Do muffler muffler delete axle back exhausts harm the engine?

[370zsport]

Hey guys. I just got ordered a set of AAM short tails for my 2011 Z. They should be to me within a few days. I keep hearing about people losing a ton of low end torque, and am now a little concerned that the lack of back pressure may somehow damage the engine itself. I know I sound a little paranoid, but if anyone could shed some light on this, Id be very grateful. I just got my car back from the dealer after having the transmission, throw out bearing, clutch fluid, and rear axles replaced under warranty due to a faulty input shaft, and clicking in the rear from my axles. I just washed it and waxed it and want to put my first mod on it, and after hearing the AAM short tails, its the exact sound I am going for, I am just afraid of causing damage due to lack of back pressure.