I have a k&n panel filter on my dads 1.4 tdi ecomotive mk4 and before it used to have a range of 400miles whereas afterwards with careful Eco driving I could get the range to about 500 miles max and for my drive to work I could manage about 45-50mpg urban. I know this is all based on a diesel but just thought I'd give my input to show that with careful driving filters do work.