge mileage without wearing out.
If you want to experiment with lesser filters go ahead.

 

As Pat has already stated, do you see large industrial equipment, the kind that costs half a million bucks and up, running K&N, or the paper air filter element sold by Caterpillar, Cummins, Detroit, etc?

I have a tractor at my hobby farm that has an oil bath bowl and the main filter element. Seems to work fine

I have never noticed any difference in performance with plugged air filters, unless at WOT. Just driving around, no difference. Not all of us are flooring it at every green light

I'm completely against those cold air intake kits that scoop air from under the bumper. If you happen to try to drive through a flooded street, you could ingest water. There are tiny drain holes in the stock air box, but if you ingest enough water, forget about it

 

The FUD is getting downright silly.

If you want some extra power out of your Prius at times, a K&N is one way to get a small nudge. It won't work miracles and it's not going to destroy your engine.

If people applied this same skepticism to the Prius restarting the engine several times on each drive, the traction battery, or to engine block heaters, or grill blocking...it would be similarly silly.