Okay, try this...
Take a piece of paper and try to breathe through it. DOH!@!! You can't, can you??!!!!
Now take a piece of cotton gauze like the ones used for cuts and big gaping motorcycle wounds, and try to breathe through that. Hey! Big difference!
This is how your engine makes power...get the most air in and out and you will make the most power that your combination will allow.
Now, i agree with the others that if your truck is a piece of Cow Poop, then slapping on a K&N will not do anything!! It will only waste your money and make you frustrated.
You most likely will not feel 7-15 horsepower on a newer truck that makes 250-350 horsepower. But its possible to do so. Theres many other factors that attribute to that "seat of the pants" feeling.
I run a K&N filter and noticed a difference when I switched to it.
And besides, motors are designed to work efficiently (or, most efficiently) at a certain RPM. You probably wont feel "the power" all through the vehicles powerband.
But...Using a K&N will save you money in the long run and will catch more dirt and crap in the air than a normal paper filter.
So if saving money isn't "performance" (more specifically : "pocketbook performance") than I don't know what is.
Travis Rydberg