would you notice a power difference if a muffler was messed up

 

What exactly is "Messed UP"?? Is it smashed, collapsed internally, there is not a whole lot going on inside to fail.

 

i would say if it collapsed inside

 

Definitely gonna cause massive problems in the flow through of the muffler choking your engine out. Probably making it miss and run like ****. I have seen flowmaster break off internally before and do this but never a stock unit with packing but anything is possible.