Your going to need more flow mods. That thing is going to have more knock than before because the GenV is more efficient than the GenIII...an SLP catback isn't a flow mod either...the weak spot is the manifolds/DP/U-bend...I'd get the GenV and put headers on it at the same time...like the Speed Daddys...they are less than $250 and then you never have to worry about flow mods.