I have an '85 camaro and I am looking to get a new muffler for it. It has the factory single exhaust all the way to the muffler. The muffler is single in, dual out. My dad says that the new muffler needs to be single in, dual out to make sure that it runs right. I don't think this is right because it shouldn't matter how the exhaust exits. It should perform the same with a single out as with a dual out. Who is right? Any help much appreciated.

shouldn't matter if they flow the same, fwiw, most single out will flow more than a comparable single out