true, but k&n filters come equiped with oil charger, which functions 2 trap all residues n dirts... it's filter elements filter way better than stock filters do, at the same time let max air thru...
its true what praetorian said, without proper shielding heat can rob away power... i recommend that if u wanna proceed with the step, do it properly! for every 10*C rise in intake temp., 1 horsepower is loss!