I would say that you should have to retune, but you most likely have to adjust your tune each time you run (if you're running a proper tune) so it shouldn't be any different. What I'm trying to say is if I run my RC today, even though I adjust the tune throughout the day with changing weather, when I go out tomorrow, I'm definitely going to need to retune. So with or without the filter I'm going to adjust the tune, so it shouldn't matter much.