Not on an LS,
But it depends on the pipes...2 1/8 try-ys with a crap collector will lose more bottom end than a set of 1 3/4" 4into1s with a good collector.
That said, I've had a bit to do with, Hi Torque, he did the tuning on a heap of mates LS commodores years ago, he knows his way around an LS so I would listen to what he has to say.