I used a K&N filter on my Boxster-S years ago and it fouled up my MAF mass airflow sensor because of the oil blowing down airstream onto the sensor. If you get one, let it dry out for a few days before installing it. You'll know what I mean if you get one. These filters allow more airflow but only significantly when at high RPM's for a bit better hoursepower perhaps. I would bet money that any mpg gain from just a filter change would be next to nothing.

On high performance engines with a poor design to start with or along with other intake, tuning changes they might be worth the cost/trouble.

I'm in the 12-14 mpg range, with a lot of local driving.

11.3mpg is a little on the thirsty side but not unreasonable. Much depends on your driving environment and driving style. With more milage on your vehicle the economy will improve. The OBC should be reasonably accurate but do a real-world check if you are concerned. I can't see that a K&N filter will help.

You bought a 2.5 ton vehicle w/ the biggest engine they make for the X, short of the X5M. What did you expect? I think your mistaken if you beleieve switching to a free flow filter is going to help increase your gas mileage, or at least measureably...it's marketing gimmicks on those commercials. They may flow more air, sure...but a mileage increase is kind of stretch...at least on a BMW. If you do anything, stay away from oil based filters, the oil wicks away and wrecks havoc on the MAF. Use either dry filter or maybe even a foam filter.

Have you tried just calculating the mileage yourself? The OBC fuel consumption can be adjusted, so maybe yours is just off a little. Also, are you ONLY using premium gas from a good gas station? That means none of the Costco, Citgo, etc crap. You need to be using Shell, Chevron, Texaco and 91+ octane or else the computer backs the timing off due to detonation and you actually lose gas mileage by using 87 or 89 octane.

I agree. Stay away from K+N, etc. IF it was so simple, why wouldn't the manufacturers make these filters standard.

I think I average 14-15 with mixed driving. Like someone said, its a big vehicle with a big V8. The mileage will suck