I recently replaced the stock air intake with an aftermarket (S&B, was disappointed in the quality of the plastic) and noticed a instant difference in the computed fuel mileage. I don't pay much attention to the computer calculated mileage on the overhead and can't remember when I last reset it, but after I installed the new intake, I took a look at it and it was reading 21. 1. Over the next 2 days I watched it slowly come up to 21. 4, this was with it trying to overcome the average for the previous ? months. So I reset the display and just running back and forth to work and around town for a few days it is at 24. 2. Not very scientific or accurate necessarily but still an indication of an definite increase. Sure there is a whistle too, but just keep the stereo on!