Do these mods actually add hp?

[dabouncerx24]

pdiggs your suggestions are really good, but one thing I really can't stand is the oval design, it's hideous. I'm sure those Magnaflow and Superturbo mufflers are good mufflers since you think highly of them, but I really can't imagine my car having something shaped like that attached to it. Big part of the reason I like the Apex'i N1 is because of how the muffler is shaped...is there other cheaper quality brands that produce the same type of muffler canister that you know of?
Do I necessarily have to get a highflo cat to get my exhaust system to reach its full potential?
What exactly does a resonator do? And why the longer the better? kteller only offers 18in the longest