K&N Cold Air Intake Kit: Increase Acceleration & Engine Growl, Guaranteed to Increase Horsepower up to 9HP: Compatible with 3.5L, V6, 2009-2012 FORD (Flex), 77-2578KS

Install took about a hour and overall was pretty simple to put in. Under normal throttle it sounds stock but when you put your foot down it makes that 3.5L sound like a beast it also has a nice whistle on vigorous acceleration. I also have a exhaust system on my Flex and it made it a little louder. It is awesome to see people's faces when you pass them and there is a sweet sound coming off the tail pipe. Will this turn your Flex into a race car? Absolutely not will it bring a giant smile to your face when you put your foot down? Of course it will !! This is a awesome product and I would recommend it.

Works great on my Flex and increased my avg MPG about 1.5-2 MPG

Oh hell yes this was worth the price.