Flowmasters will give you more of an old school muscle deep rumble and hollow sound off idle and through the midrange...Magnapacks will have a lil less rumble off idle, more of a burbly chugg sound and really wake up (very racey sound - Nascarish) between midrange and WOT. I frequently scare pedestrians and cause whiplash when I'm really stomping the guts outta the go pedal. 
