The deal with exhaust is where do you want your torque? If you clog poop it up and it is quiet, she has a lot of grunt on the bottom. If you open the pipe, she flows faster and you want that more revving up top where you aim for the peak torque = 1/4 Mile exhaust kind of open pipe.
More questions dealing with your exhaust decisions are the cats and the 02 if so installed. You do not want to remove an 02 sensor, being the emissions tuning, and the cat is a must, being; you do not want that removed; especially for the street. And you sure do not want to remove the air pump to the exhaust (fresh air) dump either... These are needed tuning parts if you agree with a little physics theory...
See, you want the hot air to keep moving out of the pipe. Your back pressure is going to be hurt if you remove the cat for example. The cat keeps the pipe 'hot,' so the air pump can throw in fresh air and keep burning the unspent fuel. This reignites the fuel in the pipe so the unspent gas continues to push the 14.7 from reentering.
Again, if theory works in the practical is it works like in the absolute; your high/low pressure is a constant war for HP. Too much flow can send the fresh unspent out the exhausts hot air speed, where that pipe is all about cut and try to gain what torque range you are aiming for. Kind of think like this... Say the car is turned off. Inside the pipe is 14.7psi. If you agree, then that is the high pressure. Low pressure is the hot air moving in a, 'suck the air in the "overlap" causing a vacuum or a sucking action; being is it can push the 14.7 out of the pipe that the 'back pressure" of the 14.7 is trying to refill the exhaust pipe.
So, with that constant pressure/back into the pipe, it is a heat/speed/14.7 war of the HP/Torque move. It is that stink king pipe you gotta figure out is which one hits the spot?