Im looking to add some exhaust to my 04 FX4 F-150. Im thinking about adding a FLOWMASTER 40 series single in and single out. Pretty much just replacing my muffler with the flow master and keeping all the stock pipes. Has anyone heard of or tried this? How does it sound?

 

Several do muffler swaps keeping the stock piping, so yes we've heard of it a lot. A Flowmaster will sound like a typical chambered muffler, not my liking but that's up to you. Search Youtube for soundclips of what you like.

 

I had similar setup but bumped piping to three inch. I would recommend a straight through muffler. Here are a couple videos of the two setups I have had. With stock piping it will just be a little less deep. Flowmaster forty and dynomax bullet.
https://www.f150forum.com/f4/flowmas...videos-126558/

 

i have it with a magnaflow 6"x18" round muffler and it sounds good to me not so much with volume but the tone is better if that makes sense

 

I would go cat back, you can just do a muffler swap. It will sound a lot better but for best results Dual that puppy out.