WHAT IS IT? The pancake foam filter is not one of the best features of the 2010?2012 Yamaha YZ450Fs. K&N’s molded, rubber-framed, washable, reusable, YA-4510 fabric air filter tries to solve the YZ450F’s problems.

WHAT’S IT COST? $65.00.

CONTACT? or (800) 858-3333.

Here’s a list of things that stand out with K&N’s YZ450F air filter.

(1) Construction . A fabric filter is an entirely different animal from the typical foam air filter. Instead of oil-soaked reticulated foam membranes to trap dirt, a fabric filter uses fine strands of oil-soaked cotton material sandwiched between two layers of wire screen. To increase the filter’s surface area, the material is pleated. As with foam air filters, fabric filters depend on air-filter oil to trap the dirt. The structure of the fabric filter creates a counterintuitive phenomenon. Many dirt particles are trapped in such a way that they become part of the filter and help catch more dirt. This leads to the belief that, as a fabric air filter gets dirty, it works better than it did when it was clean.

(2) Installation.
The K&N filter is a straight swap-out for the stock foam filter. The only extra step is removing the inset backfire screen, which isn’t needed since the K&N has its own screen built in. There are no extra fasteners or parts to keep track of, and it’s very easy to switch back and forth between the stocker and the K&N. Out of the box, the K&N filter is pre-oiled, but the black polyurethane sealing surface needs to be greased to help it stay secure. We think the fit of the K&N could be tighter, but ultimately we were satisfied with the seal.

(3) Maintenance. The YZ-F’s foam filter gets dirty quickly and should be cleaned after every ride. Not a single MXA test rider looks forward to hacking into the YZ450F airbox, because it is a hassle. For those test riders, the K&N air filter is a blessing. Because it flows more air to begin with and seems to trap dirt better as it gets a little dirty, riders could skip cleaning it for a ride or two (depending on conditions).

(4) Learning curve.
It takes a little time to adjust to a fabric filter when you are accustomed to a foam system. Luckily, K&N supplies good instructions and offers a complete care kit?including grease, oil and cleaner?to make life easier.

(5) Performance . First and foremost, the K&N was louder than the stock filter. Because it sucks more air through its fabric design, test riders could hear the YZ450F’s obnoxious intake sound grow louder. Once in motion, test riders could feel a slight increase in throttle response, but in the seat-of-the-pants dyno tests, no rider raved about an overall increase in power. Although the MXA test riders’ educated derriŠres couldn’t feel a difference, the dyno could. The K&N air filter made a little more power everywhere on the curve (with the peak gain being 0.88 horsepower at 8000 rpm). The gain over stock tapers off after eight grand, but kicks in again on over-rev (producing 0.82 more power at 11,000). These numbers are nothing to sneeze at for a simple air-filter change.

We had three criticisms. (1) We never noticed any dirt infiltration around the rim of the filter, but if K&N were to develop a special cage that improved clamping pressure and fit, it would increase our peace of mind. (2) The K&N filter was markedly noisier. (3) Fabric filters are more delicate by nature and must be handled gently. Don’t squeeze, blast or toss the K&N around like a foam filter, or the cotton element will become displaced and cease to function properly.

For such a common motorcycle part, the K&N air filter produced a noticeable performance boost. Most test riders preferred the K&N fabric filter because it could go longer between cleanings.

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