I recently put the original factory air filter back into my 5.4 V8 F-250. I got better MPG with the factory filter than with the K&N. Does this make sense? Anyone else notice better or worse MPG with the K&N?

 

I went from 12.0 with stock setup
to 12.5 mpg with the kn fipk setup
but it does have a slight whistle sound to it
thats the only draw back
01 with 5.4

 

I put a filter element in my '01 5.4L at about 500 miles so I don't know the diffence for your setup but I did add a K&N FIPK at 35k miles and I picked up 1.5 mpg and the awesome intake sound you get with an open air filter.

 

I ran the K&N for about 14 days than went back to stock filter..... I wasnt impressed by any performance gains, and the filtration is not as high as the paper so why run it?..V10

 

did nothing for my truck
would return it but I threw the box away

 

I too purchased the K&N filter setup with no noticeable improvement. I noticed also that it doesn't seal very well with the hood like it's supposed to do. I would go for the sealed plastic box setup you can get to close off all engine compartment air and just feed it cooler outside air. I'm going to fashion stainless steel sides for it ( The mig welder needs dusting off) to close off the hot air. $250 is a lot to pay for no gains in my opinion.

 

Depends on which you're talking about....
The drop in filter didn't seem to do a thing for my cars... and there have been reports of 'dusting' of turbos because the K&N let's more than just more air thru the filter....

BUT,
I can personally praise the K&N Filter Injection Performance Kit !
I had a Jeep 5.9 Limited - it was NICE! - and after it turned 100k miles and the warranty had run out... I thought I'd try one of the FIPK's for it.... ad's said +25 HP....

After 100K miles you somewhat KNOW what your vehicle will do... so I knew the change to the FIPK gave the truck a HUGE kick in the pants !!! AND improved the fuel milage...

As far as if it would let in too much dust - don't know - but it sure made it a NEW vehicle after 100k miles !!! and ran well until 125K when I sold it...

I pulled the FIPK kit with the idea of letting someone else have fun with it... but haven't found anyone with the same motor to use it...