Hehe...Time to come out of lurking for a second...
I got a Flowmaster 40 series muffler on my car a little over a month ago...Shop also replaced the piping after the muffler to 2¼" since the stock piping was rusted out...
I got a Flowmaster for my 2.3L because I liked the sound my dad got from his '03 Focus ZX3 when he installed a Flowmaster on it...For a 4-cylinder tone, it was really aggressive...It was throaty in it's own tone, and burbled a deep note as the revs climbed up...Of course, with my Mustang, I didn't expect to get anywhere near a V8 tone, but half the tone was still 50-times better than the annoying noise of a fartcan muffler to my ears...My 2.3 puts out a somewhat different sound than the Zetec, since the Zetec engine had variable valve/cam timing, so the tone varied throughout the revs, but it still had that distinctive tone for a 4-cylinder with the nice Flowmaster rumble...I could get erections standing behind my car when I let it run on idle, but that'd be wrong...Or would it?
Outside of sound, I also got it because of performance and fuel economy...It really picks up once you get going, and I'm sure I got a little more out of my milage too with the Flowmaster (Especially since these 2.3s aren't very efficient, since they're such a large engine for a 4-cylinder

)...