CAI.........cold air intakes depending on their dimensions should help in the horsepower department...........but not like some of the companys who build them say they will. I mean your not gonna get 20 hp from a air filter, unless you already have the best of everything (i.e. larger cylinder heads, better exhaust,mass air meter, throttle body, injectors, camshaft, headers etc etc...) then you might would have a restriction with a K&N or its "equal" in the filter department......... the truth is you may get 5-6 hp on a given combo on a dyno with the right factors involved. But I very much doubt a stock 5.0 mustang wouldnt get some hp gain..........
do we least forget 1 or 2 horsepower here and there x's 10 makes 10-20 hp?