Cold Air Intakes replace the factory air intake box and paper filter with a system that allows more air, colder (denser) air to enter the engine. K&N®'s Air Charger® uses a cleanable, reusable cone filter that does not need replacement.  

Because Cold Air Intakes allow more, colder air into the engine, a Cold Air Intake will allow the engine to make more power than with the stock air intake.  This gives you better horsepower, better torque, better acceleration, and better fuel efficiency (miles per gallon) depending on how you drive your car.  When I last researched K&N's web site, their product description stated that at 5222 RPM, an LS4 will put out roughly 13.48 more horsepower than an otherwise stock LS4.

I've had a K&N Cold Air Intake on my Impala since 2007.  The car sounds better, the fuel efficiency is improved, and I noticed the increased horsepower immediately.  This was a very easy modification to perform and only required a few simple hand tools.