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bkoz

'10+ Best Air Filter System

6 posts in this topic

What is the best air filter system for the 2010 and up YZ450F.

A K'n'N came with the bike and I am not impressed. It doesn't seal well (needs grease) and it kind of floats on the sealing surfaced because it fits loosely. I also had the filter clip pop off and have to use a zip tie to hold it in place.

I don't care about added throttle response or anything like that. The bike doesn't need it.

I am looking for the best way to keep dirt out of the engine because the K'n'N is not cutting it.

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I honestly think the stock filter and back screen work fine. Everyone talks about gaining airbox volume on street bikes, and everyone seems to talk about gaining filter surface on dirt bikes.

I'm not sure if the bikes needs tons more air period, but if it does I don't seem like surface area on the filter makes much difference if you can't get the air into the box. Based on that, I'm not sure that the TwinAir, DT1, etc. do much if anything.

I also feel like as more and more newer fuel injected bikes come out (2013 CRF), you'll see the air boxes get smaller based purely on available space. My guess is HP numbers "mysteriously" don't go down.

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When considering this question, you have to understand that there are two primary issues involved. The most important is adequate filtration. The two types of elements generally available, foam and gauze (think K&N) both depend on being properly cleaned and even more so on being properly and completely oiled in order to filter much of anything finer than coarse sand, so the choice of oil is very important. Gauze filters actually filter better than foam...at first. The trouble is that they are so thin that the media quickly reaches its full capacity for holding fine dust, and after that, they either obstruct air flow or allow dirt to pass, or both. Foam elements are much deeper, and as the outermost parts of the surface become completely coated so that the oil can't hold any more, dirt travels deeper into the foam, where, if it was oiled right, it gets stuck on the oiled foam there.

The second thing is the performance issue. When thinking about this, the question is "where is the bottleneck, and is it really a restriction on the engine?" Increasing the filter area is always beneficial to an off road engine because even if the filter is already big enough not to be restrictive, a bigger element will improve filtration in two ways. First, it obviously has more dirt holding capacity due to its larger size, and second, the larger the filter area, the slower air will flow through the media. The slower the air flow through a filter, the more likely it is to be able to trap and hold dirt.

The volume within an air box should be as large as practical, again for the same two reasons. In a roomier air box, the air moves more slowly around the filter, which creates an opportunity for dirt to simply fall out of the air altogether. From a performance standpoint, what you are trying to create is a mass of "still" air around the intake horn that the engine can "see" as being open air. Air boxes, filters, and air boots are usually designed as a complete system, and if you look inside the air boot of a modern 4-stroke, you will usually see a bell shaped extension coming off the carb or throttle body that looks like an old school "velocity stack", the end of which stands a bit away from the sides of the boot. This is the tuned end of the intake tract, and the stiller the air can be made at that point, the better for power. So, the air volume under the filter in the boot is important as well.

The air path leading into the air box needs to be larger in total area to exceed the cross section of the throttle bore. If it is bigger than that, it will not pose a restriction on the engine. If the total air path area is smaller than that, there will be a depression, or a lowering of air pressure inside the air box compared with atmospheric pressure. However, once the entrance to the air box is even 10% larger than the throttle bore and there are no significant flow restrictions through the path, enlarging the entry ports, adding ports, or even cutting out the sides of the box won't improve anything.

IMO, you can spend a lot of money on filter and air box "improvements" that don't do anything outside of generate more noise, and the gains you get from a lot of them are purely imaginary. But I will tell you this: In '98-'09 YZF's, the filter element, big as it is, is the restrictive component of the intake system. That's why removing the flame screen has no effect on performance; it's not as restrictive as the filter is. Knowing that, the filter on the '10+ looks pretty small, and the first inclination I would have would be to increase the filter area to the greatest practical extent. But the snag is that with the new bike, simply installing a taller element will put the top of the filter right against the roof of the air box, more or less neutralizing the gain in area. With all that in mind, the Twin-Air kit that uses a new lower air box and a long filter element looks like the best setup. It's probably also nearly the most expensive solution, though

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I am not really interested in performance gains. The 450 has more than enough power to keep me entertained.

And I disagree that gauze filters filter better than foam. My past experiences have shown that very fine dust will get past the gauze filter when it is freshly oiled. I do not get this with foam filters.

Can anybody comment on how the Twin Air Powerflow setup is to clean. It looks like dirt can be easily knocked into the air boot.

Note that the bike did not come with the stock filter so I have no idea what it is like maintenance wise.

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The twin Air Powerflow is IMHO easier to clean than the stock setup or the modified stock setups.

When I take the filter off, all the dirt and grime stay attached to the filter and as long as I don't knock it on something, no issues. It doesn't warp or wobble because of the steel cage it is over. It "could" be a problem if you are the type that goes 4-5 rides in loamy dirt between cleanings. I change my filter every ride day. The filter has so much surface area that even after 1 day in some of the worst conditions, only 1/4 of the filter is visibly soiled. I have never seen even a speck of dirt at the bottom of the airbox after removing the cage. It would be easy to see on the orange background.

One downside to the powerflow box is that the "cnc machined" cap doesn't fit after about 3-4 washings. Oils must make the rubber boot that goes from the airbox to the engine swell somewhat. What I do is put 2 paper towels into the opening and then the wash cap on during bike washing. After I have dried the bike off, i take the paper towels out and just replace with the cap. I use the moist paper towels to clean any residual oil in the airbox. I wash the filter box every time I wash my bike(after every ride day)

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I am not really interested in performance gains. The 450 has more than enough power to keep me entertained.

And I disagree that gauze filters filter better than foam. My past experiences have shown that very fine dust will get past the gauze filter when it is freshly oiled. I do not get this with foam filters.

I mention power improvements because there is a common obsession with the idea that the air intakes leading into the shrouds on the new bike are too small (they aren't) and that there is "free" horsepower to be gained by punching holes in the shrouds.

You can disagree on gauze filters if you like, and I am not a fan of them at all, but the fact is that when they are correctly prepped they do, at the very first, filter better than foam. There are some variable involved, such as air velocity across the media, but lab test measurements do support that. From a practical standpoint, however, this advantage does not last long enough to be useful, and the reality is that in any dusty environment, you'd have to swap in a fresh element at least once a ride day to match the filtering performance of a good foam filter with an aggressive oil worked through it.

The main reason I even bother to point this out at all is because the companies that offer gauze elements tend to make the claim that they filter better. This is simply to explain the foundation for that claim. In real terms, it doesn't mean much, and I wouldn't consider using one.

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