hey guys, the K&N air filter and the squar filter that replaces the top of the air box, is it worth getting? any noticeable power gains? does that top filter that replaces the top of the stock filter box keep out water? or is it a disaster waiting to happen.
My z400 is one of the EFI models "2013" iv heard that when doing mods you need to rejet the carb to get the HP gains but would the efi just readjust it self as needed? also I was thinking of getting a slip on muffler like a HMF or Yoshi. would any other mods be needed to acomadate the exhaust and or filter?

 

If you mostly ride at a track, that filter setup is fine. I, however, prefer the Uni foam filters and a stock lid. They may not have as much air flow as the K&N, but they filter better if you are riding in really dusty conditions. You need to look into purchasing a fuel programmer. Modern ATVs come really lean from the factory due to EPA regulations. When you modify your quad by allowing it to breath better, you need to richen you air/fuel mixture. You might as well get a complete exhaust system. There is probably no noticeable improvement with just a slip on.

 

I agree with nachop. I recommend foam filters for everything but dune/sand riding. The outerwear style airbox covers can be ok. They actually can be better than some stock covers in many instances. The efi in atvs is not a closed loop system stock. They will not adjust automatically to changes such as inhtake and exhaust as they have no O2 sensors. You will need an efi tuner if making any serious changes. A new filter and exhaust would dictate a tuner as well.

 

Unless your motor is modified, there is no increase in air flow.
Like mentioned, Foam is best and adding a foam pre-filter is good.
I ran a K&N for TT racing only. And never w/o a outerwears.

"I recommend foam filters for everything but dune/sand riding"
You'll never see me in sand with a K&N.
They say the fine dust from a track will go thru any filter. I believe the same about sand.
No offence Scooter.

IMO: forget about filters, get a set of shocks (PEP of course) so you can handle the speed you have now.

 

Have been running K&N filters with an outerwear of some type on ever quad that I've raced and ridden for the past 20+ years with no problems in just about every type of weather condition that you could encounter. IMO they offer as much protection with an airbox that you'll ever need unless your going to submerge your quad in a lake.

An outerwear does an excellent job of repelling sand, dust, dirt, mud, water and everything else that you'll encounter without sacrificing performance while a cloth filter like a K&N offers very good airflow and filtering depending on the ply that you get. The best way to compare/explain foam, cloth and paper filters is to get a piece of each material and expose them to the elements and see how they react. The simplest example is water. When you expose foam and cloth to water they both absorb it and expand reducing the ability to let air pass through while paper material breaks down. An outerwear greatly reduces this by repelling the water.

Here's an example of a 9 year old outerwear that I have repelling water and how well it works.

 

No offense taken LT80. The few times I have ridden in sand, I have used foam filters cause that is all I own. The problem is they clog quickly and are a bear to clean. That is at least the case with the YFZ that has an opening right at the lid for intake. Something with a snorkel may be more forgiving. This is where the K & N or outerwear style lid is better. That and sand tends to be mostly large enough particles for the K&N to handle.

 

The FCI setup that I run on my YFZ450 with no airbox has performed well in conditions that have included sand, rain, mud, dust and clay. The K&N & outerwear that I run on my Polaris Sport have also performed flawless in the same conditions. I do clean them after every race/ride and find that the outerwear really helps to protect the airfilter.

During dyno and track testing I've found that I make more power with a cloth type filter like a K&N and outerwear than I made with just a foam filter like a UNI. If you're worried about a standard cloth filter like K&N sells not offering enough protection you can buy one with more ply and it won't hurt your performance that I've seen. I run a standard K&N on both my Polaris quads and an upgraded ply cloth filter on my YFZ450. I even use a K&N and outerwear on an old Mustang that I own.

Don't get me wrong, there's nothing wrong with a foam UNI filter and they perform fine. I've just found that a K&N with an outerwear does the job just as well and makes more power at the same time. The only downside to a K&N/outerwear combination is they cost more than a UNI. If you really want to get the most out of an aftermarket airfilter look into something like an FCI setup to improve on your air intake velocity