Preacher

I bought the K&N, drop-in OEM-type oiled element.
Before opening the box,I'd like some informed opinions as
to wether this is a good idea.
If not,it's easily returned.

Thanks!

Gord96BRG

It depends what you want it for!

In the stock airbox, it will make absolutely NO difference in power.

If you want something that you can clean and re-oil to avoid having to buy replacement paper filters ever again, then it's good.

If you don't mind that it filters less efficiently (ie lets more small dirt particles through) than a paper filter, then by all means use it.

For me, personally - I don't see the point of less efficient filtration for no power benefit. I'd like my engine to last as long as possible, and the best filtration I can get will help that cause. Paper filters provide better filtration than K&N, so I'm sticking with the OEM paper filters.

Regards,
Gordon

tpryor

Here's what I know for CERTAIN - I had one installed in my car for about three weeks.

My gas mileage and throttle response improved IMMEDIATELY (from 16 avg to 18 avg) on the street.

It seemed like it did NOT want to idle (but it always did).

The mass airflow sensor will need to be cleaned (GOOD cleaner spray - no solvent, evaporates fully) about once a month. The little sensors (waaayyy up in the top of the fixture) get a little oily. Cleaning only takes a couple of minutes.

Do NOT try to autocross with one! This is ultimately why I removed it. The car initially accelerates well, but when you come out of the throttle, and then back on hard, the engine stumbles badly for a second, then seems like it's REALLY struggling to make power.

Given a second to "recover" the car is fine.

If I were only driving it on the street, I would have left it in, but I have the second biggest event of the year coming up this weekend, so out it came.

If you want any further details, feel free to PM me.

rotarygod

I don't know where the misinformation came from and keeps coming from about K&N style filters. They are superior to paper in flow. They have not been proven worse in tests. They filter just as good as a paper filter and even when clogged they still out flow a clean paper filter. I need to find the filter test from the Supra forum to post on here. If you intend to keep the stock airbox it is a good thing to have as long as you do not over oil it. You will not feel an increase in power just from feel though. You won't feel a gain from a cone setup either. This doesn't mean that each system can't get power improvements. They just aren't enough to feel on their own.

Preacher

oily sensors....no thanks....I'll just do something different when I've researched a bit more....I'm a neat freak,no need to gum up sensitive parts with oil....and I have the K&N FIMK on my 4-runner,I never thought about oily intake sensors before....hmmm....

Gord96BRG

From other tests and analysis that have been posted in various car forums over the past 9 years that I've been online?

Quote:

They are superior to paper in flow. They have not been proven worse in tests.

Nobody disputes that they flow better than paper filters. However, in a stock intake system, especially one like the RX-8 with a very large filter element, the filter is NOT a restriction, and you could run with no filter at all and make no extra power. Therefore, it's irrelevent whether a K&N flows better than a paper filter, because the engine will make exactly the same power with either. So why use the K&N?

Quote:

They filter just as good as a paper filter and even when clogged they still out flow a clean paper filter. I need to find the filter test from the Supra forum to post on here.

This is the dispute - I've seen many tests and studies that prove that they do NOT filter just as good as paper, especially when clean. Maybe when clogged with dirt they filter as well as paper, but it's been proven over and over that they let more fine particulates through than paper filters. Check out www.bobistheoilguy.com for one such comparative study.

So - no extra power to be had, less effective filtering. No thanks!

Regards,
Gordon

rotarygod

If you completely remove the filter from the stock RX-8 intake, you will see about a 4 hp peak gain. This assumes it isn't on the 1% or so of RX-8s that actually runs better with the filter installed.

I do agree that there is no feelable difference from ANY intake change.

They do filter better though. If they didn't, they wouldn't be the filter of choice among baja racers. Those guys absolutely need a good filter.

Gord96BRG

For how long?? Filtering requirements of racers (even desert racers) are significantly different than long-life street cars. For racers, low restriction and not clogging up to the point of blocking airflow completely are paramount. Filtering all the small particulates are not important to them at all - they don't care if their engines last 150K miles, only if they last 1K miles (or 5K miles for a season, whatever).

My requirements for an air filter for a street car are definitely not the same as those of a desert racer, so I would not presume that their choices are automatically the best choices for me.

Regards,
Gordon

Preacher

It was easily returned this afternoon,and until MazdaSpeed makes an improved filter,the stock one (which I was very impressed with the build-qual of) will be staying.

Thanks,all!

rotarygod

That was an extremely predicatable response. K&N's element is not the same as many of the look alikes out there. Some don't filter well. K&N's do though. Apexi makes the best flowing and filtering one out there with the K&N a close second. The nonoiled foam elements such as those from HKS, filter and flow bad. Filtering ability does not necessarily correlate with flow rate which is why a paper filter does not necessarily filter better even tough it flows less. It doesn't.

Nubo

I had a K&N filter on my Miata for most of its 150,000 miles. My perceptions

1 - no discernable difference in performance (of course they only claimed a couple hp anyway)

2 - washing and re-oiling is not more convenient than dropping in a new element. But, once you have the stuff you might as well use it...

3 - I was always worried because when you hold up the K&N there are some seriously large "holes" in the medium that you can really see daylight through.

4 - seemed to do the job for 150,000 miles.

I'll probably stick with the stock element with the RX8 unless I start to discover the "oil in the airbox" issue in which case I might as well use a filter designed to be oily...

durrada

Here's my two cents... and that is probably about all it is worth

My perspective on this comes from motorcycle racing, so it may not have as much bearing here.

1. Racers probably care more than non-racers about engine life and longevity. Well, at least those of us who are privateers do. Parts are expensive ! If a filter is letting bad stuff through, I don't want to use it and almost all of us use K&N filters.

2. The hp increase on a bike is not very discernable on a motorcycle either until you change the jetting or the injection maps. This actually brings up a question for me. When you place a K&N filter on a bike you almost always change the jetting and ignition maps, does this not hold true for cars as well. I would think that a high rpm engine like the RX8 would have more similar needs to a high rpm motorcycle, but that's just me.

3. The most important thing for me with a K&N was that it cleaned the air better and allowed the engine to breath better (which can translate to lower temperatures). The more oxygen the better.

Anyhoo, that's just me. None of this has probably helped at all, but typing is so much fun - NOT.

Gord96BRG

Did you even read the filter test at the page I linked to? Here's the direct link to it . The conclusions directly contradict what you claim - their study, at least, proved that paper filters DID filter better. So what was wrong with their test, if you please? (I've seen other tests and studies that came to similar conclusions, but let's discuss this one for now...)

Regards,
Gordon

Nubo

I reviewed the filtration section of that test and I'd have to say the the method was not quite scientific. Each test relied on air intake from actual road driving which of course can vary widely and has no control over the type and/or amount of dust and particulates encountered. A few minutes following a diesel bus might do more "darkening" of the test media than the rest of the driving.

A real test of filtration would involve measured samples of particulate of various sizes in a given volume of air and then a quantitative analysis of the amount and type of particulates that escaped filtration. It would need to be in conjunction with information about which sizes of particles are actually damaging to an operating engine.

shawnio

http://mkiv.com/techarticles/filters_test/2/

That's the test that was done on supraforums that rotarygod was talking about.

mlino01

I and a couple other members are using the Green cotton wove filter. Great build quality and not over oiled from the factory. My 8 idles and runs great with not a hicup.

Gord96BRG

Hmmm - that test doesn't even compare a paper filter to an aftermarket filter element, and it seems from that report that the Skyline airbox was restrictive, which is why those aftermarket intake kits could all make 13+ hp (ie, it wasn't the filter giving the extra power by itself).

Sorry, I can't see how that test has anything at all that's relevant to an OEM paper vs. K&N drop-in replacement discussion!

Regards,
Gordon

JimW

Any statisitcs on the green filter? I might get it just so I dont have to open that damn airbox again!

ScudRunner

I myself am running the air filter that Racing Beat sells on their website. I just put it in last night. Will report any problems.

rotarygod

The element doesn't come that way. That is the result of not being careful enough when you are cleaning it. I once used an air compressor to blow out the filter (which they tell you not to do). Mine did the same thng. I had to buy a new one. No more problems and no more holes.