does the inlet/outlet size on a muffler matter?

I found me a nice Flowmaster 40 series muffler but it's not a 2.25" inlet/outlet, will the sound be louder or will it stay the same since my stock piping is 2.25"?

 

Should stay the same, depending on the actual size.
What are the inlet/outlet sizes?

 

they are both 3.0"

 

It'll be fine.
Difference will be negligible.

 

cool thanks.

 

i have a flowmaster 44. the inlet is 2.5" and the guy at the muffler shop cut the outlet and made it a dumper 3 inch outlet.. its pretty loud. My parents and some neighbors have complained. It gets the attention of authorities also. But it sounds nice

 

this one is the 40 series, don't think it will be that loud.
I had a 3" on my Blazer (I think it was a 44, I for a fact it was a Flowmaster though, it said on the muffler), got a fix it ticket but it was only due to everything being 3" already as well as me shortening the outlet pipe. lol when I was getting ti smogged, the smog person got mad that it was short, so he had me climb under and put that weird thing in the pipe. Even though it's 3" inlet/outlet on the muffler, I want to keep the piping stock (which is 2.25" for both inlet piping and outlet piping).
I may add in a tip but I have to see how it sounds overall before doing so.