Will a K&N or other free-flow filter in the stock air box, with no other mods, help anything at all, such as mileage, power, etc, even if only a little, or would it be a waste of money?

You get a nice little decal to stick on your airbox.

I did it, but that was many, mant mods ago. Guess it was a starting point. Next came the $20 Lowe's CAI.

K&N in Stock Air Box 317hp
paper filter 315hp

NO filter 314hp and holding top part of the box UP (I guess too much air turbulence)

Thanks, Monaro; I feel a whole lot better about my $43 investment.

You will also get an additional 1-2 mpg with the K&N, but since they do not filter as well as paper element your oil will contain more dirt leading to shorter oil life. No big deal. Just have to change the oil sooner.

You will also get an additional 1-2 mpg with the K&N, but since they do not filter as well as paper element your oil will contain more dirt leading to shorter oil life. No big deal. Just have to change the oil sooner.
Where did you hear that? I don't think there is any real info that they don't filter as well. There is a lot of R/D in the K/N filters.

I'm definitely not knocking K&N filters as I have one on my G8 GXP with a yella terra tube. With that being said I did read an article in popular mechanics some time ago and remember they did run a test between a paper filter and a k&n.
The paper filter is made of compressed paper fibers and has a "pore"like property which means as it filters dirt and the pores become clogged it will not allow air through that exact pore in the filter, the air will have to find another open pore in the filter. Where the K&N filters the dirt and the cotton gauze still allows air flow through the filter but it supposedly allows small microns of dirt that are attached to the incoming air to be ingested into the engine.
This is why the K&N will still flow very efficient at 5,000 miles while the paper filter is very inefficient due to most of the pores being clogged up.
So in actuallity, the K&n will pick up more than 2hp in time as the paper element filter becomes clogged with dirt.

To sum it all up, Brand new paper filter and K&N will have very close flow numbers when new. As well as have very close filtration rates, but as miles rack up the paper filter becomes clogged and less air is allowed in, but still maintains the same filtration rate while the K&N still allows for alot of airflow but begins to lose it's filtration rate. I've never had a problem with K&N filters and will always use them.
I'm sure there's alot of guys/gals on the board who know more information on the subject than I am posting so please chime in.

The K&N will flow slightly better which in turn leans out the A/F ratio. That is where you get the extra 1-2 hp.

Personally I think the stock filter box is fine, what's limiting it is the size of the snorkel and also its placement. After removing it to see exactly where the snorkel was drawing in air, I was surprised that it could even pull air effectively from that place. I believe that cutting a hole in the lower guard and then using a tube to run from the cutout to the box will yield better results.

Actually K/N filters filter better when they get a little dirty, this is why they tell you not to clean them to often. They say people have problems when they clean them to often or over oil them. K/N also will will back you up if the dealer tries to blame the filter, for like MAF problems.

Personally I think the stock filter box is fine, what's limiting it is the size of the snorkel and also its placement. After removing it to see exactly where the snorkel was drawing in air, I was surprised that it could even pull air effectively from that place. I believe that cutting a hole in the lower guard and then using a tube to run from the cutout to the box will yield better results.

Just did that to my GXP, cut 4 inch hole where snorkle fits in airbox and glassed in a short 4inch alum tube and connected it to a hole in Splash pan with 4 inch flexible hose, also used Yella Terra intake tube.
Didn't seem to be any more intake noise even at wot. Of course I can't tell about performance.

Good free breathing, cold air mod for mininum expense, well except for yella terra,
those things aren't cheap, plus you can add a K&N if you want.

Personally I think the stock filter box is fine, what's limiting it is the size of the snorkel and also its placement. After removing it to see exactly where the snorkel was drawing in air, I was surprised that it could even pull air effectively from that place. I believe that cutting a hole in the lower guard and then using a tube to run from the cutout to the box will yield better results.


+1, i did the same thing. Dropin k&n, removed snorkle, and drilled holes in my lower honeycomb panel. Next will be a new intake tube from throttle body to airbox. I think ill go with 4" pvc with rubber boots. Ill paint the pvc to blend in better.