K&N intake air system

If you're thinking of using it on a diesel the answer is never use a k&n. It will dust your turbo and intake. Google it, no one recommends it. And no, It may free up some horsepower from a restricted air flow. My air filter stock is good up to 500hp. There are better ways to spend your money for hp. I'd start with making sure your wheels are properly aligned and aired up, that will help.