Actually there is a benifit to a drop in....When a paper filter is new it flows its best but that also lets more dirt in..when it starts to get dirty the fibres clog and flow slows down messing with air/fuel ratio and maybe a lil mpg..A paper filter is a one deminisional way of filtering..
Now comes the multi deminisional type filter such as k&n which is a multi deminisional filter..When the front of the filter we will call it fills up you still have other sides(sorta speak)to keep the flow going..Think of it like a triangle,front clogs and you still have two sides flowing...Performance gain,i doubt anything a dyno would pick up...MPG well its possible but to hard to measure..
