Just got a brand new 650i and want to know if it is worth it to get a k&N filter for it? What gains are there? Will i have to rejet for it?

 

Yes! I would say that a K&N filter is the best bang for your buck product out there. It will add performance not to mention you can simply clean it and re-oil it instead of buy a new OEM filter. You shouldn't have to re-jet it, however if you remove the airbox lid then you probably will have to.

 

I say do a search on the forums for K&N then decide for yourself.
They may flow a little better than a Uni or a Twin Air and quite a bit better than stock but lots of people have had problems with them passing too much dirt. I know I for one will never run another K&N for offroad applications.

 

I have a K&N and have no problems. I carry my stock filter incase it gets real dusty. Its worth it.

 

I gotta agree with this assessment. The reason a filter will flow more air is related to surface area and porosity. IMO the K&N is great a flowing air but mediocre at removing dirt from the intake air.

 

I wouldnt expect much gain from any aftermarket filter.I've tried different filters but just cant seem to tell any difference.Need to do some more mods before you'll tell any difference.

 

IMO the oil is to thin, I had one on my Griz. and the heat from the engine would make the oil run right out of the filter and it would puddle up in the bottum of the air box, I now use a UNI, the oil for the foam filters is a lot thicker and stickier, plus the foam filters like UNI and Twin-Air are about $30 cheaper, and are just as good or better than the K&N.

 

It's called a "PRE-FILTER" gentlemen. Use one and quit complaining about it allowing too much dirt into your engine. Personally, I don't really care what kind of air filter you run, and neither should the guy riding beside you. It's your choice, and it's your machine. The K&N with a pre filter works just as well if not better than any of the other filters. The foam filters work great also, w/o having to use a pre-filter. People make it sound like the K&N is worthless compared to other makes and brands of foam filters. K&N has been around for a LONG *** time. A lot longer than a lot of other manufacturers. On the other hand, there is nothing wrong with the airfilter your bike came with either. Clean it, oil it and run it. As far a looking for a filter for a performance upgrade, I would rather you spend your hard earned money on something where you will actually see a different, not just think there is one. There is a reason, or should a say a couple of reasons your bike came with the filter it did. The first reason is obviouly because it's cheap!!! The second reason being that it obviously works for its intended purpose. Think about it.

 

I love my K&N filters, I have never had a problem,
Any filter will allow dust into an engine. It just varies on how much air enters into it.
As far as the oil being to thin to trap the particles, bullcrap, Just oil it more and let it drip off for a few minutes. Most of the damage being done to an engine because of "dust" not being filtered out enough is barely noticible, I just rebuilt my 87 moto 4 80cc after god knows how many miles, (running just the stock foam air filter) The intake valve was beat into the head, the dust coming through the engine causes the soft valve to grind itself down and as it beats against the harder metal of the head it wears away, if I had a K&N it might have another year, if I had a UNI or a Twin air, who knows maybe another year or two, either way, who cares, pick whatever you feel comfortable with, a foam UNI is not really any better than the foam factory filter.......JMO