Panel Filter change of heart!
Stuck in a panel filter to my 146 boxer yesterday and had a moan about it as it didn't feel any different.
I take that back. This morning something changed - I think it actually has made a difference - it always sounds nice and raspy but it somehow has sort of thickened up! Holding onto the revs for as long as possible as usual and it sort of gives it a bit more kick - not a lot - but its there - and the sound is, well, even more raspy.
Like everyone says, it won't give any more BHP, but just gives it a tiny bit of extra growl and a bit more balls.