Flat drop in won't get you that much, but I have run them on all my non-performance cars. Can get up to 1 mpg higher and it does seem to free up some low end, but hard to tell if there's any real hp gain.
Sorry to burst anyones bubble but, for a drop in filter you will not gain anything!.. It's been proven!.. Think about it and don't go for the hype!.. The opening to your air box is not any bigger, nor is the inlet tube leading to your intake manifold!... So in reality your not getting any more air into your engine!..