I have no idea about the performance part, but I know a easy way to take it out. If you don't already know this, here you go. If you do maybe I will benefit some one else.
'First, cap the end that goes into the engine. Your gonna have to get creative here and make a perfect seal. Stick a compressor hose in the other end and get it so its in there good. Now turn on your compressor and keep it at about 75psi if you can. Now light up your torch. Heat up the dent until it forces it out. Wear protective clothing because hot molten steel doesn't make a good shower if some thing goes wrong. It should 'iron out' the dent. The pipe may even preform better due to increased expansion.
I got this out of a issue of DIRT BIKE and I'm not going to take credit for it. If its common knowledge on this board, sorry, lol.