MX XStream Filter
K&N filters have been around for what seems like forever, and they are still here, just new and improved. The XStream Top Filter makes use of new technology to encase the cotton and screened filter media into the shapes and forms necessary to fit into current dirt bike applications. They are typically two-piece designs with a roundish outer part and a top cover piece that fit together snugly. The latest revision to the filter has been the new sealing lip between the two parts of the filter for a more secure seal, something that is vitally important with the cost of passing dirt on today’s high-performance engines. K&Ns have always claimed having more surface area available than conventional foam air filters, which makes sense due to the zigzagged pleats of the media. Also, since the filter acts as a cage and a screen, there is no need to remove the backfire screen in the stock cage, which for some created performance gains. The K&N design no longer uses the stock cage, so this is not a factor. But in most of our experience with the filter, clean stock to clean K&N, there was barely, if any, noticeable difference in power when riding. Where most riders did feel a difference was in throttle response or pickup from zero throttle. For almost every bike we have tried a K&N on the off-idle response gets better.We’ve never passed dirt through the filter material in a K&N, even fine silt. But we have had dirt seep past the filter-to-the-airbox sealing lip when the filter was improperly installed. This is an error on the installer for sure, but the harder rubber material is not as forgiving as foam along this seal if things are not perfect. A thin coat of grease goes a long way on increasing the effectiveness of the sealing lip on the K&N. This was mostly an issue on bikes with tight confines inside the airbox where it was difficult to check for proper alignment, early CRF four-strokes come to mind. Yet you can leave the top off the K&N and squeeze the tubular section of the filter easily past the frame rails or airbox opening and then check the alignment through the inside of the filter before installing the top.
But the rest of the K&N experience is wonderful as far as air filters go. Cleaning, with K&N’s cleaner is simple and less messy than with foam, and it is easy to see when you have all the dirt removed. The filters dry out easier, especially with mild compressed air being blown backward through the medium, plus oiling is easy as well. In fact, the K&N seems to use quite a bit less oil once you learn the right amount. Here is where the K&N comes into its own. The filter is the toughest filter we have ever used. It does not degrade, get torn, have glue issues or care too much about how long it has been left in the bike. And if left in the bike for a long time, getting dirtier and dirtier, the filter seems to let the bike run properly, meaning getting enough air, for longer than a foam filter will. About the only issue on the totally dirty side is that the K&N will completely plug, almost instantaneously, when run in very silty conditions, whereas a foam filter will keep allowing a small amount of air through (and foam will likely pass dirt before actually plugging in my experience). In an emergency you can remove the K&N, knock the dirt off, reinstall and keep going, in a race, for instance (I’ve done this in Baja).Retailing between $89 and $109, this could be the last filter you’d need to buy for your bike. I wouldn’t buy it based on performance, I’d buy it because it lasts. -Jimmy Lewis