I hope this is a joke. I don't know who to slap first you or the "older guy" at the shop.
1. It's common knowledge that a muffler will give you no horsepower gains. It'll change the pitch of the exhaust note. That's it.
2. Changing the size of the exhaust tubing is what gives you more horsepower. You're allowing more flow so the engine can exhale quicker. Anyone working at a exhaust shop knows this.
This all sounds fishy, if you knew anything about cars then you would have known that the whole point of changing the exhaust is to get larger exhaust tubing. You just spent $110 and you didn't touch your performance at all. Like I said this sounds fishy so I'm gonna bring up the flag
. I'm sorry if I've got something wrong but this doesn't seem right. I can't see why the guys at the exhaust shop would be so baffled as to why you want a larger exhaust. Maybe I just misunderstood so let me know.